The Master and His Emissary: The Divided Brain and the Making of the Western World - Iain McGilchrist (2009)
Part I. THE DIVIDED BRAIN
Chapter 2. WHAT DO THE TWO HEMISPHERES ‘DO’?
HOW MUCH NEUROLOGICAL AND NEUROPSYCHOLOGICAL EVIDENCE IS THERE that the hemispheres really are all that different? Or, if there are differences, that there are consistent and significant patterns to the differences, rather than just a random carve-up of ‘functions’ according to the dictates of space? (This ‘toy cupboard’ model, which is represented by the traditional view that brain functions are just accommodated according to where space can be found or made, is the one invoked to explain the residence of language functions in the left hemisphere.) Surely, it may be said, the really important differences are those between the many further subdivided functional and anatomical areas descrbed by neuroscience within each hemisphere?
Such differences are certainly of huge significance. However to de-scribe (write about) any thing is to select amongst an infinity of possible features: it is inevitably to circum-scribe (draw a line round) what is salient for the purpose. In comparing two cars, for example, it is obviously true – but, for the time being, irrelevant – that there are far greater similarities between the two cars as a whole than there are differences between, say, their engines. But the point of comparing them is to focus on their differences. My interest here, then, is not in the myriad similarities, which go without saying, but precisely in the differences between the hemispheres. There is, however, one very important intrahemispheric rather than interhemispheric regional difference that I will need to refer to, because it cannot, in the nature of things, be disentangled from the larger question; I will deal with this at the end of the chapter, where I hope it will make most sense.
I would also caution against the natural tendency of the analytic approach, having unimpeachably distinguished parts, to see the parts, rather than the systemic whole to which they belong, as of primary significance. Science involves both analysis and synthesis of knowledge. Increasingly we realise that no one ‘bit’ of the brain can be responsible for anything that we experience: the brain is a dynamic system, and it is to systemic wholes, ‘composed’ of many post factum identifiable parts, that we need to attend. When we divide, we would be best to divide where nature has clearly made a division: between the hemispheres. In what follows, where I refer, as I often do, to regions within the hemisphere, it should be taken for granted that the important activity is not confined to that region alone, but that it acts in concert with many others, principally, though not of course confined to, regions within the same hemisphere.1
There are, as it happens, pervasive and consistent differences between the hemispheres, existing at many levels.
Starting once again with the structure, most studies have found that the right hemisphere is longer, wider, and generally larger, as well as heavier, than the left.2 Interestingly this is true of social mammals in general.3 The right hemisphere is in fact wider than the left throughout most of its length, only the posterior parieto-occipital region being broader in the left hemisphere.4 The cerebral hemispheres show a highly consistent right-greater-than-left asymmetry from childhood to adulthood, with the ventricles (spaces within the hemisphere that are filled with cerebrospinal fluid, and form effectively an inverse measure of brain volume) being larger on the left.5 However, the expansion of the speech areas in the left hemisphere is also very early in origin and is detectable from 31 weeks' gestation, being clearly present during most of the last trimester.6
As well as differing in the size and shape of a number of defined brain areas,7 the hemispheres differ in the number of neurones,8 neuronal size (the size of individual nerve cells),9 and the extent of dendritic branching (the number of connective processes put out by each nerve cell) within areas asymmetrically.10 There is greater dendritic overlap in cortical columns in the right hemisphere, which has been posited as a mechanism for greater interconnectivity compared with the left.11 The ratio of grey to white matter also differs.12 The finding that there is more white matter in the right hemisphere, facilitating transfer acrossregions, also reflects its attention to the global picture, where the left hemisphere prioritises local communication, transfer of information within regions.
Neurochemically the hemispheres differ in their sensitivity to hormones (for example, the right hemisphere is more sensitive to testosterone),13 and to pharmacological agents;14 and they depend on preponderantly different neurotransmitters (the left hemisphere is more reliant on dopamine and the right hemisphere on noradrenaline).15 Such structural and functional differences16 at the brain level suggest there may indeed be basic differences in what the two hemispheres do. So what does the neuropsychological literature tell us about that?
While it is true that we know a lot about what different, in some cases fairly minutely discriminated, areas within each hemisphere ‘do’, in the sense that we can answer the question ‘what’ it is that they appear to help mediate, we have tended to pay less attention to the ‘how’, the way in which they do this – not in the sense of the mechanism by which they do it, of which we have a rapidly increasing understanding, but in the sense of what aspect of a certain ‘function’ is being addressed. As soon as one starts to look in this way at the question – for example, not where language is, but what aspects of language are where – striking differences between the hemispheres emerge.17
THE PATHWAYS TO KNOWLEDGE
Brain structure is easy to measure, function more problematic. So let me start by saying something of the ways in which we come to have knowledge of brain functioning, and some of the problems associated with them. This is important because there is a tendency, particularly among non-specialists, to believe that, thanks to modern technology, we can easily ‘see’ which parts of the brain are involved in almost any human activity.
The first thing to make clear is that, although the brain is often described as if it were composed of bits – ‘modules’ – of one kind or another, which have then to be strung together, it is in fact a single, integrated, highly dynamic system. Events anywhere in the brain are connected to, and potentially have consequences for, other regions, which may respond to, propagate, enhance or develop that initial event, or alternatively redress it in some way, inhibit it, or strive to re-establish equilibrium. There are no bits, only networks, an almost infinite array of pathways. Thus, especially when dealing with complex cognitive and emotional events, all references to localisation, especially within a hemisphere, but ultimately even across hemispheres, need to be understood in that context.
Having said that, how can one make a start? One method is to study subjects with brain lesions. This has certain advantages. When a bit of the brain is wiped out by a stroke, tumour or other injury, we can see what goes missing, although interpretation of the results is not always as straightforward as it might seem.18 Another is to use temporary experimental hemisphere inactivations. One way in which this is achieved is by the Wada procedure, most commonly carried out prior to neurosurgery in order to discriminate which hemisphere is primarily responsible for speech. This involves injecting sodium amytal or a similar anaesthetic drug into the blood supply of one carotid artery at a time, thus anaesthetising one half of the brain at a time, while the other remains active. Another way is through transcranial magnetic stimulation techniques, which uses an electromagnet to depress (or, depending on the frequency, enhance) activity temporarily in one hemisphere, or at a specific location within the hemisphere. In the past a similar opportunity came from unilateral administration of electroconvulsive therapy (ECT); it was then possible to ask the subject to carry out specific tasks, in the knowledge that one hemisphere was inactivated for about 15–20 minutes following treatment.
Further techniques that can be helpful involve delivering a perceptual stimulus to one hemisphere only. The tachistoscope is a way of delivering a visual stimulus for a few milliseconds only, too short for gaze to be redirected; careful placement of the stimulus enables it to be delivered to one half of the visual field only. Dichotic listening techniques deliver different stimuli to either ear, usually through headphones, and this was one of the ways in which it was first established that in general there is an advantage for the right ear (left hemisphere) in dealing with verbal material. But in the intact brain we can assume that information spreads very quickly to the contralateral hemisphere, so in using these techniques one is looking at small differences in reaction times, or marginal differences in salience.
For this reason a particularly rich resource has been individuals with so-called split brains, patients who, in order to control intractable epilepsy, underwent a procedure called callosotomy, which divides the corpus callosum. This operation is rare nowadays, as most seizures are controllable with modern pharmacological agents, but when it was first carried out, by Sperry and Bogen and their colleagues in California in the 1950s and 1960s, it was revolutionary – both for the patients, who began to lead normal lives, and for neurologists, psychologists and philosophers, who saw a window opened into the workings of the brain. In the case of split-brain subjects, stimuli presented to one ear or to one visual field cannot be transferred across the corpus callosum to the other hemisphere, giving a relatively pure picture of how one hemisphere on its own responds, which is why they are so valuable to researchers. Some particular circumstances make split-brain subjects especially intriguing. If an image is shown to a split-brain subject in the left visual field, he or she will be unable to name what was seen, since the image from the left visual field is sent to the right side of the brain only, and the right hemisphere in most subjects cannot speak. Since interhemispheric communication is largely absent, the speaking left hemisphere cannot name what the right hemisphere has just seen. The person can nonetheless indicate a corresponding object with his or her left hand, since that hand is controlled by the right side of the brain.
Other information comes from EEG recordings, and increasingly from functional neuroimaging, which allows one to see which areas of the brain are preferentially activated while performing a task, and this area is promising. The information from the EEG is instantaneous, and therefore quite precise in time, but harder to localise precisely in the brain. By contrast, functional magnetic resonance imaging (fMRI), the preferred method of imaging now available, gives more precise localisation, but with a three- to five-second time spread. These techniques can be combined. Neuroimaging, including single photon emission computed tomography (SPECT) and positron emission tomography (PET), as well as fMRI, use a variety of techniques to detect where there are changes in the perfusion (blood supply) of the brain, the common principle being that active areas metabolise at a higher rate and therefore require a temporarily increased blood supply. It is worth saying something, however, about the problems associated with neuroimaging studies as a source of information on their own.19
Imaging just shows a few peaks, where much of interest goes on elsewhere.20 One cannot assume that the areas that light up are those fundamentally responsible for the ‘function’ being imaged, or that areas that do not light up are not involved.21 And, what is more, one cannot even assume that whatever ‘peaks’ is of primary importance, since only effortful tasks tend to register – the more expert we are at something the less we will see brain activity. For example, people with higher IQs have lower cerebral metabolic rates during mentally active conditions;22 as do those with bigger brain size,23 which is also correlated with IQ.24 We have, too, to remember that the activations we visualise in the brain may actually be inhibitory in nature – inhibition may be indistinguishable from activation using current fMRI methods.25
That does not nearly exhaust the problems to be surmounted. Small differences in the way the task is presented may make a large difference to the results. Changes in novelty or complexity can mask relevant structures or falsely identify irrelevant ones.26 The more complex the task, the more widely distributed the networks involved are likely to be, and the harder it will be to know what it is that one is measuring; subtraction paradigms, where two sets of conditions are compared so as to isolate the element of interest, are associated with their own problems.27
As if that is not enough, many variables are involved in any experiment involving human beings. Male and female subjects respond differently; not only left and right handedness may make a difference, but more importantly, strongly lateralised handedness (whether right or left) may give a different picture from more mixed handedness; race and age also make differences. Individual cases may be different because the way we experience the world individually is different; even the same brain varies in its response to the same task depending on the context – for example, what's happened previously. In the words of one prominent neuroimaging specialist: ‘Some people believe that psychology is just being replaced by brain imaging, but I don't think that's the case at all … It's the confrontation of all these different methods that creates knowledge.’28
For all these reasons I have tried throughout not to rely on neuroimaging only, and as little as possible on any one line of evidence alone. The importance of, wherever possible, linking neuroimaging with evidence from brain lesion studies has recently been emphasised in relation to the concept of ‘theory of mind’.29 But, as I began by pointing out, even brain lesion studies have their limitations.30
All in all, it should be clear that anything like complete concurrence of findings is not to be expected; there are bound to be many discrepancies, and overall this is not as precise a science as it may appear. Nonetheless in aggregate we have a mass of information that does suggest consistent differences, and it's at these we need to take a closer look.
In doing so, I will sometimes refer to brain regions illustrated in Figures 2.1 and 2.2, specifically parts of the prefrontal cortex, the diencephalon, basal ganglia, and the limbic system, and, while the argument can be followed without a knowledge of detailed anatomy, the images may help readers not familiar with the area.
I should also say that this is necessarily a very long chapter. I recognise that that may be a little disheartening to the reader, and I could have divided it into several parts. But my hope is that we can get away from looking at separate ‘areas of cognition’, however much I may have had to carve up the seamless world each hemisphere delivers into recognisable chunks for the purposes of description. In the process of doing so, I have been keenly aware of the artificiality of such divisions, since each inevitably overlaps with many others, and ultimately I believe they form a single, coherent whole. To have cut it up further into separate chapters would have reinforced the tendency I wish to avoid. But the various subheadings of this chapter are a compromise which will, I hope, give the process some sense of direction.
Fig. 2.1 Prefrontal cortex and limbic system
Fig. 2.2 Diencephalon, basal ganglia and limbic system
BREADTH AND FLEXIBILITY VERSUS FOCUS AND GRASP
I'd like to begin with what we have already touched on, the fundamental importance of attention. If what it is that exists comes into being for each one of us through its interaction with our brains and minds, the idea that we could have a knowledge of it that was not also an expression of ourselves, and dependent on what we brought to the relationship, is untenable. It may seem obvious, though, that the task of the brain – what we have a brain for – is to put us in touch with whatever it is that exists apart from ourselves.
But this conclusion is not quite as obviously right as it seems. Different aspects of the world come into being through the interaction of our brains with whatever it is that exists apart from ourselves, and precisely which aspects come into being depends on the nature of our attention. It might turn out that for some purposes, those that involve making use of the world and manipulating it for our benefit, we need, in fact, to be quite selective about what we see. In other words we might need to know what is of use to us – but this might be very different from understanding in a broader sense, and certainly might require filtering out some aspects of experience. Without experiencing whatever it is, we would have nothing on which to ground our knowledge, so we have to experience it at some stage; but in order to know it, we have to ‘process’ experience. We have to be able to recognise (‘re-cognise’) what we experience: to say this is a ‘such-and-such’, that is, it has certain qualities that enable me to place it in a category of things that I have experienced before and about which I have certain beliefs and feelings. This processing eventually becomes so automatic that we do not so much experience the world as experience our representation of the world. The world is no longer ‘present’ to us, but ‘re-presented’, a virtual world, a copy that exists in conceptual form in the mind.
Much of our capacity to ‘use’ the world depends, not on an attempt to open ourselves as much as possible to apprehending whatever it is that exists apart from ourselves, but instead on apprehending whatever I have brought into being for myself, my representation of it. This is the remit of the left hemisphere, and would appear to require a selective, highly focussed attention.
The right hemisphere, as birds and animals show, is ‘on the look out’. It has to be open to whatever it is that exists apart from ourselves, as much as possible without preconceptions, not just focussing on what it already knows, or is interested in. This requires a mode of attention that is broader and more flexible than that of the left hemisphere. What actually happens in detail?
The conventional neuropsychological literature distinguishes five types of attention: vigilance, sustained attention, alertness, focussed attention and divided attention. While not identical, vigilance and sustained attention are similar, and they are often treated as one concept. Together with alertness, they form the basis of what has been called the intensity axis of attention. The other axis is selectivity, made up of the two remaining types, focussed and divided attention.31 Experiments confirm that the different types of attention are distinct and independent of one another, and subserved by a number of different brain structures distributed extensively over the prefrontal, anterior cingulate, and posterior parietal areas of both hemispheric cortices. Clearly within either hemisphere, and possibly between hemispheres, the system of control processes is complex. However, some broad consistent differences in hemisphere specialisation are striking when one comes to review the available evidence.
Alertness and sustained attention may have the ring of technical ‘functions’, just the sort of things it's hard to get excited about outside the psychology lab. But, like vigilance, they are the ground of our being in the world, not only at the lowest, vegetative level, but at the highest, spiritual levels (‘Brethren, be sober, be vigilant', ‘O Mensch, gib acht!’).32 Without alertness, we are as if asleep, unresponsive to the world around us; without sustained attention, the world fragments; without vigilance, we cannot become aware of anything we do not already know. Looking at the evidence from brain research, it becomes clear that vigilance and sustained attention are grossly impaired in subjects with right-hemisphere lesions, especially right frontal lobe lesions;33 by contrast, in patients with left-hemisphere lesions (therefore relying on their intact right hemisphere) vigilance is preserved.34 Patients with right-hemisphere lesions also exhibit what is called perceptuomotor slowing, a sign of diminished alertness, associated with lapses of attention.35 Studies in both healthy subjects and split-brain patients corroborate the role of the right hemisphere in the ‘intensity’ aspects of attention;36 and scanning studies provide further confirmatory evidence of right-hemisphere dominance in alertness and sustained attention.37 Overall it appears clear that, of the two main axes of attention, intensity (alertness, vigilance and sustained attention) is reliant on the right hemisphere.
The other main axis of attention is selectivity (focussed and divided attention). Turning to focussed attention first, the story here is quite different. Deficits in focussed attention are more severe with left-hemisphere injury.38 Although selective attention may be bilateral,39 it is more typically associated with activity in the left caudate or left anterior cingulate.40 Healthy subjects show a left-hemisphere preference for choice reactions.41 And scanning studies suggest focussed attention is associated with activity in the left orbitofrontal cortex and basal ganglia.42
As regards divided attention, the evidence is divided. While some studies suggest that both left and right hemispheres are involved,43 there appears to be a clear primary role for the right hemisphere, especially the right dorsolateral prefrontal cortex.44
To sum up, the right hemisphere is responsible for every type of attention except focussed attention. Even where there is divided attention, and both hemispheres appear to be involved, it seems probable that the right hemisphere plays the primary role (possibly that of unifying the divided input – see below). Because it is the right hemisphere that is responsible for attention globally, and because there is a natural tendency for each hemisphere to process preferentially stimuli from the contralateral attentional field, most people, if asked to bisect a line, will do so slightly to the left of the actual midpoint – because doing so equalises the apparent extent of the half-lines as seen from the right hemisphere's point of view.45 It is lesions in the right inferior parietal lobule that cause the most serious impairment of global attention.46
There have been suggestions that the basis for the right-hemisphere predominance for attention may lie in the more sophisticated visuospatial processing of the right hemisphere, but I would be inclined to see that as a consequence of the attentional difference rather than a cause of it.47
More specifically there is evidence of left-hemisphere dominance for local, narrowly focussed attention and right-hemisphere dominance for broad, global, and flexible attention.48 The scope of the right hemisphere's world is broad.49 Patients with a right-hemisphere lesion (therefore relying on their intact left hemisphere) start with the pieces and put them together to get the overall picture, whereas those with a left-hemisphere lesion (relying on their right hemisphere) prefer a global approach.50 Patients with right-hemisphere damage don't seem able to adjust the breadth of the ‘spotlight’ of their attention: they suffer ‘an excessive and more or less permanent narrowing of their attentional window’.51 That's what happens when we have to rely on left-hemisphere attention on its own.
THE NEW VERSUS THE KNOWN
From this it follows that in almost every case what is new must first be present in the right hemisphere, before it can come into focus for the left. For one thing, the right hemisphere alone attends to the peripheral field of vision from which new experience tends to come; only the right hemisphere can direct attention to what comes to us from the edges of our awareness, regardless of side.52 Anything newly entering our experiential world instantly triggers a release of noradrenaline – mainly in the right hemisphere.53 Novel experience induces changes in the right hippocampus, but not the left.54 So it is no surprise that phenomenologically it is the right hemisphere that is attuned to the apprehension of anything new.55
This difference is pervasive across domains. Not just new experience, but the learning of new information or new skills also engages right-hemisphere attention more than left,56 even if the information is verbal in nature.57 However, once the skills have become familiar through practice, they shift to being the concern of the left hemisphere,58 even for skills such as playing a musical instrument.59
If it is the right hemisphere that is vigilant for whatever it is that exists ‘out there’, it alone can bring us something other than what we already know. The left hemisphere deals with what it knows, and therefore prioritises the expected – its process is predictive. It positively prefers what it knows.60 This makes it more efficient in routine situations where things are predictable, but less efficient than the right wherever the initial assumptions have to be revised,61 or when there is a need to distinguish old information from new material that may be consistent with it.62 Because the left hemisphere is drawn by its expectations, the right hemisphere outperforms the left whenever prediction is difficult.63 The link between the right hemisphere and what is new or emotionally engaging exists not just in humans, but already in higher mammals: for example, horses perceive new and possibly emotionally arousing stimuli with the left eye.64
POSSIBILITY VERSUS PREDICTABILITY
The right hemisphere is, in other words, more capable of a frame shift;65 and not surprisingly the right frontal lobe is especially important for flexibility of thought, with damage in that area leading to perseveration, a pathological inability to respond flexibly to changing situations.66 For example, having found an approach that works for one problem, subjects seem to get stuck, and will inappropriately apply it to a second problem that requires a different approach – or even, having answered one question right, will give the same answer to the next and the next. It is the right frontal cortex that is responsible for inhibiting one's immediate response, and hence for flexibility and set-shifting;67 as well as the power of inhibiting immediate response to environmental stimuli.68
It is similar with problem solving. Here the right hemisphere presents an array of possible solutions, which remain live while alternatives are explored.69 The left hemisphere, by contrast, takes the single solution that seems best to fit what it already knows and latches onto it.70 V. S. Ramachandran's studies of anosognosia reveal a tendency for the left hemisphere to deny discrepancies that do not fit its already generated schema of things. The right hemisphere, by contrast, is actively watching for discrepancies, more like a devil's advocate.71 These approaches are both needed, but pull in opposite directions.
This difference is not predicated on any of the old distinctions such as verbal versus visuospatial. It operates equally in the realm of attention to verbal information. In keeping with what we know of its priorities, the left hemisphere actively narrows its attentional focus to highly related words while the right hemisphere activates a broader range of words. The left hemisphere operates focally, suppressing meanings that are not currently relevant. By contrast, the right hemisphere ‘processes information in a non-focal manner with widespread activation of related meanings’.72 Whereas close lexical semantic relationships rely more on the left hemisphere, looser semantic associations rely on the right.73 Because the right hemisphere makes infrequent or distantly related word meanings available,74 there is increased right-hemisphere involvement when generating unusual or distantly related words75 or novel uses for objects.76 This may be one of many aspects that tend to associate the right hemisphere with a freer, more ‘creative’ style. The right anterior temporal region is associated with making connections across distantly related information during comprehension,77 and the right posterior superior temporal sulcus may be selectively involved in verbal creativity.78 In the ‘close’ situation, by contrast, the left hemisphere actively suppresses the right, to exclude associations which are semantically only distantly related.79
The more flexible style of the right hemisphere is evidenced not just in its own preferences, but also at the ‘meta’ level, in the fact that it can also use the left hemisphere's preferred style, whereas the left hemisphere cannot use the right hemisphere's. For example, although the left hemisphere gains more benefit from a single strong association than several weaker associations, only the right hemisphere can use either equally.80
One of the standard psychological tests that is supposed to measure creativity is the Remote Association Test, an expression of the belief that creativity requires the ability to make associations between widely different ideas or concepts.81 Since efforts of will focus attention and deliberately narrow its range,82 it may be that cessation of the effort to ‘produce something’ – relaxation, in other words – favours creativity because it permits broadening of attention, and, with the expansion of the attentional field, engagement of the right hemisphere.83 (From what has been said it can be seen that relatively more remote or tenuous associations of thought are made more easily by permitting the broader scope of right-hemisphere attention, which may also explain the ‘tip of the tongue’ phenomenon: the harder we try, the more we recruit narrow left-hemisphere attention, and the less we can remember the word. Once we stop trying, the word comes to us unbidden.)
Since the left hemisphere actually inhibits the breadth of attention that the right hemisphere brings to bear, creativity can increase after a left-hemisphere stroke, and not just in sensory qualities but, as Alajouanine says of one painter he describes, in ‘numerous intellectual and affective components’.84 Certainly there is plenty of evidence that the right hemisphere is important for creativity,85 which given its ability to make more and wider-ranging connections between things, and to think more flexibly, is hardly surprising.86 But this is only part of the story. Both hemispheres are importantly involved. Creativity depends on the union of things that are also maintained separately – the precise function of the corpus callosum, both to separate and connect; and interestingly division of the corpus callosum does impair creativity.87
INTEGRATION VERSUS DIVISION
In general the left hemisphere is more closely interconnected within itself, and within regions of itself, than the right hemisphere (see p. 33 above).88 This is all part of the close focus style, but it is also a reflection at the neural level of the essentially self-referring nature of the world of the left hemisphere: it deals with what it already knows, the world it has made for itself. By contrast, as I have mentioned, the right hemisphere has a greater degree of myelination, facilitating swift transfer of information between the cortex and centres below the cortex,89 and greater connectivity in general.90 Functionally its superior integration is evidenced by EEG measures91 and by the more diffuse but overlapping somatosensory projections (carrying information on touch, pain and body position) and auditory inputs on the right side of the brain.92
At the experiential level it is also better able to integrate perceptual processes, particularly bringing together different kinds of information from different senses.93 There is evidence from brain-damaged war veterans that confirms the difference between the left hemisphere's focal organisation and the right hemisphere's more profuse and diffusely organised structure, and indicates that this may be why the right hemisphere has the advantage in constructing a richly diverse three-dimensional world in space. We would expect on first principles that having widely different kinds of functions grouped together in the more diffusely organised right hemisphere should lead to a different quality of integration from that characteristic of the more focally organised left hemisphere: there would be a greater convergence of disparate types of information, and ‘one might predict heteromodal integration to an extent surpassing that possible in a focally organised hemisphere.’94 In plain English, this means bringing together in consciousness different elements, including information from the ears, eyes, and other sensory organs, and from memory, so as to generate the richly complex, but coherent, world we experience. By contrast, the left hemisphere wouldbe ‘inadequate for the more rapid complex syntheses achieved by the [right] hemisphere’.95
I mentioned that new stimuli lead to release of noradrenaline in the right hemisphere. Most neurones ‘fatigue’, that is to say they cease to respond, when continuously stimulated. These noradrenergic neurones do not fatigue, however, but maintain their condition of excitation, so that exploratory attention is held open across a greater expanse of both space and time.96 The range of the right hemisphere is further increased by the fact that it has a longer working memory, and so is able both to access more information and hold it together at any one time for longer.97 It is capable of bearing more information in mind and doing so over longer periods, with greater specificity (which also means less susceptibility to degradation over time by memory).98
This broader field of attention, open to whatever may be, and coupled with greater integration over time and space, is what makes possible the recognition of broad or complex patterns, the perception of the ‘thing as a whole’, seeing the wood for the trees.99 In short the left hemisphere takes a local short-term view, whereas the right hemisphere sees the bigger picture.
THE HIERARCHY OF ATTENTION
There are, then, two widely differing ways of attending to the world. How do they relate to one another?
If whatever is new to experience is more likely to be present in the right hemisphere, this suggests a temporal hierarchy of attention, with our awareness of any object of experience beginning in the right hemisphere, which grounds experience, before it gets to be further processed in the left hemisphere.
This coexists with and is confirmed by a hierarchy of attention at any one moment in time, which also establishes the right hemisphere, not the left, as predominant for attention.100 Global attention, courtesy of the right hemisphere, comes first, not just in time, but takes precedence in our sense of what it is we are attending to; it therefore guides the left hemisphere's local attention, rather than the other way about.101 As an illustration, we would normally see the images below as an H (composed of Es) and a 4 (composed of 8s).
The exception to this is in schizophrenia, where the right-hemisphere-dependent ability to see the whole at once is lost; then the figure becomes just a mass of Es and 8s. One of the crucial differences in schizophrenia – and in schizotypy – lies in the mode of attention, whereby the whole is built up from the parts.102 However, the attentional hierarchy can also be inverted in certain circumstances in normal individuals.103 When there is a high probability that what we are looking for lies at the local level, our window of attention narrows, in order to optimise performance at this level, ‘thus reversing the natural tendency to favour the global aspect’.104
Essentially the left hemisphere's narrow focussed attentional beam, which it believes it ‘turns’ towards whatever it may be, has in reality already been seized by it.105 It is thus the right hemisphere that has dominance for exploratory attentional movements, while the left hemisphere assists focussed grasping of what has already been prioritised.106 It is the right hemisphere that controls where that attention is to be oriented.107
We may think that we build up a picture of something by a process of serial scanning – putting the bits together – because this is the way our conscious, verbal, left hemisphere, when asked to work out how it is done after the fact, accounts for it. But in reality we see things first whole: serial attentional processing is not needed. In other words, we do not have to orientate our attention to each feature of an object in turn to understand the overall object; the features are all present without the need to combine the products of focal attention.108
Beyond the difference in nature and extent of the attention that the two hemispheres give to the world, there is a fascinating and fundamental difference in their orientation. One might think that both hemispheres would take the world as a whole as their concern, or, if it is impossible for both to do so, that there would be a symmetrical and complementary distribution of attention across the whole field. But this is not the case. Since the left visual field, and the perceptions of the left ear, are more available to the right hemisphere, and by the same token the right visual field, and the perceptions of the right ear to the left hemisphere, one would expect, and indeed one finds, a gradient of attention from left to right, or right to left, across the experiential world for either hemisphere. But these gradients are not symmetrical: there is a fundamental asymmetry of concern about the whole picture. The right hemisphere is concerned with the whole of the world as available to the senses, whether what it receives comes from the left or the right; it delivers to us a single complete world of experience. The left hemisphere seems to be concerned narrowly with the right half of space and the right half of the body – one part, the part it uses.109
In split-brain patients, for example, the right hemisphere attends to the entire visual field, but the left hemisphere only to the right.110 This refusal of the left hemisphere to acknowledge the left half of the world accounts for the fascinating phenomenon of ‘hemi-neglect’ following a right-hemisphere stroke, after which the individual is completely dependent on the left hemisphere to bring his body and his world into being.111 Because the concern of the left hemisphere is with the right half of the world only, the left half of the body, and everything lying in the left part of the visual field, fails to materialise (see Figure 2.3). So extreme can this phenomenon be that the sufferer may fail to acknowledge the existence of anyone standing to his left, the left half of the face of a clock, or the left page of a newspaper or book, and will even neglect to wash, shave or dress the left half of the body, sometimes going so far as to deny that it exists at all.
This is despite the fact that there is nothing at all wrong with the primary visual system: the problem is not due to blindness as ordinarily understood. If one temporarily disables the left hemisphere of such an individual through transcranial magnetic stimulation, the neglect improves, suggesting that the problem following right-hemisphere stroke is due to release of the unopposed action of the left hemisphere.112 But you do not get the mirror-image of the neglect phenomenon after a left-hemisphere stroke, because in that case the still-functioning right hemisphere supplies a whole body, and a whole world, to the sufferer. And, because the right hemisphere alone subserves the extremities of the attentional field (whether left or right), where hemi-neglect results in loss of the left field, there is, extraordinarily enough, also loss of the extreme right field.113
There is a curious phenomenon of ‘stickiness’ about the attention exhibited by the left hemisphere, which is related to its relative inflexibility referred to above. Following right-hemisphere damage, the right hemifield seems to exert a magnetic attraction.114 Patients find their gaze pulled, despite themselves, towards the right.115 And it has even been suggested that the phenomenon of attentional hemineglect is not so much a matter of disregarding the left side of space, as of being captured by the right side of space, and unable to let go.116 The left hemisphere has difficulty disengaging;117 and this seems to be precisely because, instead of familiarity causing it to disattend, it causes it to attend all the more. Patients start off by being attracted towards items on the right, but then become stuck to them, because instead of causing inhibition (negative feedback), as would normally be the case, repeated or familiar stimuli on the right side cause facilitation (positive feedback).118 A patient of mine who had had a right-hemisphere stroke following rupture of an arteriovenous malformation in his temporoparietal region would become fixated by inanimate objects in his right hemifield: if there was a door hinge to his right, for example, he would find himself waylaid by it as he tried to pass through the doorway, and get ‘stuck’ inspecting it for protracted periods, unless actively disengaged by one of his carers.
Fig. 2.3 Templates copied by patients with neglect (© 2008 by Nigel J. T. Thomas)
It is probably relevant that it is the right hemisphere that controls conjugate eye movements, that is, that makes the two eyes move together,119 leading to the interesting thought that it may be the right hemisphere that also keeps the hemispheres together, in the interests of a whole world of experience, rather than allowing the left hemisphere wilfully to go its own way.
In summary, the hierarchy of attention, for a number of reasons, implies a grounding role and an ultimately integrating role for the right hemisphere, with whatever the left hemisphere does at the detailed level needing to be founded on, and then returned to, the picture generated by the right. This is an instance of the right left right progression which will be a theme of this book. And it lies at the very foundation of experience: attention, where the world actually comes into being.
But that does not quite complete the picture. There is a further highly significant point to be observed here about the relationship between the hemispheres. It will be remembered that chicks use either eye for different purposes and different views of the world. Chicks using both eyes, however, do not do the splits: they approximate more to the right-hemisphere view.120 That is in keeping with what we would expect from everything we have heard about the attentional hierarchy. But it may also have to do with the fact that at this stage their hemispheres are relatively independent. For we know that, in the adult birds, the commissures which develop – the bands of nerve tissue, such as the corpus callosum, that connect the two hemispheres – permit the left hemisphere to have an inhibitory effect on the right hemisphere to a greater extent than the right hemisphere has on the left. In doing so they actually succeed in reversing the natural asymmetry: they impose the left-hemisphere view of the world. Only when interhemispheric communication is rendered impossible by severing of the commissures does one see, once again, the natural asymmetry in favour of the right hemisphere's view of the world appear.121
THE WHOLE VERSUS THE PART
I have mentioned that the link between the right hemisphere and holistic or Gestalt perception is one of the most reliable and durable of the generalisations about hemisphere differences, and that it follows from the differences in the nature of attention.122
Fig. 2.4 Emergence of the Gestalt
The right hemisphere sees the whole, before whatever it is gets broken up into parts in our attempt to ‘know’ it. Its holistic processing of visual form is not based on summation of parts. On the other hand, the left hemisphere sees part-objects.123 The best-known example of this process of Gestalt perception is the way in which the Dalmatian dog, sniffing the ground in the shade of a tree, suddenly emerges from this mass of dots and splashes (Figure 2.4). The process is not a gradual putting together of bits of information, but an ‘aha!’ phenomenon – it comes all at once.
The right hemisphere, with its greater integrative power, is constantly searching for patterns in things. In fact its understanding is based on complex pattern recognition.124
Split-brain subjects have a complete inability to relate the shape or structure of something they have seen to something they feel with their hand – if the object is felt with their right hand. With the left hand (right hemisphere), however, they perform perfectly.125 Gazzaniga and LeDoux thought this must be dependent on some sort of tactile or ‘manipulatory’ advantage of the ‘minor’ hemisphere, because they were able to show that in a second experiment involving visual–visual integration, involving fitting a broken figure together, the left hemisphere was not so bad (though it was still not as good as the right hemisphere). See Figure 2.5.
But this second test is hardly much of a test of the capacity to generate a sense of the whole. A test of the capacity to generate a sense of the whole would be, precisely, to have a sense of what it would be like in modalities other than those in front of one – to be able to tell from the feel of something what it would look like, never having seen it; or to be able to select by touch alone an object that had been seen – the capacity which the left hemisphere lacks.
Fig. 2.5 Split-brain subjects and sense of the whole (Gazzaniga & Le Doux, 1978)
Fig. 2.6 Right hemisphere damage and loss of the sense of the whole (Hécaen & Ajuriaguerra, 1952)
Subjects with unilateral brain damage show complementary deficits in drawing skills, depending on whether it is right or left hemisphere function that is compromised. The productions of those with right-hemisphere damage, relying on their left hemisphere, lose overall coherence and integrity, and become so distorted they are barely recognisable: there is no grasp of the Gestalt, the whole. For example, if asked to draw a person, subjects with right parieto-occipital lesions ‘exhibit considerable difficulty in assembling the various elements correctly, in their repeated attempts putting the limbs in extraordinary positions (arms attached to the neck or to the lower part of the trunk)’. One patient, asked to draw an elephant, ‘draws only a tail, a trunk and an ear.’ Putting together a model of an elephant is no easier: it ‘is done slowly and ends in a complete fiasco. Although, from what he says, he recognises the essential elements, he is incapable of putting them in even approximately the right place or relation to one another.’126 Figures become almost unbelievably simplified and distorted: a man, just a blob with three sticks for limbs; a bicycle, two small wheels positioned above the (bigger) pedals; a house reduced to a few chaotic lines, with a roof symbolised by an inverted V. See Figure 2.6.
The drawings of those with left-hemisphere damage, by contrast, relying on their right hemisphere, sometimes exhibit relative poverty of detail, because the accent is on the shape of the whole.127 See Figure 2.7.128
It is the same with perception, as with execution. For example, a patient with right-hemisphere damage described by Hécaen and de Ajuriaguerra was unable to recognise a drawing of a house, until he saw that whatever it was had a chimney.129 The whole was inscrutable, but the part gave it away.
Fig. 2.7 Hemisphere difference and the whole (Nikolaenko, 2001)
But once again, the failures of integrative processing where there is right-hemisphere damage are not confined to one domain or another, and are not part of the old visual/verbal dichotomy: difficulties experienced by patients with right-hemisphere lesions in grasping visuospatial information as a whole are related to difficulties they have in verbal-semantic understanding.130
Because of the way in which the left hemisphere is biased towards identification by parts, and the right hemisphere towards the whole picture, they also differ in the way they understand what they experience.
CONTEXT VERSUS ABSTRACTION
For the same reason that the right hemisphere sees things as a whole, before they have been digested into parts, it also sees each thing in its context, as standing in a qualifying relationship with all that surrounds it, rather than taking it as a single isolated entity.131 Its awareness of the world is anything but abstract.
Anything that requires indirect interpretation, which is not explicit or literal, that in other words requires contextual understanding, depends on the right frontal lobe for its meaning to be conveyed or received.132 The right hemisphere understands from indirect contextual clues, not only from explicit statement, whereas the left hemisphere will identify by labels rather than context (e.g. identifies that it must be winter because it is ‘January’, not by looking at the trees).133
This difference is particularly important when it comes to what the two hemispheres contribute to language. The right hemisphere takes whatever is said within its entire context.134 It is specialised in pragmatics, the art of contextual understanding of meaning, and in using metaphor.135 It is the right hemisphere which processes the non-literal aspects of language,136 of which more later. This is why the left hemisphere is not good at understanding the higher level meaning of utterances such as ‘it's a bit hot in here today’ (while the right hemisphere understands ‘please open a window’, the left hemisphere assumes this is just helpful supply of meteorological data). It is also why the right hemisphere underpins the appreciation of humour, since humour depends vitally on being able to understand the context of what is said and done, and how context changes it. Subjects with right brain damage, like subjects with schizophrenia, who in many respects resemble them, cannot understand implied meaning, and tend to take conversational remarks literally.
The left hemisphere, because its thinking is decontextualised, tends towards a slavish following of the internal logic of the situation, even if this is in contravention of everything experience tells us.137 This can be a strength, for example in philosophy, when it gets us beyond intuition, although it could also be seen as the disease for which philosophy itself must be the cure; but it is a weakness when it permits too ready a capitulation to theory. The left hemisphere is the hemisphere of abstraction,138 which, as the word itself tells us, is the process of wresting things from their context. This, and its related capacity to categorise things once they have been abstracted, are the foundations of its intellectual power. A patient with left-hemisphere damage described by Hécaen and de Ajuriaguerra, therefore relying on his right hemisphere only, on being asked to copy a model using pieces of wood appeared ‘as if compelled by some bizarre force to place the pieces of wood on top of the model that we were intending him to copy, rather than to one side’. This was thought to signify ‘a problem with the ability to produce an abstract representation from a concrete model’.139
The left hemisphere can only re-present; but the right hemisphere, for its part, can only give again what ‘presences’. This is close to the core of what differentiates the hemispheres. Hughlings Jackson, in many respects the father of modern neuropsychiatry, whose acute observations of patients with brain injury and epilepsy make him still a rich source of insight into hemisphere differences, intuited this as far back as the First World War. A patient of his had lost the power of expression in speech, but retained some automatic understanding of the names of objects, which Jackson presumed to be mediated by his right hemisphere. Although he could instantly pick up a brick on command, according to Jackson he could have no ‘memory’ of the word brick:
I do not believe that the man who cannot say (nor write) the word brick can be said to have a ‘memory’ of it (be conscious of the word itself). He has no consciousness of it, but of the thing it is a symbol of – a very different thing.140
Abstraction is necessary if the left hemisphere is to re-present the world. The left hemisphere operates an abstract visual-form system, storing information that remains relatively invariant across specific instances, producing abstracted types or classes of things; whereas the right hemisphere is aware of and remembers what it is that distinguishes specific instances of a type, one from another.141 The right hemisphere deals preferentially with actually existing things, as they are encountered in the real world.142 Because its language roots things in the context of the world, it is concerned with the relations betweenthings. Thus the right hemisphere does have a vocabulary: it certainly has a lexicon of concrete nouns and imageable words which it shares with the left hemisphere; but, more than that, perceptual links between words are made primarily by the right hemisphere.143
In general abstract concepts and words, along with complex syntax, are left-hemisphere-dependent. But, once again, the right hemisphere's language inferiority depends to a significant degree on positive inhibition by the left hemisphere. If the left hemisphere is sufficiently distracted, or incapacitated, the right hemisphere turns out to have a more extensive vocabulary, including long, unusual and non-imageable words.144
The contextual versus abstract distinction is illustrated by the different use of symbols by each hemisphere. In one sense of the word, a symbol such as the rose is the focus or centre of an endless network of connotations which ramify through our physical and mental, personal and cultural, experience in life, literature and art: the strength of the symbol is in direct proportion to the power it has to convey an array of implicit meanings, which need to remain implicit to be powerful. In this it is like a joke that has several layers of meaning – explaining them destroys its power. The other sort of symbol could be exemplified by the red traffic light: its power lies in its use, and its use depends on a 1:1 mapping of the command ‘stop’ onto the colour red, which precludes ambiguity and has to be explicit. This sort of symbolic function is in the realm of the left hemisphere, while the first type belongs to the realm of the right.145
In fact a particularly important difference lies in the right hemisphere's capacity to understand metaphor, which I will discuss in the next chapter. The right temporal region appears to be essential for the integration of two seemingly unrelated concepts into a meaningful metaphoric expression.146 Fascinatingly, however, clichéd metaphorical or non-literal expressions are dealt with in the left hemisphere: for such an expression, it is seeing the literal meaning of the hackneyed phrase that refreshes it, that requires insight (a bit like seeing a joke), and therefore in this case the non-salient (unfamiliar, because non-clichéd) meaning gets to be processed in the right hemisphere.147
INDIVIDUALS VERSUS CATEGORIES
At the same time it is the right hemisphere that has the capacity to distinguish specific examples within a category, rather than categories alone: it stores details to distinguish specific instances.148 The right hemisphere presents individual, unique instances of things and individual, familiar, objects, where the left hemisphere re-presents categories of things, and generic, non-specific objects.149 In keeping with this, the right hemisphere uses unique referents, where the left hemisphere uses non-unique referents.150 It is with the right hemisphere that we distinguish individuals of all kinds, places as well as faces.151 In fact it is precisely its capacity for holistic processing that enables the right hemisphere to recognise individuals.152 Individuals are, after all, Gestalt wholes: that face, that voice, that gait, that sheer ‘quiddity’ of the person or thing, defying analysis into parts.
Where the left hemisphere is more concerned with abstract categories and types, the right hemisphere is more concerned with the uniqueness and individuality of each existing thing or being. The right hemisphere's role as what Ramachandran has described as the ‘anomaly detector’ might in fact be seen rather as an aspect of its preference for things as they actually exist (which are never entirely static or congruent – always changing, never the same) over abstract representation, in which things are made to be fixed and equivalent, types rather than individuals.
The right hemisphere is concerned with finer discriminations between things, whether living or non-living.153 Indeed the cerebral principles of categorisation take this into account in a remarkable way. What is general and what is specific are, after all, relative. Thus characterising an object as a car, or a piece of fruit, is general; but as to what variety of fruit (pear), or in particular which kind of pear (comice), or what make of car (Citroën), particularly which model of Citroën (2CV), the matter is more specific.154 As the more ‘subordinate’ categories become more individuated they are recognised by the right hemisphere, whereas the left hemisphere concerns itself with the more general, ‘superordinate’ categories.155 In keeping with this, despite the well-known right-hemisphere advantage in dealing with the visuospatial, the left hemisphere is superior at identifying simple shapes and figures, which are easily categorised, whereas complex figures, being less typical, more individual, are better processed by the right hemisphere.156
In general, then, the left hemisphere's tendency is to classify, where the right hemisphere's is to identify individuals.157 But of course both hemispheres are involved in recognition according to the grouping of experience – how could it be otherwise? Each hemisphere must be able to make sense of reality by revealing a shape to what otherwise would be an amorphous mass of impressions. But how they do this in practice differs in vital respects which have a direct impact on the nature of the world that each brings into being. The right hemisphere's version is more global and holistic, based on the recognition of similarity with an ideal exemplar, and on where this is positioned in the context of other examples, whereas the left hemisphere identifies single features that would place the object in a certain category in the abstract.158 As a result, where the left hemisphere utilises abstract categories, the right hemisphere operates more effectively using specific exemplars.159 Functional imaging of the brain shows that the left hemisphere takes a ‘God's eye’, or invariant view, in its representation of objects, where the right hemisphere uses stored ‘real world’ views in order to group experience.160
The systematic categorising process of the left hemisphere can sometimes begin to have a life of its own. I have mentioned that networks of dopaminergic neurones are more widely distributed in the left hemisphere than the right. Excess dopaminergic transmission, which occurs in, for example, amphetamine abuse and in high-dose treatment with anti-Parkinsonian drugs, can mimic aspects of schizophrenia because it tends to favour the left hemisphere over the right. In such circumstances, a sort of freewheeling need to collect and categorise, coupled with the left hemisphere's over-riding concern with getting and making, is sometimes seen, known as ‘punding’ – the mechanical and repetitive assembling and disassembling of machines, collecting and categorising of inanimate objects, such as torches, TVs, stones, boxes, and so on.161 I once had a patient with schizophrenia who arranged and rearranged symmetrical structures of carefully collected commercial packaging: the resultant ‘sculptures’ filled his living room. On one occasion, after he had spent the weekend at his flat, I asked him how he had got on. He replied dryly: ‘I moved some things to the right’ – a response that has considerable interest in view of the left hemisphere's strong bias to attend to the right side of space, and disattend to the left (there is an asymmetry of hemispheric function in schizophrenia, with an abnormal but overactive left hemisphere compared with the right). The passion for collecting and organising is seen in other conditions, of course, including Asperger's syndrome, which also shows right-hemisphere deficits.
Don't think, though, that this categorising drive has a life of its own only in people who we regard as ill. It's at work all the time in all of us. As Henry Maudsley put it: we have
a sufficiently strong propensity not only to make divisions in knowledge where there are none in nature, and then to impose the divisions on nature, making the reality thus conformable to the idea, but to go further, and to convert the generalisations made from observation into positive entities, permitting for the future these artificial creations to tyrannise over the understanding.162
THE DIFFERENCES IN SAMENESS
The contrast between the differing world views of the two hemispheres is brought into focus in a remarkable way by the issue of sameness and difference. Again, seeing their handling of these as just different ‘comparator functions in information processing’ misses the point. They are not ‘functions’ within a world we already know to have a certain (mechanical) structure: they are themselves part of the foundations of the world in which we try to understand them.
An individual could be seen as a little universe, an infinite number of serial moments, experiences and perceptions (as the left hemisphere would see it), which are of course (at least as far as the right hemisphere is concerned) a single whole. Your wife or husband who left the house this morning may be in a different mood or have a different haircut by the evening, but this doesn't present a problem of identification, because these separate slices of experience, these separate frames of the film, as the left hemisphere would see it, are not really separate at all – they are the different aspects of one unique whole. But with certain right-hemisphere deficits, the capacity for seeing the whole is lost, and subjects start to believe they are dealing with different people. They may develop the belief that a person they know very well is actually being ‘re-presented’ by an impostor, a condition known, after its first describer, as Capgras syndrome.163 Small perceptual changes seem to suggest a wholly different entity, not just a new bit of information that needs to be integrated into the whole: the significance of the part, in this sense, outweighs the pull of the whole.
Fascinatingly, right-hemisphere deficit syndromes can result in something which looks like the opposite: the belief that someone one knows is duplicated in different places at different times. Not in other words the division of a unique whole, but the mass reproduction of one. ‘Something personal and usually alive has been duplicated as if it were a mere item on an assembly line,’ according to John Cutting, with loss of uniqueness and familiarity.164 A patient of mine accused her husband of two-timing because she believed she saw him on several occasions with different women while she was out in the town shopping, at times when she knew he should have been at work. This curious condition is called Fregoli syndrome, after an Italian quick-change artist of the early 1900s.165 Here the fine discrimination of individuals supplied by the right hemisphere is lost, and different individuals are lumped together and again ‘re-presented’ in a category.166 It is not the opposite of the Capgras syndrome, but a natural consequence of the same cause: a loss of the sense of a unique whole. Such ‘delusional misidentification’ applies not only to people, but to objects: another patient of mine began a vendetta against someone who, she believed, had entered her bedroom and subtly changed all her clothes for copies of a slightly inferior quality. It can even apply to places: one individual held that there were eight ‘impostor’ cities, duplicating his own, and said he had spent the last eight years wandering between them, without finding the real one. There were also eight duplicates of his wife and children, each duplicate living in a separate duplicate city with a double of the patient.167
Overall, then, and in keeping with the principle that it is not what is done, but how it is done, that distinguishes the two hemispheres, one cannot say that one hemisphere deals with single items (‘units’), and the other with aggregates. Both deal with ‘units’ and both deal with aggregates. Thus the right sees individual entities (units), and it sees them as belonging in a contextual whole (an aggregate), from which they are not divided. By contrast the left sees parts (units), which go to make up a something which it recognises by the category to which it belongs (an aggregate). However, the relationship between the smaller unit and the broader aggregate in either case is profoundly different: as is the mode of attention to the world with which it is associated.
THE PERSONAL VERSUS THE IMPERSONAL
Because the right hemisphere sees nothing in the abstract, but always appreciates things in their context, it is interested in the personal, by contrast with the left hemisphere, which has more affinity for the abstract or impersonal.168 The right hemisphere's view of the world in general is construed according to what is of concern to it, not according to objective impersonal categories, and therefore has a personal quality. This is both its strength and its weakness in relation to the left hemisphere. It deals preferentially with whatever is approaching it, drawing near, into relationship with it.169 The right temporal lobe deals preferentially with memory of a personal or emotionally charged nature, what is called episodic memory, where the left temporal lobe is more concerned with memory for facts that are ‘in the public domain’.170 Interestingly the right hemisphere's concern with the personal past may be directly linked to something else we will come to, its tendency towards feelings of sadness.171
THE LIVING VERSUS THE NON-LIVING
The great neurologist François Lhermitte drew attention thirty-five years ago to an essential difference between the hemispheres, when he described a case which confirmed that the right hemisphere is more concerned with living individuals than man-made objects.172 This flows naturally from its interest in whatever it is that exists apart from ourselves, and its capacity for empathy – as well as from its capacity to see the whole, where the left hemisphere sees an agglomerate of parts: there is an intuitive relationship between cutting things up and depriving them of life. It is the left hemisphere alone that codes for non-living things,173 while both hemispheres code for living things, perhaps because the living can be seen as independent individuals (right hemisphere) or as objects of use, prey, ‘things’, and so on (left hemisphere).174However, at least one study has found a clean divide between the hemispheres, the left coding for the non-living, and the right for the living, regardless of the task.175 Another study concluded that there are ‘different brain networks subserving the identification of living and nonliving entities’.176 Food, however, and musical instruments, presumably because of the intimate way in which they take part in the life of the body, sort with the living rather than the non-living. The body as such is a right-hemisphere entity, whereas body ‘parts’ are the province of the left hemisphere.177 In fact when the right hemisphere is no longer available to bring the left side of the body into being, the left hemisphere may substitute only a mechanical structure of inanimate parts down that side. One patient described by Ehrenwald reported that, following a right-hemisphere stroke,
‘where the left half of his chest, abdomen and stomach should be, he's got only a wooden plank.’ It goes right down to his anus, and is divided into compartments by transverse planks … food doesn't follow the usual path from the stomach through the intestines, ‘it gets sucked into the compartments of this scaffolding and it falls through the hole at the bottom of the framework’. All this is only on the left side. On the right the organs are all perfectly in place.178
And Ehrenwald records that it was not just a delusional idea, but a percept: he could see and feel the plank.
Not only does the right hemisphere have an affinity with whatever is living, but the left hemisphere has an equal affinity for what is mechanical. The left hemisphere's principal concern is utility. It is interested in what it has made, and in the world as a resource to be used. It is therefore natural that it has a particular affinity for words and concepts for tools, man-made things, mechanisms and whatever is not alive. The left hemisphere codes for tools and machines.179 References to tools and actions of grasping activate the left hemisphere even in left-handers, despite the fact that they habitually use the right hemisphere/left hand to grasp objects and use tools in daily life. And right-hemisphere damage leaves the ability to use simple tools unaltered, whereas left-hemisphere damage renders the sufferer incapable of using a hammer and nail, or a key and a padlock. However, right-hemisphere damage particularly impairs naturalistic actions involving a sequence of steps – for example, making a cup of coffee or wrapping a present.180
Could one go so far as to say that the left side represents science and the right side nature? Although I have myself expressed scepticism over the popular dichotomies associated with the two sides of the brain, I think there is a case for supposing that the left side represents the fruits of human invention, including language, manufacture and a partwise way of representing objects.181
So writes Michael Corballis, in the context of a tribute to Roger Sperry, both major contributors to our understanding of the hemispheres, and both alike sceptics of the ‘popular dichotomies’. He draws attention to the affinity of the left hemisphere for everything it has itself made (‘the fruits of human invention’) in contrast to the affinity of the right hemisphere for what exists before and after – and beyond – ourselves, namely nature. I would not accept the term ‘science’, in the true sense of the word, as applying to the left hemisphere; much of the spirit of empiricism comes from the right hemisphere, as I will suggest when considering scientific discovery during the period of the Renaissance, and science does not always proceed by predictable paths – it is more fortuitous, less controlled, than the left hemisphere thinks, and involves open awareness of what is.182 Perhaps Corballis would not accept it either, as he does not answer his own question. But if one were to substitute the word ‘mechanism’ – and, alas, so much science can be mechanistic – I would be in complete agreement.
The right temporal region appears to have areas not only specific for living things, but additionally for all that is specifically human.183 Such judgments of ‘humanness’ are separate from the right hemisphere's superior ability to recognise faces.184
The right hemisphere prioritises whatever actually is, and what concerns us. It prefers existing things, real scenes and stimuli that can be made sense of in terms of the lived world, whatever it is that has meaning and value for us as human beings.185 It is more able to assimilate information from the environment,186 without automatically responding to it, and, possibly as a result, the developing right hemisphere is more sensitive to environmental influences.187
At the same time the left hemisphere is more at home dealing with distorted, non-realistic, fantastic – ultimately artificial – images.188 This may be because they invite analysis by parts, rather than as a whole. But it does appear that the left hemisphere has a positive bias towards whatever is bizarre, meaningless or non-existent,189 though the data here are particularly hard to interpret because most studies have not sufficiently distinguished confounding elements.190
The fact that, while things are still ‘present’ in their newness, as individually existing entities – not ‘re-presented’ as representatives of a category – they belong to the right hemisphere, can be seen in the light of this distinction between the living and the non-living, since as they become over-familiar, inauthentic and therefore lifeless, they pass to the left hemisphere.
EMPATHY AND ‘THEORY OF MIND’
Because of the right hemisphere's openness to the interconnectedness of things, it is interested in others as individuals, and in how we relate to them. It is the mediator of empathic identification.191 If I imagine myself in pain I use both hemispheres, but your pain is in my right hemisphere.192 The same neurones in the right anterior cingulate cortex, an area known to be associated with the appreciation of pain, show activity whether we ourselves are hurt or we witness someone else undergoing a similar painful experience.193 ‘Self-awareness, empathy, identification with others, and more generally inter-subjective processes, are largely dependent upon … right hemisphere resources.’194 When we put ourselves in others' shoes, we are using the right inferior parietal lobe, and the right lateral prefrontal cortex, which is involved in inhibiting the automatic tendency to espouse one's own point of view.195 In circumstances of right-hemisphere activation, subjects are more favourably disposed towards others and more readily convinced by arguments in favour of positions that they have not previously supported.196
In general the right hemisphere is critical for making attributions of the content, emotional or otherwise, of another's mind, and particularly in respect of the affective state of another individual.197 According to Simon Baron-Cohen, the right hemisphere is engaged even in listening to words describing the mind, such as ‘think’ and ‘imagine’.198 But the right hemisphere will empathise with, identify with, and aim to imitate only what it knows to be another living being, rather than a mechanism – a point of interest in view of the roles we have seen the two hemispheres play in the division of the world into the animate and the inanimate.199 When we look at either a real hand or a ‘virtual reality’ hand grasping an object, we automatically activate the appropriate left-hemisphere areas, as if we too were grasping – but, strikingly, only in the case of the real, living hand do regions in the right temporoparietal area become activated.200 We have an unconscious, involuntary urge to imitate someone we are watching carrying out an action – so much so that, especially if it's something we've practised ourselves, the empathic entrainment is actually stronger than the voluntary desire to do something we'd like to see happen. But this is true only if we think it is a real person that's acting. If we think it's a computer, we just are not engaged.201
The right hemisphere plays an important role in what is known as ‘theory of mind’, a capacity to put oneself in another's position and see what is going on in that person's mind.202 This capacity emerges in primates along with self-recognition and self-awareness, and is closely linked to it.203 It is a capacity that children do not acquire fully until the age of four (though elements are probably present from 12 to 18 months), and which autistic children never acquire.204 The classic test for theory of mind shows two dolls, Sally and Anne, playing with a marble. They put it away in a box, and leave the room. While Sally is out, Anne returns, plays with the marble and puts it away in a different box. The question is: ‘When Sally returns, where will she look for the marble?’ Those without capacity for theory of mind indicate the new box where they know the marble to be, not the original one where Sally last saw it placed.205
The right hemisphere has by far the preponderance of emotional understanding.206 It is the mediator of social behaviour.207 In the absence of the right hemisphere, the left hemisphere is unconcerned about others and their feelings: ‘social intercourse is conducted with a blanket disregard for the feelings, wishes, needs and expectations of others.’208 Patients with right frontal deficits, but not left frontal deficits, suffer a change of personality whereby they become incapable of empathy.209
Considerable interest has been raised by the discovery that there are neurones, nicknamed ‘mirror neurones’, which are active both when we do something and when we watch others do it.210 Physiological and behavioural evidence indicated that the left pars opercularis (part of Broca's area), the area of the frontal lobe critical for speech production, contains mirror neurones which are involved in the imitation of finger movements.211 So absorbing was this finding – which is indeed highly significant, and which I will discuss in the next chapter – that it was until recently thought that mirror neurones were a speciality of the human left hemisphere, and their existence has even been put forward as a reason for language's having developed in the left hemisphere, rather than the right.212 But that seems a bit like putting the cart before the horse, especially since both the left and right pars opercularis equally have mirror neurones, and both hemispheres contribute to the processing of watching and imitating.213 In fact, which hemisphere is involved on any one occasion has not only to do with what and where the action is that we are copying, but also with how instrumental (‘object-directed’) that action is. Such actions excite the left hemisphere's system. On the other hand, the predominant contribution to the imitation of actions that are non-instrumental comes from the right temporal and frontal lobes.214
Mirror neurones are a means of understanding another's intentions, amongst other things, and are not just about copying actions.215 They form part of our capacity to understand others and empathise with them. For instance, in imitating other people's facial expressions, it is the right pars opercularis, with its mirror neurones, which is the critically important area; and it is this area that appears to be silent in autistic children when carrying out such a task.216
The affinity of the right hemisphere with emotions and the bodily experience of them is reflected in a range of functional asymmetries. Part of the right frontal pole of the brain, the so-called orbitofrontal cortex of the right hemisphere, is essential to emotional understanding and regulation.217 It is also where the emotional significance of events is consciously appreciated.218 The right hemisphere is in general more intimately connected with the limbic system, an ancient subcortical system that is involved in the experience of emotions of all kinds, and with other subcortical structures, than is the left hemisphere.219 The right frontal pole also regulates the hypothalamic-pituitary axis, which is the neuroendocrine interface between the body and emotion,220 and is essential to our subjective appreciation of the body's physiological condition.221 It is intimately connected with the unconscious and automatic systems for regulating the body and its level of arousal, for example through the autonomic control of heart rate or neuroendocrine function.222 As a consequence it is also the right frontotemporal cortex that exerts inhibitory control over emotional arousal.223
Although there has been much debate about the particular emotional timbre of each hemisphere (of which more shortly), there is evidence that in all forms of emotional perception, regardless of the type of emotion, and in most forms of expression, the right hemisphere is dominant.224
It is the right hemisphere that identifies emotional expression: it is faster and more accurate than the left hemisphere in discriminating facial expression of emotion.225 Specifically the right superior temporal sulcus appears to be involved in recognition of facial emotion.226 The right hemisphere is the locus of interpretation, not only of facial expression, but of prosody (vocal intonation) and gesture.227 The superiority for emotional perception is in addition to, and distinct from, the right parietal lobe's known superiority for visuospatial interpretation.228 Those with right-hemisphere damage have difficulty understanding emotional intonation or implication.229
Curiously it seems that the left hemisphere reads emotions by interpreting the lower part of the face. Though the left hemisphere can understand emotional display, it looks not at the eyes, even when directed to do so, but at the mouth.230 The right hemisphere alone seems to be capable of understanding the more subtle information that comes from the eyes. Empathy is not something one reads in the lower face, where relatively blunt messages – friend or foe – tend to be conveyed. A patient of mine with a right temporoparietal deficit asked me ‘What's all this with the eyes?’ When I asked what she meant, she explained that she had noticed people apparently communicating coded messages with their eyes, but could not understand what they were, presumably because the part of her brain that would have interpreted it was no longer functioning – further grounds for paranoia in those who have to rely on their left hemisphere to constitute the world.
When it comes to the understanding (and expression) of emotion in language, again, despite left-hemisphere preponderance for language, the right hemisphere is superior.231 Emotional language may be possible even when speech is lost through a left-hemisphere stroke.232 It is the right hemisphere that understands the emotional or the humorous aspect of a narrative.233 Memory for emotional language is in the right hemisphere.234 Ultimately there is clear evidence that when it comes to recognising emotion, whatever it may be, whether it is expressed in language or through facial expression, it is the right hemisphere on which we principally rely.235
The face is the common mediator of two of the most significant aspects of the right hemisphere's world: the uniqueness of the individual and the communication of feeling. The right hemisphere is involved in identifying not just the facial expression of emotion, but the emotion as it relates to an individual face.236 This begins in children and is the principle medium for the child's growing sense of identity, through interaction with the mother's face.237 It is also in the right parietotemporal cortex that the child appreciates the mother's voice.238
Because of its concern with our embodied selves, our feelings, and the feelings and intentions of others, as well as their uniqueness, it could be anticipated that it is through the right hemisphere that emotional faces are stored in memory.239 In fact it is the right hemisphere that is principally responsible for our ability to identify and remember faces at all.240 The capacity would seem to us quite extraordinary if we were not so close to it and so familiar with it. Faces are broadly similar complex three-dimensional structures that have to be distinguished from one another by often minutely differing interrelations amongst the ‘parts’ of the whole (which, nonetheless, can change with facial expression from second to second), and individually discriminated in differing orientations, at varying distances, in different lighting conditions, often while moving, and in a fraction of a second. It is amazing that we can do it at all. An inability to recognise faces is called prosopagnosia, and follows right-hemisphere lesions.241
What the right hemisphere crucially appears to be able to do here is to see the ‘configurational’ aspects of the whole. In prosopagnosia, this capacity is lacking.242 In fact, in its absence the left hemisphere has to rely on the laborious process of trying to put the face together from the parts, with the paradoxical effect that it may find it no easier to recognise a face the right way up than upside down, and may even find it easier upside down, because such views force a concentration on the parts.243
There is a critical role here for the right middle fusiform gyrus,244 but latterly it has become clear that the network underlying facial recognition is broadly distributed in the right hemisphere.245 Right-brain-damaged patients are not only poorer at identifying faces, compared with left-brain-damaged patients, but are poor at assessing such features as the age of a face with which they are not familiar.246 The right hemisphere is pre-eminent, not only in identifying an individual human face, and in interpreting its emotional expression, but in appreciating its age, sex, and attractiveness.247
It was one of Wigan's achievements to have recognised prosopagnosia in 1844,248 but it took another hundred years for it to be given a name. In 1947 Joachim Bodamer described a patient who reported that faces seemed to him ‘strangely flat, white with emphatic dark eyes, as if made from a flat surface, like white oval plates, all alike’.249 The lack of depth is very interesting for reasons I will come to. Prosopagnosia was linked to right-hemisphere lesions by Sergent and Villemure, who recognised that there was ‘an inability to combine the component features into a configurational facial representation that would uniquely define each face’.250 Putting together the parts could not achieve a unique whole.
It is also remarkable that once again there is a specific defect for recognition of eyes. In some cases, presumably because the left hemisphere, with its interest in the lower part of the face, steps into the breach, subjects with partial prosopagnosia following a right-hemisphere lesion have been able to glean evidence from the mouth area, but were quite unable to use information from the eyes.251
The superiority of the right hemisphere for recognising faces is yet another lateralised difference that goes a considerable way down the evolutionary chain – for example, it is even present, believe it or not, in sheep, who can remember individual human and sheep faces after a gap of years, again relying principally on the right hemisphere.252
As well as emotional recognition, the right hemisphere plays a vital role in emotional expression,253 via the face or the prosody of the voice.254 The right frontal lobe is of critical importance for emotional expression of virtually every kind through the face and body posture.255 The one exception to the right hemisphere superiority for the expression of emotion is anger.256 Anger is robustly connected with left frontal activation.257 Aggression is motivating and dopamine plays a crucial role in the rewards it offers.258
Autistic children, who cannot understand social language, irony and metaphor, and lack capacity for empathy – all mediated by the right frontal region – lack prosodic skill, the ability to convey meaning and feeling through intonation and inflection of the voice.259
It is the right hemisphere that mediates spontaneous facial expressions in reaction to humour or other emotions, including smiling and laughter.260 It is also the right hemisphere that is responsible for the peculiarly human ability to express sadness through tears.261
The left half of the face (or ‘hemiface’), which is controlled by the right hemisphere, is more involved in emotional expression.262 Emotions are also more strongly perceived when expressed by the left hemiface:263 and, intriguingly, the left hemiface is also larger than the right in right-handers.264 Although facial expression of emotion is a human universal, there are, inevitably, differences in facial expression across cultures; and because of the very fact that the left hemiface displays more complex emotional information, being able to convey mixed feelings, it seems that it may be easier in cross-cultural situations for people to read the relatively simple information conveyed by the right hemiface.265
This specialisation of the right hemisphere for emotion is a process which begins in pre-human species: chimpanzees and some other non-human primates show, just as we do, right-hemisphere specialisation for facial expression of emotions.266
The right hemisphere's affinity for both the perception and expression of emotion appears to be confirmed by the strong universal tendency to cradle infants with their faces to the left, so that they fall within the principal domain of attention of the adult's right hemisphere, and they are exposed to the adult's own more emotionally expressive left hemiface.267 This preference is known to go back at least 2,000–4,000 years,268 and even left-handed mothers display the leftward cradling bias.269 In fact even chimpanzees and gorillas show the same leftward bias for cradling their infants.270
DIFFERENCES IN EMOTIONAL AFFINITY
It is the right hemisphere which gives emotional value to what is seen, a topic I will return to later, in considering the way in which the hemispheres influence the meaning we find in the experiential world.271 In the absence of a functioning right hemisphere our world and our selves become emotionally impoverished. The right frontal lobe plays a supremely important part in personality – in who we fundamentally are.272
Nonetheless the left hemisphere does play a role in the understanding and expression of emotion. What are the differences?
It seems, for a start, that the left hemisphere specialises in more superficial, social emotions, by contrast with the right hemisphere, which is more directly in touch with primary-process emotionality.273 Related to this, the left hemisphere may also be more involved in conscious representation of emotion: willed, or forced, emotional expressions, once again principally of the mouth area, are controlled by the left hemisphere.274 A study on conscious and unconscious processing of emotional facial expression has suggested that the left but not the right amygdala is associated with explicit representational content of the observed emotion, whereas the right amygdala is more closely involved with unconscious emotional processing.275
It has to be said that, though it is involved with emotion, the left hemisphere remains, by comparison with the right, emotionally relatively neutral,276 something which is evidenced by its affinity for ‘non-emotional’, abstract paintings.277 Emotional stimuli are not incorporated into mood – not adopted personally – when offered to the left hemisphere rather than the right.278 The whole business seems more conscious, more willed, more deliberate, and that is in keeping with the left hemisphere's need to influence and manipulate, as well as its role in re-presenting experience. In alexithymia, a condition of lack of awareness or capacity to express emotional arousal in words, the problem arises from an inability of the emotionally aware right hemisphere, which can be shown to be experiencing emotional arousal, to communicate it to the left hemisphere.279
The literature also suggests that there may be differences in the emotional timbre of the hemispheres, and this is a complex area.280 Old ideas that the right hemisphere was concerned with so-called ‘negative’ emotions and the left hemisphere with ‘positive’ emotions are not substantiated; a prevailing theory is that right-hemisphere emotions are those of ‘withdrawal’, and left-hemisphere emotions those of ‘approach’. Neither seems to me very satisfactory. Some broad agreement exists that the right hemisphere is more in tune with sadness, and less with anger, than the left hemisphere;281 and that what we call ‘positive’ emotions rely on both.282 While the right hemisphere is associated with positive affect in many cases,283 and may even be the principle source of pleasurable experience,284 it is in general the left hemisphere that tends to take a more optimistic view of the self and the future.285 In fact there is evidence, which I shall come to, that it may take an unwarrantedly optimistic view. Once again the right hemisphere's range is more inclusive (it can deal with either), and the left hemisphere's more partial. It seems to me a possibility that those emotions which are related to bonding and empathy, whether we call them ‘positive’ or ‘negative’, are preferentially treated by the right hemisphere, as one would expect: such stimuli capture right-hemisphere attention.286 By the same token, those to do with competition, rivalry and individual self-belief, positive or negative, would be preferentially treated by the left hemisphere.287
Another thought-provoking detail about sadness and the right hemisphere involves the perception of colour. Brain regions involved in conscious identification of colour are probably left-sided, perhaps because it involves a process of categorisation and naming;288 however, it would appear that the perception of colour in mental imagery under normal circumstances activates only the right fusiform area, not the left,289and imaging studies, lesion studies and neuropsychological testing all suggest that the right hemisphere is more attuned to colour discrimination and perception.290 Within this, though, there are hints that the right hemisphere prefers the colour green and the left hemisphere prefers the colour red (as the left hemisphere may prefer horizontal orientation, and the right hemisphere vertical – a point I shall return to in considering the origins of written language in Chapter 8).291 The colour green has traditionally been associated not just with nature, innocence and jealousy but with – melancholy: ‘She pined in thought, / And with a green and yellow melancholy / She sat like Patience on a monument, / Smiling at grief’.292
Is there some connection between the melancholy tendencies of the right hemisphere and the mediaeval belief that the left side of the body was dominated by black bile? Black bile was, of course, associated with melancholy (literally, Greek melan-, black + chole, bile) and was thought to be produced by the spleen, a left-sided organ. For the same reasons the term spleen itself was, from the fourteenth century to the seventeenth century, applied to melancholy; though, as if intuiting that melancholy, passion, and sense of humour all came from the same place (in fact the right hemisphere, associated with the left side of the body), ‘spleen’ could also refer to each or any of these.
The issue of the relationship between depressive illness and the right hemisphere is complex. Here more than anywhere one has to take into account the influence of the anterior–posterior (‘front–back’) axis of the brain, as well as the right–left axis. It seems that the polarity of emotional timbre between the two hemispheres is specifically tied to the most highly and lately evolved, most ‘human’ parts of the brain, the frontal lobes. Left anterior lesions are associated with depression, and right anterior lesions associated with ‘undue cheerfulness’.293 The closer the left-hemisphere lesion lies to the frontal pole, the greater the depressive symptomatology.294 For those with right-hemisphere lesions the converse is true: the more caudal (the further back) the lesion, the greater the chance of depression.295 This confluence of evidence suggests that the right frontal pole has a depressive stance compared with either the left frontal pole or its own parieto-occipital cortex.296 Depression per se is probably associated with reduced right posterior activity in addition to increased right frontal activity in most cases,297 although as one might predict threat monitoring is a right-posterior activity.298 There is evidence of left-hemisphere over-activity in mania,299the polar opposite of depression, and this may also obtain in other mammals.300
Lesion studies confirm the relationship between activity of the right frontal lobe and depression,301 and neuroimaging studies also suggest a correlation between left frontal hypofunction and depression.302Greater right than left activation is related to depressed mood.303 Specifically increased electrical activity in the right-prefrontal region is a marker of depression,304 and the majority of EEG studies also confirm left frontal hypoactivation.305 In normal subjects relative right-sided EEG activation at rest predicts greater experience of ‘negative’ affect: subjects with relatively greater left-frontal activation at rest ‘may be able quickly to terminate their reaction, while subjects with right-frontal activation may lack the requisite coping skills to minimise the duration of the negative affective response’.306 Depressives relatively favour the left visual field and make more eye movements to the left in ways that have been validated to suggest right-hemisphere activation.307
Confirmatory evidence comes from treatment for depression. The decreased left anterior functioning found in depression remits, as expected, with the illness. Where the blood flow in the left anterior frontal region is initially more sharply decreased, this predicts a better response to antidepressants.308 Depression is less likely to resolve or respond to treatment where there are irreversible lesions in the left hemisphere (but not other brain areas).309
There is also evidence that the types of depression experienced in right posterior hypoactivity are different from those experienced in left frontal hypoactivity, in ways which are in keeping with the views of the worlds that the two hemispheres bring into being. Thus depression resulting from damage to the right hemisphere has more of indifference or apathy – a global, vague lifelessness – in contrast to the anxious, disturbed depression, accompanied by biological features, resulting from lesions to the left hemisphere.310 The sort of anxiety that accompanies depressed mood, and could be induced by reading a sad narrative, is known as anxious arousal, and shows greater lateralisation to the right hemisphere. By contrast anxious apprehension, based as it is on a fear of uncertainty and lack of control – preoccupations of the left hemisphere – is accompanied by preferential left hemisphere activation.311
In interpreting all neuroimaging studies of emotion, one should bear in mind the strictures of Jaak Panksepp, probably the world's most distinguished neuroscientist of affect and emotion, that we are more likely to be imaging the areas associated with the cognitive content of an affective state than those associated with the pre-cognitive affective state itself.312
REASON VERSUS RATIONALITY
Despite the right hemisphere's overwhelmingly important role in emotion, the popular stereotype that the left hemisphere has a monopoly on reason, like the view that it has a monopoly on language, is mistaken. As always it is a question not of ‘what’, but of ‘in what way’.
In fact reasoning is of different kinds, and though linear, sequential argument is clearly better executed by the left hemisphere, some types of reasoning, including deduction, and some types of mathematical reasoning, are mainly dependent on the right hemisphere. More explicit reasoning is underwritten by the left hemisphere, less explicit reasoning (such as is often involved in problem solving, including scientific and mathematical problem solving) by the right hemisphere.313 There is a relation between the pleasurable ‘aha!’ phenomenon of insight and the right amygdala, which mediates interactions between emotions and higher frontal cognitive function.314 In fact an extensive body of research now indicates that insight, whether mathematical or verbal, the sort of problem solving that happens when we are, precisely, not concentrating on it, is associated with activation in the right hemisphere, mainly in the right anterior temporal area, specifically in the right anterior superior temporal gyrus, though where there are high levels of restructuring involved there is also activity in the right prefrontal cortex.315 Insight is also a perception of the previous incongruity of one's assumptions, which links it to the right hemisphere's capacity for detecting an anomaly.
Problem solving, making reasonable deductions, and making judgments may become harder if we become conscious of the process. Thus rendering one's thought processes explicit, or analysing a judgment, may actually impair performance, because it encourages the left hemisphere's focus on the explicit, superficial structure of the problem.316
The evidence is that mathematical skills are divided between the hemispheres. Some studies have shown mathematical performance to be impaired worse in children317 and in adults318 with left-hemisphere, than with right-hemisphere, damage. However, in another study left-hemisphere-damaged children were significantly poorer only at written language, while right-hemisphere-damaged children performed worse on written language, reading and maths.319 The right hemisphere clearly does play a role in arithmetical calculations,320 and, in general, mathematical calculations activate more strongly on the right.321 Addition and subtraction activate the right parietal lobe, whereas multiplication activates verbal remembrance of ‘times tables’ in the left hemisphere.322 Calculating prodigies appear to use more right-hemisphere-dependent strategies, making use of episodic memory.323
The right hemisphere appears to be crucially involved in the process of deductive reasoning, a process which is independent not only of left-hemisphere language areas, but also of right-hemisphere visuospatial areas: for example, even in the absence of any correlated visual input (e.g. where problems are presented acoustically via headphones), different types of reasoning problems evoke activity in the right superior parietal cortex, and bilaterally in the precuneus.324 That the precuneus is involved is in itself interesting, because the precuneus, a centre that lies deep inside the parietal lobe, is deeply connected both with emotion – it forms part of the limbic system – and the sense of the self. It is one of the brain's most consistently ‘hot’ spots, with a high resting metabolic rate, and it goes quiet in altered states of consciousness where the sense of self is no longer active, such as sleep, anaesthesia and vegetative states. It seems to play an important role in episodic memory, which is critical for personal identity, and in adopting the first person perspective.325 And in fact deductive logic is also associated with the right ventromedial prefrontal area of the brain, an area known to be devoted to emotion and feeling.326 Seeing what follows from a social, emotional understanding of the situation in which one finds oneself in the real world is at least as important, then, as seeing what follows from an abstract proposition.
One finding that might seem at first sight unexpected, but the full significance of which will become apparent only in the next chapter, is that it is the right hemisphere that has the intuitive sense of numbers and their relative size. However, the sense is approximate and does not have precision. The left hemisphere, by contrast, has precision, but it has no intuitive sense of what it is actually doing, other than following rules and manipulating symbols.327 If one acquires a computational skill leading to a precise answer, it will be most evident in the language in which it was acquired: there is no such language effect in relation to inexact estimation, the intuitive sense of size.328
It is worth considering that numbers can either signify absolutes – a quantifiable amount, as in statistics – which would suggest an affinity with the left hemisphere, or signify relations, which would suggest an affinity with the right hemisphere. For Pythagoras, it was this regularity of proportion or relationship, rather than number in any absolute sense, that underpinned music and beauty – the music of the spheres, the natural harmony of the universe.
THE TWIN BODIES
Emotion is inseparable from the body in which it is felt, and emotion is also the basis for our engagement with the world. Social understanding in the sense of empathic connection, as well as understanding how others feel, what they mean not only by what they say in context, as we have seen, but by their facial expressions, their ‘body language’ and tone of voice – all this is made possible by the right hemisphere.
In keeping with its capacity for emotion, and its predisposition to understand mental experience within the context of the body, rather than abstracting it, the right hemisphere is deeply connected to the self as embodied. Although each side of the brain has both motor and sensory connections with the opposite side of the body, we know that the left hemisphere carries an image only of the contralateral (right) side of the body – when the right hemisphere is incapacitated, the left part of the individual's body virtually ceases to exist for that person. It is only the right parietal lobe that has a whole body image.329 Importantly this body image is not just a picture. It is not a representation (as it would be if it were in the left hemisphere), or just the sum of our bodily perceptions, or something imagined, but a living image, intimately linked to activity in the world – an essentially affective experience.330 Which is why disturbances in it lead to profoundly disturbing illnesses, such as body dysmorphia and anorexia nervosa.331
More than this, the right and left hemispheres see the body in different ways. The right hemisphere, as one can tell from the fascinating changes that occur after unilateral brain damage, is responsible for our sense of the body as something we ‘live’, something that is part of our identity, and which is, if I can put it that way, the phase of intersection between our selves and the world at large. For the left hemisphere, by contrast, the body is something from which we are relatively detached, a thing in the world, like other things (en soi, rather than pour soi, to use Sartre's terms), devitalised, a ‘corpse’.332 As Gabriel Marcel puts it, it is sometimes as if I am my body, sometimes as if I have a body.333 Some languages, such as German, see the body in these two senses as so distinct that they have different words for them: Leib for the first, Körper for the second. Incidentally the German word Körper, related to the English ‘corpse’, came into the language through medicine and theology (the body there being the element left when the soul departed); the word Leib, related to leben/lebendig (English ‘live/alive’) referred to the ‘bodies’ that survived a battle – those who were not Körper. In fact even more striking is that the Greek word which subsequently came to indicate the body considered separately from the person, so-ma, is never used in Homer to refer to the living body, only to a corpse.334
The left hemisphere appears to see the body as an assemblage of parts: remember the patient of Ehrenwald's, whose body became rectilinear, compartmentalised, inanimate and hollow (an assemblage of scaffolding) following a right-hemisphere stroke. If the right hemisphere is not functioning properly, the left hemisphere may actually deny having anything to do with a body part that does not seem to be working according to the left hemisphere's instructions. Patients will report that the hand ‘doesn't belong to me’ or even that it belongs to the person in the next bed, or speak of it as if made of plastic.335 One patient complained that there was a dead hand in his bed. A male patient thought the arm must belong to a woman in bed with him; a white woman thought hers belonged to ‘un petit nègre’ in bed with her; another complained that there was a child in the bed, on his left. Yet another was convinced that the nurses had bundled up his arm with the dirty laundry and sent it away to be washed.336
One patient believed quite firmly that the paralysed arm belonged to her mother, though in all other respects her conversation was quite normal.337 The process in her case was, typically, reversed by inhibiting the left hemisphere, by a process called vestibular stimulation:
Whose arm is this?
It's not mine.
Whose is it?
It's my mother's.
How on earth does it happen to be here?
I don't know. I found it in my bed.
How long has it been there?
Since the first day. Feel, it's warmer than mine. The other day too, when the weather was colder, it was warmer than mine.
So where is your left arm?
(makes an indefinite gesture forwards) It's under there. Immediately after vestibular stimulation [inhibiting the left hemisphere], the examiner asks the patient to show her the patient's left arm.
(points to her own left arm) Here it is.
(raises the patient's left arm) Is this arm yours?
Where is your mother's arm?
(hesitates) It is somewhere about.
I don't know. Perhaps here, under the bedclothes. (She looks to her right, under the bedclothes.)
Two hours after vestibular stimulation AR is questioned again by the examiner.
(points to the patient's left arm) Whose arm is this?
It's my mother's. It's warmer.
Where is your left arm?
AR stares silently at the examiner. One hour and a half later, she spontaneously addresses the examiner.
(points to her left arm) My mother's arm is colder than it was this morning. Feel how cold it is.
On the following morning (30 November), the examiner asks AR again whose is AR's left arm, while pointing to it.
It's my mother's. It's pretty warm. I found it here. She forgot it when she was discharged from the hospital.
After vestibular stimulation performed according to the same procedure used the day before, the examiner raises the patient's left arm and asks once again whose arm it is.
(touches her left arm) It's mine.
Examiner: Where is your mother's arm?
It must be here, in the corner. (She looks for her mother's arm under the bedclothes without finding it.) It's pretty warm. It is a strong arm; my mother was a laundress …
This is known as asomatognosia, and it often follows right-hemisphere stroke.338 A lack of capacity to recognise parts of the embodied self is always associated with right-hemisphere damage, never with left-hemisphere damage.339 The phenomenon can be replicated by selectively anaesthetising the right hemisphere.340
It can also give rise to the belief that the affected part is under alien control. A patient described by Lhermitte showed no concern and was positively euphoric, despite being paralysed down his left side: ‘it seemed as if the entire left-hand side of his body had disappeared from his consciousness and from his psychic life’. Three days later, however,
this patient reports that from time to time an alien hand, which disturbs and annoys him, comes and places itself on his chest: he says ‘this hand presses on my tummy and chokes me’. ‘This hand bothers me’, he says again, ‘it doesn't belong to me, and I'm afraid it might thump me.’
He thought it might belong to the man in the next bed.341 Another patient came to believe that the left side of his body was ‘evil’ and controlled by external agents, perhaps by the devil in collusion with his dead father.342
There is greater proprioceptive awareness in the right hemisphere than the left: that is to say, the right hemisphere knows better than the left, without having to look, where for example the contralateral hand is and what position it adopts – even though that favours the left hand in right-handers.343 The right hemisphere is far more closely linked to the physiological changes that occur in the body when we experience emotion.344 The right hemisphere's superiority in the emotional realm is explicitly linked to this close physiological relationship with the body.345 This is a further reason why we hold babies to the left: ‘the emotional impact of touch, the most basic and reciprocal mode of interaction, is also more direct and immediate if an infant is held to the left side of the body’.346 Although studies of the effects of stroke on sexual function have shown it to be worse following left-hemisphere stroke, this is confounded by depression, a common sequel of left-hemisphere stroke; if depressed subjects are excluded it appears to be more dependent on the right hemisphere.347
Interestingly, when there is right hemisphere damage, there appears to be a removal of the normal integration of self with body: the body is reduced to a compendium of drives that are no longer integrated with the personality of the body's ‘owner’. This can result in a morbid and excessive appetite for sex or food, which is out of keeping with the nature of the individual involved.348
I drew attention earlier to the fact that the right hemisphere is more intimately connected with the unconscious and automatic systems for regulating the body and its level of arousal, for example through the autonomic control of heart rate or neuroendocrine function (see pp. 58–9 above). There is one exception to this. There are two ‘opponent processors’ within the autonomic nervous system, the sympathetic and the parasympathetic systems. There is some evidence that, whereas sympathetic nervous control is more influenced by the right hemisphere, control of the parasympathetic nervous system is more under left-hemisphere control.349 Of the two, the sympathetic is more important for modulating heart rate and blood pressure in response to emotion.350 It is also more involved with response to the new, the uncertain, and the emotionally demanding, the special domains of the vigilant right hemisphere, whereas the parasympathetic nervous system produces relaxation of autonomic function, appropriate to the familiar, the known and the emotionally more neutral, the special domains of the left hemisphere. But release of the left hemisphere can certainly increase activity inappropriately, and will be associated with sympathetic activity. Perhaps the safest conclusion is that this area remains unclear.
MEANING AND THE IMPLICIT
When we think of meaning we tend to think of language, and the left hemisphere's great contribution to meaning is language, symbol manipulation. So great is it that I will devote the next chapter to examining the significance of this alone. The left hemisphere has a much more extensive vocabulary than the right, and more subtle and complex syntax. It extends vastly our power to map the world and to explore the complexities of the causal relationships between things.
This superiority has nothing to do with a greater affinity for auditory material. For one thing, music is in most respects better appreciated by the right hemisphere (see below). To the extent that there is an auditory superiority for language in the left hemisphere, it is in any case due to its inhibitory effect on the right hemisphere.351 Rather the superiority for language stems from its nature as the hemisphere of representation, in which signs are substituted for experience. If it were not for this, one might have expected sign language, which is visuospatial rather than verbal in nature, to be dealt with in the right hemisphere. But, despite that, sign language is left-hemisphere-mediated;352 and disturbances of sign language in deaf subjects are also consistently associated with left-hemisphere damage, the resulting deficits being typically analogous to the language problems experienced by hearing subjects with a lesion in the same location.353 This proves that the specialisation of what is called the auditory cortex is not to do with the processing of auditory material, or even of words themselves. It is to do with the processing of signs, tokens, representations of things, whether these be verbal or visuospatial. And, equally, the supposed visuospatial bias of the right hemisphere is probably not about visuospatial qualities in themselves, but because this is the main route of perception of the external world, of things in and of themselves, as opposed to their signs.
But the left hemisphere is attached to language per se: language is where it is at home. It seems to be (in an interesting parallel with the situation regarding numbers mentioned above) actually less concerned about meaning than the right hemisphere, as long as it has control of the form and the system. In conditions of right-hemisphere damage, where the left hemisphere is no longer under constraint from the right, a meaningless hypertrophy of language may result.354
Once again the stereotypes are wrong. The left hemisphere may have a lot to do with language, but the right hemisphere plays a vital part in language, too. It uses language not in order to manipulate ideas or things, but to understand what others mean. This ‘silent’ hemisphere recognises words,355 and has vocabulary, as discussed above, and even some aspects of syntax.356 In fact not just language reception, but expression, too, is highly right-hemisphere-dependent: the verbal expression problems of right-hemisphere-damaged patients can be severe, and it has been suggested that they are almost as severe as those of left-hemisphere-damaged patients.357
And, as far as comprehension goes, they are in some respects worse. The right hemisphere's particular strength is in understanding meaning as a whole and in context. It is with the right hemisphere that we understand the moral of a story,358 as well as the point of a joke.359 It is able to construe intelligently what others mean, determining from intonation, and from pragmatics, not just from summation of meaning units, subject to the combinatorial rules of syntax, as a computer would.360 It is therefore particularly important wherever non-literal meaning needs to be understood – practically everywhere, therefore, in human discourse, and particularly where irony, humour, indirection or sarcasm are involved.361 Patients with right-hemisphere damage have difficulty understanding non-literal meaning.362 They have difficulty with indirect meaning, such as is implied by metaphor363 and humour.364 In fact, those with right-hemisphere damage cannot make inferences, an absolutely vital part of understanding the world: they do not understand implicit meanings whatever their kind, but detect explicit meanings only.365 (Once an inference is made and begins to be more explicit, the process can be transferred from the right superior temporal gyrus to the left.)366 While syntactical performance is more impaired in left-hemisphere-damaged children, actual lexical understanding is worse impaired by right-hemisphere damage.367
The full significance of the left hemisphere's incapacity for, and the right hemisphere's affinity for, metaphor will become clear in the next chapter. While it does, certainly, mean that understanding of the indirect, connotative language of poetry depends on the right hemisphere, the importance of metaphor is that it underlies all forms of understanding whatsoever, science and philosophy no less than poetry and art.368
The right hemisphere specialises in non-verbal communication.369 It deals with whatever is implicit, where the left hemisphere is tied to ‘more explicit and more conscious processing’.370 Subtle unconscious perceptions that govern our reactions are picked up by the right hemisphere. For example, it is the area around the fusiform gyrus of the right hemisphere that is dominant for unconscious reading of facial expressions.371 Emotional shifts that are expressed in minute facial changes are mirrored and synchronously matched by the observer's right hemisphere within 300-400 milliseconds, at levels beneath awareness.372 Looking at the movements of another's eyes and mouth activates the right posterior temporo-occipital cortex.373 It will be remembered that the left hemisphere does not attend to the eyes: this is one reason why the right hemisphere is better at detecting deceit.374 Because the right hemisphere picks up subtle clues and meanings, and because it can understand how others are feeling and thinking, we rely on it when we judge whether people are lying.375 Those with right-hemisphere damage have difficulty distinguishing jokes from lies; by contrast those with left-hemisphere damage are actually better at detecting a lie than normal individuals, another instance of the way in which the hemispheres require separation as much as connection.376 I am reminded of an observation of John Napier's about the relationship between lying and explicit versus implicit communication: ‘If language was given to men to conceal their thoughts, then gesture's purpose was to disclose them.’377
The realm of all that remains, and has to remain, implicit and ambiguous is extensive, and is crucially important. This is why one feels so hopeless relying on the written word to convey meaning in humanly important and emotionally freighted situations.
Non-verbal behaviour, language, facial expression, intonations and gestures are instrumental in establishing complex contradictory, predominantly emotional relations between people and between man and the world. How frequently a touch by the shoulder, a handshake or a look tell more than can be expressed in a long monologue. Not because our speech is not accurate enough. Just the contrary. It is precisely its accuracy and definiteness that make speech unsuited for expressing what is too complex, changeful and ambiguous.378
As we have seen, things that are value-laden for me, because of their place in ‘my’ world, are salient to the right hemisphere, a consequence of its concern for what has personal meaning. The ‘I’, here, is a social being, however, not an objectified isolated entity, since the right hemisphere mediates social behaviour in all its ramifications. This is why a right-hemisphere stroke, although not involving speech directly, is in practice more disabling than a left-hemisphere stroke, despite the fact that in a left-hemisphere stroke speech is usually lost. Following a left-hemisphere stroke, despite the difficulties incurred with loss of speech and loss of use of the right hand, the chances of independent living are higher than after a right-hemisphere stroke.379 It is not just the capacity to interpret emotional signals, in a functional or utilitarian sense, that is mediated by the right hemisphere. While the capacity to interpret other's minds, even to appreciate what they must be thinking and feeling – the capacity that is missing in autism – is lost in a right-hemisphere stroke,380 it is more than that too: it is the capacity positively to empathise. Meaning is more than words.
MUSIC AND TIME
Sometimes it is music. Music, being grounded in the body, communicative of emotion, implicit, is a natural expression of the nature of the right hemisphere. The relationship between language and music is something we will explore in the next chapter: their overlapping functions and origins reveal some vital truths about ourselves. Given that intonation of the voice and the emotional aspects of experience are its special concern, it is to be expected that music would be a largely (though not exclusively) right-hemisphere phenomenon.
There are, however, other respects in which music is a natural candidate for the concerns of the right hemisphere. It is the relations between things, more than entities in isolation, that are of primary importance to the right hemisphere. Music consists entirely of relations, ‘betweenness’. The notes mean nothing in themselves: the tensions between the notes, and between notes and the silence with which they live in reciprocal indebtedness, are everything. Melody, harmony and rhythm each lie in the gaps, and yet the betweenness is only what it is because of the notes themselves. Actually the music is not just in the gaps any more than it is just in the notes: it is in the whole that the notes and the silence make together. Each note becomes transformed by the context in which it lies. What we mean by music is not just any agglomeration of notes, but one in which the whole created is powerful enough to make each note live in a new way, a way that it had never done before. Similarly poetry cannot be just any arrangement of words, but one in which each word is taken up into the new whole and made to live again in a new way, carrying us back to the world of experience, to life: poetry constitutes a ‘speaking silence’. Music and poetic language are both part of the world that is delivered by the right hemisphere, the world characterised by betweenness. Perhaps it is not, after all, so wide of the mark to call the right hemisphere the ‘silent’ hemisphere: its utterances are implicit.
But it is not just because it exists in betweenness that music is the concern of the right hemisphere. Its indivisible nature, the necessity of experiencing the whole at any one time, though it is forever unfolding in time, a thing that is ever changing, never static or fixed, constantly evolving, with the subtle pulse of a living thing (remember, even musical instruments are present to the brain as living things), the fact that its communication is by its nature implicit, profoundly emotive, working through our embodied nature – everything about music, in short, makes it the natural ‘language’ of the right hemisphere. If it is true, as Walter Pater famously said, following Novalis, that all art constantly aspires towards the condition of music, all art aspires to reside in the world that is delivered to us by the right hemisphere.
The relation between music and the body is not by any means confined to voluntary (or apparently voluntary) movements of the limbs, as in dance. We are all aware of the many ways in which music affects us physically through our emotions. Musical phrases act like metaphors emanating from, and enormously expanding the meaning of, movement in and of the body: rising, falling, pulsing, breathing. Many features of music, including obviously syncopations, but also melodic appoggiaturas and enharmonic changes, set up patterns of expectation which are ultimately either confirmed or disappointed;381 and this process leads to physiological reactions such as alterations in breathing, or changes in heart rate, in blood pressure, and even in temperature, as well as bringing us out in a sweat, bringing tears to our eyes, or making our hair stand on end.382 Such changes are again mediated through the right hemisphere's vital connection with subcortical centres, with the hypothalamus, and with the body in general.
It has been said that music, like poetry, is intrinsically sad,383 and a survey of music from many parts of the world would bear that out – not, of course, that there is no joyful music, but that even such music often appears to be joy torn from the teeth of sadness, a sort of holiday of the minor key. It is what we would expect in view of the emotional timbre of the right hemisphere; and there is a stronger affinity between the right hemisphere and the minor key, as well as between the left hemisphere and the major key.384 The pre-Socratic philosopher Gorgias wrote that ‘awe [phrike] and tearful pity and mournful desire enter those who listen to poetry’, and at this time poetry and song were one.385
The relationship between music and emotion is fascinating, and to some degree baffling. Suzanne Langer said that music not only has the power to recall emotions we are familiar with, but to evoke ‘emotions and moods we have not felt, passions we did not know before.’386 Music seems, in other words, to expand the range of possible emotions limitlessly because the emotion experienced is so bound up with the particularity of the work that mediates it, yet the lexicon with which we are obliged to describe the feelings remains frustratingly limited. Thus the ‘sadness’ of a piece of Bach will be quite different from the ‘sadness’ of a piece of Mozart, and ‘sadness’ in the Matthew Passion will be different from the sort of ‘sadness’ we might discern in The Musical Offering, and the ‘sadness’ we experience in one movement of the Matthew Passion – the wonderful alto aria Erbarme dich, for example – will be of a quite different kind from the ‘sadness’ of, say, its final chorus, Wir setzen uns mit Tränen nieder. This must be what Mendelssohn meant by his otherwise paradoxical pronouncement that ‘the thoughts that are expressed to me by music I love are not too indefinite to be put into words, but on the contrary too definite.’387Language returns us inevitably to the worn currency of re-presentation, in which the unique qualities of everything that exists are reduced to the same set of terms. As Nietzsche put it: ‘Compared with music all communication by words is shameless; words dilute and brutalise; words depersonalise; words make the uncommon common.’388
Though speech is principally a left-hemisphere function, the production of words in song is associated with wide activation of the right hemisphere.389 Following a left hemisphere stroke which leaves the patient unable to speak, he or she may be able to sing the words of songs without difficulty. Damage to the right hemisphere, by contrast, can lead to a condition known as amusia, in which the ability to appreciate and understand, or to perform, music may be lost.390 Right-hemisphere lesions may leave the understanding of speech relatively unaffected, while the perception of nonverbal sounds (including music) is profoundly disrupted.391 In such cases, as well as in auditory agnosia (which is commoner following bilateral damage), the perception of timbre, rhythm and complex sounds is badly affected.392 Most cases of amusia without aphasia, inability to appreciate or perform music, but without impairment of speech comprehension or production, involve right-hemisphere damage.393 The reverse situation depends on the right hemisphere being spared. A well-known composer and Professor of Music at Moscow Conservatory, Vissarion Shebalin, had a left temporal and parietal stroke with consequent severe aphasia (impairment of language), but carried on composing works of excellent quality – according to Shostakovich indistinguishable from his pre-stroke works.394 A professional organist and composer who was blind from the age of two had a left middle cerebral artery stroke, with consequent severe aphasia, as well as alexia and agraphia (inability to read or write) in Braille for words – but not for music, and carried on playing and composing unaffected.395 A composer and conductor who had a left-hemisphere stroke was no longer able to read words, but could read and write music without difficulty.396
Melody, tone, timbre and pitch-processing are almost always mediated via the right hemisphere (in non-professional musicians).397 Rhythm is more widely based. Discriminating rhythm patterns activates broadly distributed networks in temporal, inferior parietal and prefrontal cortex almost exclusively in the right hemisphere.398 However, some basic, metrical rhythms are mediated by the left hemisphere, particularly by Broca's area;399 while more complex rhythms, and those with more deviations from the standard pattern, such as syncopations and cross rhythms, are preferentially treated by the right hemisphere.400 The right hemisphere is more sensitive to harmony,401 which could be considered essentially a right-hemisphere function.402 The right hemisphere is also the source of our ability to relate harmony to intonation (the basis for harmonic progression) and to some aspects of rhythm.403
But music raises an intriguing problem. All that I have just said applies to the amateur: the professional or highly trained musician appears to use the left hemisphere to a much greater extent in the understanding of music. This has been interpreted by some as suggesting the adoption of a more consciously learned, theoretically based or analytic approach in such trained subjects. This is almost certainly true. It may also be, as Jerre Levy has argued, that the evidence from both successful artists and musicians suggests that their skills are more widely distributed across both hemispheres than is usual (‘flying mathematicians’ – see p. 12 above).404 This would be in keeping with the finding that visuospatial attention is more evenly distributed between the hemispheres in musicians, possibly because of their having acquired the skill of reading music, a left–right sequential process like language (thus favouring left-hemisphere processing), but the meaning of which is nonetheless represented visuospatially (possibly favouring right-hemisphere processing). Additionally pianists have to be able to use each hand equally to translate between visuospatial and motor sequences.405
The findings of Goldberg and Costa suggest, however, that it may also be a special case of a more generally applicable principle, as we have seen above. While we are gathering new information, the right hemisphere is responsible, but once whatever it is becomes thoroughly ‘known’, familiar, it is taken over by the left hemisphere.406 The discovery that the contrapuntal music of J. S. Bach causes a strong right-hemisphere activation even in trained musicians is fascinating. It was explained by the researchers who made the finding on the basis that a range of melodic contours needs to be maintained in awareness simultaneously, requiring the right hemisphere's greater capacity to hold experience in working memory.407 While that may be right, an alternative explanation might lie in the impossibility of attending to all parts of such music in its entirety, so that it can never be experienced in exactly the same way on different hearings. Because it is never finally captured, it is always new. And the two explanations are perhaps not so different, since the left hemisphere ‘capture’ that results in inauthenticity is possible only by limiting the scope of what is attended to.
Music – like narrative, like the experience of our lives as we live them – unfolds in time. The movement of time is what makes music what it is. Not just that it has ictus and rhythm; its structure extends through and across time, depending on memory to hold it together.
Time is the context that gives meaning to everything in this world, and conversely everything that has meaning for us in this world, everything that has a place in our lives, exists in time. This is not true of abstractions and re-presentations of entities, but all that is is subject to time. The sense of time passing is associated with sustained attention, and even if for that reason alone, it is only to be expected that this arises in the right hemisphere, subserved by the right prefrontal cortex and inferior parietal lobe.408 The ability to compare duration in time is clearly better performed by the right hemisphere,409 and relies on the right dorsolateral prefrontal cortex.410 In fact virtually all aspects of the appreciation of time, in the sense of something lived through, with a past, present and future, are dependent on the right hemisphere, principally the right prefrontal and parietal cortex.411 The sense of past or future is severely impaired in right-hemisphere damage.412
What is called temporal sequencing is an ambiguous concept. Such sequencing, depending on what one means by that, may be right-hemisphere-dependent413 or, at least where the sequence has no ‘real world’ meaning, as it would in a narrative, left-hemisphere-dependent414 – the understanding of narrative is a right-hemisphere skill; the left hemisphere cannot follow a narrative.415 But sequencing, in the sense of the ordering of artificially decontextualised, unrelated, momentary events, or momentary interruptions of temporal flow – the kind of thing that is as well or better performed by the left hemisphere – is not in fact a measure of the sense of time at all. It is precisely what takes over when the sense of time breaks down. Time is essentially an undivided flow: the left hemisphere's tendency to break it up into units and make machines to measure it may succeed in deceiving us that it is a sequence of static points, but such a sequence never approaches the nature of time, however close it gets. This is another instance of how something that does not come into being for the left hemisphere is re-presented by it in non-living, mechanical form, the closest approximation as it sees it, but always remaining on the other side of the gulf that separates the two worlds – like a series of tangents that approaches ever more closely to a circle without ever actually achieving it, a machine that approximates, however well, the human mind yet has no consciousness, a Frankenstein's monster of body parts that never truly lives. A condition called palinopsia, in which there is disturbance and fragmentation of the normal flow of visual experience, or abnormal persistence over time of images, causing visual trails, is caused by posterior right-hemisphere lesions;416 and similar phenomena – loss of fluidity of motion through time – in other modalities than sight are probably similarly associated with deficits in the right posterior cortex.417 Under such conditions the right hemisphere ability to perceive flow as a single, unified motion across time is lost. It becomes replaced, in the left hemisphere's timeless, but mechanical world, by the summing of an infinite series of static moments, rather like the succession of frames in a ciné film, known as the Zeitraffer phenomenon.
Again it has been suggested that, whereas the right hemisphere is required for the sustained ‘monitoring of temporal information’, the left hemisphere is more efficient for detection of brief temporal flow interruptions that are decontextualised.418 In my view this merely confirms the predilection for abstraction, as well as the lack of capacity for perception of temporal flow, in the left hemisphere. The critical point here is that the right hemisphere has an advantage where there is fluency of motion, or flow over time, but the left hemisphere an advantage where there is stasis, or focus on a point in time.419 There is an ambiguity in the idea of permanence. The left hemisphere seems to accept the permanence of something only if it is static. But things can change – flow – and yet have permanence: think of a river. The right hemisphere perceives that there is permanence even where there is flow. Hence, when it is damaged, living beings have no permanency – the Capgras phenomenon.
Music takes place in time. Yet music also has the capacity to make us stand outside time. As George Steiner put it, ‘music is … time made free of temporality’.420 Equally it works through the body, but transports us beyond the world of the merely physical: it is highly particular, and yet seems to speak of things that are universal.421 Perhaps this going ‘through’ a thing to find its opposite is an aspect of the right-hemisphere world, in which ‘opposites’ are not incompatible, an aspect of its roundness, rather than linearity. However, I would say, at the risk of pushing language to or beyond its proper limits, that time itself is (what the left hemisphere would call) paradoxical in nature, and that music does not so much free time from temporality as bring out an aspect that is always present within time, its intersection with a moment which partakes of eternity. Similarly it does not so much use the physical to transcend physicality, or use particularity to transcend the particular, as bring out the spirituality latent in what we conceive as physical existence, and uncover the universality that is, as Goethe spent a lifetime trying to express, always latent in the particular. It is also a feature of music in every known culture that it is used to communicate with the supernatural, with whatever is by definition above, beyond, ‘Other than’, our selves.422
The equivalent of time in the visual realm could be thought of as spatial depth: indeed since Einstein we have come to understand that time and space are aspects of one entity. As it is the right hemisphere that gives ‘depth’ to our sense of time, in the visual realm it is the right hemisphere that gives us the means of appreciating depth in space,423 the way in which we stand in relation to others, rather than by categorisation. The right hemisphere has a tendency to deal with spatial relations in terms of the degree of distance, which it can discriminate easily, in contrast with the strategy of the left hemisphere, which tends to be more categorical: ‘above’, ‘below’, and so on.424 There is a parallel here with the sense of time: duration belongs to the right hemisphere, while sequencing (‘before’, ‘after’ = ‘above’, ‘below’) belongs to the left. The right hemisphere's organisation of space depends more on depth, whether things are nearer or further ‘from me’.425 The right hemisphere is even biased towards what lies further ‘from me’, an aspect of its broader, wider and deeper attention.426 The left hemisphere, by comparison, has difficulty with processing depth: as a result, it may get the size of things wrong, sometimes dramatically.427
Right-hemisphere deficits cause difficulty in dealing with irregular smoothly curved surfaces, such as are characteristic of living things, in three dimensions, even though the capacity to deal with a predictable rectilinear 3D object like a cube is spared. It has been suggested that this problem in dealing with curved volumes may underlie prosopagnosia,428 and it might be a contributing factor. One of the features Bodamer's ‘Patient S’ described was, after all, the lack of depth, the reduction of the face to a ‘white oval plate’.429
The right hemisphere tends to present the world realistically, with visual detail and in three dimensions, with depth; and an aesthetic sense of the intensity and beauty of visual representations comes largely from the right hemisphere.430
The right hemisphere represents objects as having volume and depth in space, as they are experienced; the left hemisphere tends to represent the visual world schematically, abstractly, geometrically, with a lack of realistic detail, and even in one plane (see Figures 2.8 and 2.9).431
Drawings of buildings, in individuals with an inactivated right hemisphere, may even be laid out flat with all façades simultaneously visible, as in a child's drawing.432 One way of putting this is that the left hemisphere is concerned with what it knows, where the right hemisphere is concerned with what it experiences (see Figure 2.10).
A patient studied by Gazzaniga and LeDoux, who underwent a commissurotomy, could draw a cube normally with either hand prior to the operation, but following the procedure could draw only a poor diagram with his favoured right hand, though the left hand was able to draw a 3-dimensional construct of a cube (see Figure 2.11).433
Fig. 2.8 Hemisphere differences and abstraction (Nikolaenko, 1997)
Fig. 2.9 Hemisphere differences and visual depth (Nikolaenko, 1997)
Fig. 2.10 Hemisphere differences: what we see v. what we know (Nikolaenko, 1997)
Fig. 2.11 Cube drawing before and after commissurotomy (Gazzaniga & Le Doux, 1978)
The left hemisphere likes things that are man-made. Things we make are also more certain: we know them inside out, because we put them together. They are not, like living things, constantly changing and moving, beyond our grasp. Because the right hemisphere sees things as they are, they are constantly new for it, so it has nothing like the databank of information about categories that the left hemisphere has. It cannot have the certainty of knowledge that comes from being able to fix things and isolate them. In order to remain true to what is, it does not form abstractions, and categories that are based on abstraction, which are the strengths of denotative language. By contrast, the right hemisphere's interest in language lies in all the things that help to take it beyond the limiting effects of denotation to connotation: it acknowledges the importance of ambiguity. It therefore is virtually silent, relatively shifting and uncertain, where the left hemisphere, by contrast, may be unreasonably, even stubbornly, convinced of its own correctness.434 As John Cutting puts it, despite ‘an astonishing degree of ignorance on the part of the left (supposed major) hemisphere about what its partner, the right (supposed minor) hemisphere, [is] up to, [it] abrogates decision-making to itself in the absence of any rational evidence as to what is going on’.435
There are numerous examples of this phenomenon. A split-brain subject, to whose right hemisphere a photograph of a nude in a suggestive pose is projected, becomes flustered and laughs in an embarrassed fashion. When the experimenter asks her why, her verbal left hemisphere has no idea. She therefore makes something plausible up – someone in the room is upsetting her.
But a famous example, reported by Gazzaniga and LeDoux, illustrates the most important point here. The experimenters show a split-brain patient (PS) a picture projected to one or other hemisphere and askhim to pick a card connected with the scene. For example, they show a snow scene to the right hemisphere and ask him to choose an appropriate picture from an array of cards, with either hand. He cannot say what it is that he has seen, because the right hemisphere cannot speak, but he is able with his left hand to go straight to the picture of a shovel. However, since the left hemisphere did not see anything, his right hand chooses at random, and scores no better than chance. Then they make things a bit more interesting. At the same time that they flash a picture of the snow scene to the right hemisphere, they flash a picture of a chicken claw to the left hemisphere. Each hemisphere has knowledge of only one image, and in each case it is different. When they ask PS to choose an appropriate card, again his left hand chooses a shovel (because the right hemisphere has seen the snow), but the right hand chooses a picture of a chicken (because what the left hemisphere has seen is the chicken claw). When asked why his left hand had chosen the shovel, his verbal left hemisphere, which has to respond to the question, but knows nothing of the snow scene, the real reason for choosing the shovel, is not in the least abashed. He explains that he saw a chicken,' and of course chose the shovel because ‘you need that to clean out the chicken shed’.
The really interesting finding here, as the authors themselves put it, is that ‘without batting an eye’ the left hemisphere draws mistaken conclusions from the information available to it and lays down the law about what only the right hemisphere can know: ‘yet, the left did not offer its suggestion in a guessing vein but rather [as] a statement of fact …’436
This may be linked to a phenomenon known as confabulation, where the brain, not being able to recall something, rather than admit to a gap in its understanding, makes up something plausible, that appears consistent, to fill it. Thus, for example, in the presence of a right-sided lesion, the brain loses the contextual information that would help it make sense of experience; the left hemisphere, nothing loath, makes up a story, and, lacking insight, appears completely convinced by it.437 Even in the absence of amnesia, the left hemisphere exhibits a strong tendency to confabulate: it thinks it knows something, recognises something, which it doesn't, a tendency that may be linked to its lack of ability to discriminate unique cases from the generalised categories into which it places them.438 The left hemisphere is the equivalent of the sort of person who, when asked for directions, prefers to make something up rather than admit to not knowing. This impression is confirmed by Panksepp: ‘The linguistically proficient left hemisphere … appears predisposed to repress negative emotions, and even chooses to confabulate.’439 To some extent perhaps we inevitably confabulate stories about our lives, a process overseen by what Gazzaniga calls the left-hemisphere ‘interpreter’.440 However, it is the right hemisphere that makes judgments about the truth or plausibility of these narratives.441
The fact is that this habit is far from harmless: it leads the left hemisphere to make poor inferences and some mistaken choices. In one experiment by Gazzaniga's colleagues, split-brain subjects (JW & VP) were asked to guess which colour, red or green, was going to be displayed next, in a series where there were obviously (four times) more green than red.442 Instead of spotting that the way to get the highest score is to choose green every time (the right hemisphere's strategy), leading to a score of 80 per cent, the left hemisphere chose green at random, but about four times more often than red, producing a score of little better than chance. The problem here, as subsequent research has illuminated, is that the left hemisphere develops a rule – a rule that is, however, wrong.443
Fig. 2.12 Duck-rabbit (Popular Science Monthly, 1899)
In a similar, earlier experiment in normal subjects, researchers found that, not only does (what we now know to be) the left hemisphere tend to insist on its theory at the expense of getting things wrong, but it will later cheerfully insist that it got it right. In this experiment, the researchers flashed up lights with a similar frequency (4:1) for a considerable period, and the participants again predicted at random in a ratio of 4:1, producing poor results. But after a while, unknown to the subjects, the experimenters changed the system, so that whichever light the subject predicted, that was the light that showed next: in other words, the subject was suddenly bound to get 100 per cent right, because that was the way it was rigged. When asked to comment, the subjects – despite having carried on simply predicting the previously most frequent light 80 per cent of the time – overwhelmingly responded that there was a fixed pattern to the light sequences and that they had finally cracked it. They went on to describe fanciful and elaborate systems that ‘explained’ why they were always right.444
So the left hemisphere needs certainty and needs to be right. The right hemisphere makes it possible to hold several ambiguous possibilities in suspension together without premature closure on one outcome. The right prefrontal cortex is essential for dealing with incomplete information and has a critical role to play in reasoning about incompletely specified situations. The right hemisphere is able to maintain ambiguous mental representations in the face of a tendency to premature over-interpretation by the left hemisphere.445 The right hemisphere's tolerance of uncertainty is implied everywhere in its subtle ability to use metaphor, irony and humour, all of which depend on not prematurely resolving ambiguities. So, of course, does poetry, which relies on right-hemisphere language capacities. During ambiguous stimulation of perceptual rivalry (the phenomenon of an ambiguous figure that can be seen in one way or another, but not both simultaneously, such as the duck–rabbit above or the Necker cube opposite446 ) right frontal cortex is more active.447
Fig. 2.13 Necker cube
Blurred or indistinct images are not a problem for the right hemisphere, but are for the left, even where the nature of the task would suggest that it should be more problematic for the right hemisphere.448 One of the most consistent early findings in hemisphere specialisation was that whenever an image is either only fleetingly presented, or presented in a degraded form, so that only partial information is available, a right-hemisphere superiority emerges – even when the material is verbal.449 In some subtle experimental work Justine Sergent was able to demonstrate this and its converse, namely that when images are presented for longer than usual, thus increasing their certainty and familiarity, a left-hemisphere superiority emerges, even when it comes to face recognition. She makes the interesting observation that letters of the alphabet ‘represent a finite set of stimuli that are sharply focussed, familiar and overlearned’, whereas visual images ‘represent a potentially infinite set of shapes of large visual angle size, with different levels of structure of unequal importance and salience that are most often unfamiliar to subjects’. In doing so she neatly reveals a common thread which unites, on the one hand, the left hemisphere's affinity for what it itself has made (here language), well-worn familiarity, certainty and finitude, and, on the other, the right hemisphere's affinity for all that is ‘other’, new, unknown, uncertain and unbounded.450 Again what have to be referred to, in an account such as I am giving in this chapter, left-hemisphere fashion, as separate ‘functions’ (or areas of concern), should also be seen, right-hemisphere fashion, as aspects of one and the same entity that are only artificially separated in the process of description. The ‘functions’ are not arbitrarily housed together in this or that hemisphere: they form, in the case of either hemisphere, aspects of two whole ways of being in the world.
Certainty is also related to narrowness, as though the more certain we become of something the less we see. To put this in the context of the neurophysiology of vision: the fovea of the human eye, a tiny region in the retina at the centre of gaze, is the most pronounced of that of all primates. Here resolution is about 100 times that at the periphery.451 But it is only about 1° across. The part of the visual field that is actually brought into resolution is no more than about 3° across. This is where the narrow focussed beam of left-hemisphere attention is concentrated: what is clearly seen.
SELF-AWARENESS AND EMOTIONAL TIMBRE
The right hemisphere is also more realistic about how it stands in relation to the world at large, less grandiose, more self-aware, than the left hemisphere.452 The left hemisphere is ever optimistic, but unrealistic about its short-comings. When patients who have had a right-hemisphere stroke are offered constructive guidance about their performance it makes little impact.453 In the words of one researcher into head injury, ‘children with right-brain deficit disorder ignore task obstacles, accept impossible challenges, make grossly inadequate efforts, and are stunned by the poor outcomes. These children act fearless because they overlook the dangers inherent in the situation.’454 A highly intelligent professional described by Stuss was completely unaware of his lack of capacity to do his job after the removal of a tumour in the right prefrontal cortex. When asked to role-play as an occupational health adviser to someone with his problems, he appropriately advised medical retirement, but when asked to apply this insight to his own situation he was completely unable to do so.455 There are many similar case reports.456
Although relatively speaking the right hemisphere takes a more pessimistic view of the self, it is also more realistic about it.457 There is evidence that (a) those who are somewhat depressed are more realistic, including in self-evaluation; and, see above, that (b) depression is (often) a condition of relative hemisphere asymmetry, favouring the right hemisphere.458 Even schizophrenics have more insight into their condition in proportion to the degree that they have depressive symptoms.459 The evidence is that this is not because insight makes you depressed, but because being depressed gives you insight.460
Insight into illness generally is dependent on the right hemisphere, and those who have damage to the right hemisphere tend to deny their illness – the well-recognised, and extraordinary phenomenon of anosognosia, in which patients deny or radically minimise the fact that they have, for example, a blatant loss of use of what may be one entire half of the body.461 A patient with a completely paralysed (left) limb may pointedly refuse to accept that there is anything wrong with it, and will come up with the most preposterous explanations for why he is not actually able to move it on request. This happens to some degree in the majority of cases after a stroke affecting the left side of the body (involving right-hemisphere damage), but practically never after a right-sided stroke (involving left-hemisphere damage). The phenomenon of denial can be temporarily reversed by activating the affected right hemisphere.462 Equally, denial of illness (anosognosia) can be induced by anaesthetising the right hemisphere.463
Note that it is not just a blindness, a failure to see – it's a wilful denial. Hoff and Pötzl describe a patient who demonstrates this beautifully: ‘On examination, when she is shown her left hand in the right visual field, she looks away and says ‘I don't see it.’ She spontaneously hides her left hand under the bedclothes or puts it behind her back. She never looks to the left, even when called from that side.’464 If forced to confront the affected limb, there is not infrequently a sense of revulsion from it, known as misoplegia: if the examiner puts the patient's own left hand in her right hand, ‘she takes hold of it only to drop it immediately with an expression of disgust’.465
In right-hemisphere lesions, there is not only denial or indifference in the face of incapacity, but sometimes a disturbance of mood ‘reminiscent of the fatuousness of those with frontal lesions: euphoria, joviality, a penchant for feeble puns’. One of the patients reported by Hécaen and de Ajuriaguerra, who had complete hemi-asomatognosia caused by a parietal tumour ‘exhibited a surprising joviality, at the same time complaining of a fierce headache.’466
Denial is a left-hemisphere speciality: in states of relative right-hemisphere inactivation, in which there is therefore a bias toward the left hemisphere, subjects tend to evaluate themselves optimistically, view pictures more positively, and are more apt to stick to their existing point of view.467 In the presence of a right-hemisphere stroke, the left hemisphere is ‘crippled by naively optimistic forecasting of outcomes’.468It is always a winner: winning is associated with activation of the left amygdala, losing with right amygdala activation.469
There are links here with the right hemisphere's tendency to melancholy. If there is a tendency for the right hemisphere to be more sorrowful and prone to depression, this can, in my view, be seen as related not only to being more in touch with what's going on, but more in touch with, and concerned for, others. ‘No man is an island’: it is the right hemisphere of the human brain that ensures that we feel part of the main. The more we are aware of and empathically connected to whatever it is that exists apart from ourselves, the more we are likely to suffer. Sadness and empathy are highly correlated: this can be seen in studies of children and adolescents.470 There is also a direct correlation between sadness and empathy, on the one hand, and feelings of guilt, shame and responsibility, on the other.471 Psychopaths, who have no sense of guilt, shame or responsibility, have deficits in the right frontal lobe, particularly the right ventromedial and orbitofrontal cortex.472
Perhaps to feel at all is inevitably to suffer. The Greek word pathe, feeling, is related to pathos, an affliction, and to paschein, to suffer: the same roots are in our word ‘passion’ (and a similar development leads to the German word for passions, Leidenschaften, from the root leiden, to suffer). This is just one reason to doubt the easy equation between pleasure and happiness, on the one hand, and ‘the good’, on the other.
Intrinsically caring for another essentially involves a certain disposition, the disposition to experience sorrow at the other's serious misfortune … To be just is to be disturbed by injustice. Pain, suffering, and the loss of pleasure, then, sometimes constitute who we are and what we value. They are essentially woven into our deepest commitments. As reasons flow from our deepest commitments, we will sometimes have non-instrumental reason to suffer.473
Once, when Berlioz sobbed at a musical performance a sympathetic onlooker remarked: ‘You seem to be greatly affected, monsieur. Had you not better retire for a while?’ In response, Berlioz snapped: ‘Are you under the impression that I am here to enjoy myself?’474
When Lear cries, ‘Is there any cause in nature that makes these hard hearts?’, we could reply, on one level, yes – a defect in the right prefrontal cortex.475 But that just illuminates the fact that cruelty does not exist in ‘nature’: only humans with their left prefrontal cortex have the capacity for deliberate malice. But then only humans, with their right prefrontal cortex, are capable of compassion.
Another area where analytic retrospection misleads us as to the nature of what we are seeing, since it reconstructs the world according to left-hemisphere principles, is that of morality. Moral values are not something that we work out rationally on the principle of utility, or any other principle, for that matter, but are irreducible aspects of the phenomenal world, like colour. I agree with Max Scheler,476 and for that matter with Wittgenstein,477 that moral value is a form of experience irreducible to any other kind, or accountable for on any other terms; and I believe this perception underlies Kant's derivation of God from the existence of moral values, rather than moral values from the existence of a God. Such values are linked to the capacity for empathy, not reasoning; and moral judgments are not deliberative, but unconscious and intuitive, deeply bound up with our emotional sensitivity to others.478 Empathy is intrinsic to morality.
Patients with lesions in the ventromedial frontal lobes are impulsive, fail to foresee consequences and are emotionally disengaged from others; in particular the right ventromedial frontal cortex, which has rich interconnections with limbic structures, is critical to every aspect of moral and social behaviour.479 Moral judgment involves a complex right-hemisphere network, particularly the right ventromedial and orbitofrontal cortex, as well as the amygdala in both hemispheres.480 Damage in the right prefrontal cortex may lead to frank psychopathic behaviour.
Our sense of justice is underwritten by the right hemisphere, particularly by the right dorsolateral prefrontal cortex.481 With inactivation of this area, we act more selfishly. This is probably related to the right frontal lobe's capacity to see the other's point of view, and for empathy in general. I will discuss the relation between altruism and the right hemisphere in Chapter 4. The right frontal lobe's capacity to inhibit our natural impulse to selfishness means that it is also the area on which we most rely for self-control and the power to resist temptation.482
I think we can also make a connection here with a rather fundamental difference between the hemispheres. The left hemisphere's ‘stickiness’, its tendency to recur to what it is familiar with, tends to reinforce whatever it is already doing. There is a reflexivity to the process, as if trapped in a hall of mirrors: it only discovers more of what it already knows, and it only does more of what it already is doing. The right hemisphere by contrast, seeing more of the picture, and taking a broader perspective that characteristically includes both its own and the left hemisphere's, is more reciprocally inclined, and more likely to espouse another point of view. One way of thinking of this is in terms of feedback systems. Most biological systems seek homeostasis: if they move too far in one direction, they stabilise themselves by self-correction. This is ‘negative feedback’, the most familiar example of which is the operation of a thermostat: if the temperature constantly tends to drop, the thermostat triggers a heating system that will act to bring the temperature back to the desired level. However, systems can become unstable and enter a situation in which ‘positive feedback’ obtains – in other words, a move in one direction, rather than producing a move in the opposite direction, serves to promote further moves in the same direction, and a snowballing effect occurs. The right hemisphere, then, is capable of freeing us through negative feedback. The left hemisphere tends to positive feedback, and we can become stuck.483 This is not unlike the difference between the normal drinker and the addict. After a certain point, the normal drinker begins to feel less like another drink. What makes an addict is the lack of an ‘off switch’ – another drink only makes the next, and the next, more likely. And, interestingly enough, lesions of the frontolimbic systems, mainly in the right hemisphere, are associated with addictive behaviour. Pathological gamblers, for example, have frontal deficits which are mainly right-sided;484 by contrast, in cocaine addicts, for example, stimulating the right prefrontal cortex reduces craving for cocaine.485 And denial, a left-hemisphere speciality, is typical of addiction.
Conscious awareness of the self is a surprisingly late development in evolution. The higher apes, such as chimpanzees and orang-utans, are capable of self-recognition, but monkeys are not: they fail the mirror test.486 The right prefrontal region is critically involved in self-recognition, whether by face or by voice.487 Imaging studies of self-recognition by face or voice confirm the importance of the right frontal region and the right cingulate cortex.488 An important correlate of self-awareness in humans is the correct use of the personal pronouns ‘I’ and ‘me’, which is lacking in autism, a condition which replicates many right-hemisphere deficits.489
Clearly no one hemisphere can on its own constitute the self. The self is a complex concept, but, in brief, the self as intrinsically, empathically inseparable from the world in which it stands in relation to others, and the continuous sense of self, are more dependent on the right hemisphere, whereas the objectified self, and the self as an expression of will, is generally more dependent on the left hemisphere. Some studies in split-brain subjects suggest a right-hemisphere advantage for self-recognition;490 but others reveal that both hemispheres equally can recognise the self objectively, though the right hemisphere has an advantage for recognising familiar others.491
The personal ‘interior’ sense of the self with a history, and a personal and emotional memory, as well as what is, rather confusingly, sometimes called ‘the self-concept’, appears to be dependent to a very large extent on the right hemisphere. The self-concept is impaired by right-hemisphere injury, wherever in the right hemisphere it may occur;492 but the right frontal region is of critical importance here.493 This could be described as self-experience. The right hemisphere seems more engaged by emotional, autobiographical memories.494 It is hardly surprising that the ‘sense of self’ should be grounded in the right hemisphere, because the self originates in the interaction with ‘the Other’, not as an entity in atomistic isolation: ‘The sense of self emerges from the activity of the brain in interaction with other selves.’495 The right orbitofrontal cortex, the part of the right frontal lobe most crucial for social and empathic understanding, is larger in primates than the left.496 It is likely that this part of the brain expands during the period of playful interaction between infant and mother in the second half of the first year, and the second year, of life, during which the sense of the self emerges, and indeed the right orbitofrontal cortex is seen by Allan Schore as the crucible of the growing self.497 The right hemisphere matures earlier than the left, and is more involved than the left in almost every aspect of the development of mental functioning in early childhood, and of the self as a social, empathic being.498 Social development in the infant takes place independently of language development, another pointer to its right-hemisphere origins.499
The relationship between the evolution of a sense of self and the sense of others as beings like oneself, and therefore as evoking empathy and understanding, which I have referred to before as an achievement of the right frontal lobes, is borne out by the close relationship between the development of a sense of self and the development of ‘theory of mind’ (see p. 57 above). This is, for example, evidenced by the fact that the neuroimaging correlates of both self-awareness and theory of mind lie in the right frontal and right cingulate cortex.500
It is also the right hemisphere which is responsible for ‘maintaining a coherent, continuous and unified sense of self’.501 Evidence from patients with dementia is highly suggestive that it is the right hemisphere that ‘connects the individual to emotionally salient experiences and memories underlying self-schemas’, and which therefore forms ‘the glue holding together the sense of self’.502 The remark is reminiscent of a formulation of Douglas Watt's that ‘emotion binds together virtually every type of information the brain can encode … [it is] part of the glue that holds the whole system together,’503 and indeed, to the degree that that is true, the observation that the right hemisphere binds together the sense of self would follow from this. And as already implied in the brief discussion of the hemispheres and time, it is the right (prefrontal) cortex, in conjunction with its reciprocal connections with other cortical and subcortical structures, which enables human adults to see themselves as just that – selves, with continuous existence over time.504Right frontal damage impairs the sense of self over time – self with a narrative, and a continuous flow-like existence.505
Sperry and his colleagues hypothesised that it is a right-hemisphere network that gives rise to self-awareness.506 The right hemisphere is preferentially involved in ‘the processing of self-images, at least when self-images are not consciously perceived’.507 In particular, a right frontoparietal network in the human brain seems critical for distinguishing the self from others.508 Activation in the right inferior and medial parietal region, namely the anterior precuneus and posterior cingulate cortex, is proportionate to the degree that stimuli are perceived as referring to the self.509 When subjects look at an image of their own face, activation is seen in the right hemisphere, especially at the right occipitotemporoparietal junction and in the right frontal operculum.510
Individuals may neglect or misidentify their own hands and feet when the right hemisphere – but not when the left hemisphere – is damaged or temporarily inactivated.511 Asomatognosia, the condition in which subjects fail to recognise their embodied self or parts of their own body, is found in nearly 90 per cent of subjects following any right-hemisphere stroke;512 and, conversely, the condition appears to be associated only with right-hemisphere deficits – Feinberg, who has made a study of the condition, notes that of the 100 cases known to him, not once has it followed left-hemisphere damage.513
In keeping with this, those with damage to the right frontotemporal cortex may experience a cognitive detachment from self.514 When subjects read a first-person narrative, they activate the precuneus and anterior cingulate cortex bilaterally, but also preferentially the right temporo-parietal junction, compared with reading a third-person narrative.515
Philosophers spend a good deal of time inspecting and analysing processes that are usually – and perhaps must remain – implicit, unconscious, intuitive; in other words, examining the life of the right hemisphere from the standpoint of the left. It is perhaps then not surprising that the glue begins to disintegrate, and there is a nasty cracking noise as the otherwise normally robust sense of the self comes apart, possibly revealing more about the merits (or otherwise) of the process, than the self under scrutiny. Schizophrenics, like philosophers, have a problem with the sense of the self which ordinary individuals, involved with living, lack. As Wittgenstein once remarked: ‘it's strange that in ordinary life we are not troubled by the feeling that the phenomenon is slipping away from us, the constant flux of appearance, but only when we philosophise. This indicates that what is in question here is an idea suggested by a misapplication of our language.’516 Could this be read as the ‘misapplication of language’ – in other words, the faulty procedure of seeking truth by standing in the world of the left hemisphere while looking at the world of the right?
One recent elegant experiment underlines the key role played by the right hemisphere in the recognition of the self, and at the same time emphasises the left hemisphere's affinity with public, rather than personal, knowledge. Using the Wada test, each subject was shown a computer-generated picture of the subject's own face morphed with that of a person famous in public life. After the anaesthetic wore off, the subjects were then shown the separate pictures of the famous person and of themselves, and were asked which more closely resembled the picture they had previously seen. Those who had viewed the picture with their right hemisphere chose the picture of themselves: those who had viewed it with their left hemisphere chose the picture of the famous person.517 In this study nine out of ten cases conformed to this pattern. Although there is one commissurotomy (‘split-brain’) case reported that appears to suggest the opposite,518 virtually all other evidence points to the key role of the right hemisphere in self-recognition.519
The right frontal region appears to be essential for the determination of self in other modalities, too, such as voice recognition.520 Damage to the right parietal and medial regions may result in confusions of self with other;521 damage to the right frontal lobe creates a disturbance of ego boundaries, suggesting ‘that the right hemisphere, particularly the right frontal region, under normal circumstances plays a crucial role in establishing the appropriate relationship between the self and the world’.522 It is this region that is so obviously not functioning properly in schizophrenia, where subjects not only lack empathy, humour, metaphorical understanding, pragmatics, social skills and theory of mind, but crucially mistake the boundaries of self and other, even at times feeling themselves to melt into other individuals or that other beings are invading or occupying their own body space.
Important aspects of self-awareness in the sense of how we are likely to seem or come across to others – akin to insight – also depend on the right hemisphere. The capacity to understand one's self as a human being like others, which is involved in self-awareness, is an aspect of the human ability to identify with others, empathise with them and share their feelings, dependent as we have seen, on the right hemisphere. The right inferior parietal lobule plays a crucial role both in planning523 and monitoring the outcomes524 of one's own actions.
It was one of the earliest perceptions that the left hemisphere is the seat of conscious self-awareness, certainly for the expression of its selfhood through the conscious will.525 I have already suggested that the expression of the will, in the sense of the conscious, rational will – grasping and manipulating – may have been responsible for the expansion of the left hemisphere. Nonetheless it turns out that when we are acting ‘for ourselves’, in the sense of initiating new action rather than following another's lead, the activity is largely in the right hemisphere, though this may be restricted to practical, habitual actions.526 There is a tendency for independence and motivation to be associated with the right hemisphere, and passivity with the left hemisphere. This is related to its stickiness, described above, its relative inability to shift set, espouse a new way of looking at things, rather than get locked into environmental cues. ‘Environmental dependency’ syndrome refers to an inability to inhibit automatic responses to environmental cues: it is also known as ‘forced utilisation behaviour’. Individuals displaying such behaviour will, for example, pick up a pair of glasses that are not their own and put them on, just because they are lying on the table, involuntarily pick up a pen and paper and start writing, or passively copy the behaviour of the examiner without being asked to, even picking up a stethoscope and pretending to use it. According to Kenneth Heilman, the syndrome, as well as aboulia (loss of will), akinesia (failure to move), and impersistence (inability to carry through an action) are all commoner after right, rather than left, frontal damage.527 In four out of the five cases of environmental dependency in Lhermitte's classic paper in which the syndrome was first described, the only or principal lesion was in the right frontal lobe. In each case the patient explained that ‘you held out objects to me; I thought I had to use them’.528 However, the situation is far from straightforward, since my reading of further data provided by Lhermitte is that the syndrome is as common after lesions in either frontal lobe;529 and a lesion in either frontal lobe may, in any case, ‘release’ behavioural patterns characteristic of the posterior hemisphere on the same side (see below), as much as impair the functioning of the hemisphere as a whole (or indeed the contralateral hemisphere via the corpus callosum). But it would be in keeping with other research that shows forced utilisation behaviour after right-hemisphere damage: one patient not only showed exaggerated responses to external cues (utilization behaviour), and motor impersistence, but a right-handed instinctive grasp reaction, after an infarct in the right thalamus, which was associated with under-perfusion of the entire right cerebral cortex, especially the frontal area.530
In reality we are a composite of the two hemispheres, and despite the interesting results of experiments designed artificially to separate their functioning, they work together most of the time at the everyday level. But that does not at all exclude that they may have radically different agendas, and over long time periods and large numbers of individuals it becomes apparent that they each instantiate a way of being in the world that is at conflict with the other.
CODA: THE ‘FRONT–BACK’ PROBLEM
I mentioned at the beginning of this chapter that there was one intrahemispheric rather than interhemispheric regional difference that I needed to refer to. This involves the relationship of the frontal lobes, the most highly evolved and most distinctively human of all regions of the brain, with the processes going on elsewhere in the brain, including the posterior cortex, which they exist to exert control over. The frontal lobes achieve what they achieve largely through what is normally described as inhibition of the posterior part of the same hemisphere. It might be better described, however, especially in the case of the right hemisphere, as modulation – the inhibitory effect is ‘significantly more pronounced’ in the case of the left hemisphere, perhaps in keeping with its less integrated, more black and white, style.531 This relationship between ‘front’ and ‘back’ is another example of paired ‘opponent processors’ enabling fine modulation of response (see p. 9 above).
What do I mean by modulation? A process that resists, but does not negate. It is best thought of as the imposition of necessary distance, or delay, enabling something new to come forward. In this way it is like the apparently antagonistic relationship of the two hemispheres (a topic which I will explore at length later in the book): it is neither that the products of one hemisphere negate the products of the other, nor that in some bland sense they merely ‘complement’ one another. Their incompatibility permits instead, in a dialectical synthesis, something new to arise. To take an example: if the right hemisphere's immediacy of association with emotion and the body leads it to prioritise what is close, what is ‘mine’, the right frontal lobe brings distance and delay to espousing ‘my’ position. As a result it enables others to stand forth as individuals like ‘me’; it enables a broader empathy and the beginnings of altruism. This is not a negation of something by the frontal lobe, but a modulation of it, an ‘unpacking’, if you like, of something that was there all along, albeit in germ only – something that comes to life only when a degree of necessary distance is interposed. Or to take another example, this time from the left hemisphere. The relative detachment from the body displayed by the left hemisphere, and its tendency to abstraction, normally serve its purposeful striving towards individual gain. The left frontal lobe, however, brings distance, and allows the experience of the peaceful detachment from the material realm and ‘emptying out’ described by experts in meditation as a mystical experience. Again this is no negation, but an elaboration, of what the left hemisphere affords. There is not likely to be ‘a God spot’ in the brain, and the area is fraught with problems of terminology and methodology: but there are areas that are often implicated as accompaniments of religious experience.532 An appropriately cautious and objective review of the literature to date by Michael Trimble concludes that there is a slow accumulation of evidence in favour of religious experience being more closely linked with the ‘non-dominant’ hemisphere, especially the posterior right hemisphere (temporoparietal region). But, to illustrate my point, the other region that is implicated lies in the left frontal lobe – specifically because of its power to inhibit the posterior left hemisphere (temporoparietal region), the seat of language and of sequential analysis.533
The literature on brain function is enormously extensive, and increasing geometrically with every passing day. This chapter cannot, in the nature of things, pretend to be an exhaustive review: to achieve that alone would require a team of experts, and a book several times the size of this one. Rather it is designed to highlight the differences between the hemispheres, where there is coherent evidence, and particularly to reverse the entrenched prejudice that, while the right hemisphere may add a bit of colour to life, it is the left hemisphere that does the serious business. With the (admittedly hugely important) exception of explicit manipulation involving language and serial analysis, the left hemisphere is not the ‘dominant’ hemisphere. Language and analysis will form the subject of the next chapter. What I have tried here to convey is the sheer extent, and something of the feel, of our dependence on the right hemisphere, all of which stands in complete contrast to the view of it as the ‘silent’ hemisphere. This, and the still current soubriquet, the ‘minor’ hemisphere, should make us think about the way in which we view ourselves. We are so used to focussing on utility and ‘function’ that the fact that right-hemisphere damage may completely alter the way in which we stand in relation to the world, and fundamentally change our mode of being, has gone until recently virtually unnoticed. Indeed at the risk of appearing to allow the left hemisphere even less to walk away with, I should point out that there is evidence that even those of the highest verbal, as well as spatial, ability probably rely to a greater extent on the right hemisphere.534 Perhaps inevitably following from that, it turns out that those of highest intelligence, whatever their discipline, may do so.535
Ultimately if the left hemisphere is the hemisphere of ‘what’, the right hemisphere, with its preoccupation with context, the relational aspects of experience, emotion and the nuances of expression, could be said to be the hemisphere of ‘how’. This perhaps explains why conventional neuroscience, being itself largely a manifestation of left-hemisphere activity, has focussed so much on what the brain is doing in which hemisphere, not in what way it does it in each hemisphere, thus, in my view, missing the significance of what it is trying to understand.
Before embarking on this chapter, I suggested that there were two ways of being in the world, both of which were essential. One was to allow things to be present to us in all their embodied particularity, with all their changeability and impermanence, and their interconnectedness, as part of a whole which is forever in flux. In this world we, too, feel connected to what we experience, part of that whole, not confined in subjective isolation from a world that is viewed as objective. The other was to step outside the flow of experience and ‘experience’ our experience in a special way: to re-present the world in a form that is less truthful, but apparently clearer, and therefore cast in a form which is more useful for manipulation of the world and one another. This world is explicit, abstracted, compartmentalised, fragmented, static (though its ‘bits’ can be re-set in motion, like a machine), essentially lifeless. From this world we feel detached, but in relation to it we are powerful.
I believe the essential difference between the right hemisphere and the left hemisphere is that the right hemisphere pays attention to the Other, whatever it is that exists apart from ourselves, with which it sees itself in profound relation. It is deeply attracted to, and given life by, the relationship, the betweenness, that exists with this Other. By contrast, the left hemisphere pays attention to the virtual world that it has created, which is self-consistent, but self-contained, ultimately disconnected from the Other, making it powerful, but ultimately only able to operate on, and to know, itself.
However, as I also emphasised at the outset, both hemispheres take part in virtually all ‘functions’ to some extent, and in reality both are always engaged. I do not wish to leave the impression that it might be a good thing if the entire population had a left-hemisphere stroke. I take it for granted that the contributions made by the left hemisphere, to language and systematic thought in particular, are invaluable. Our talent for division, for seeing the parts, is of staggering importance – second only to our capacity to transcend it, in order to see the whole. These gifts of the left hemisphere have helped us achieve nothing less than civilisation itself, with all that that means. Even if we could abandon them, which of course we can't, we would be fools to do so, and would come off infinitely the poorer. There are siren voices that call us to do exactly that, certainly to abandon clarity and precision (which, in any case, importantly depend on both hemispheres), and I want to emphasise that I am passionately opposed to them. We need the ability to make fine discriminations, and to use reason appropriately. But these contributions need to be made in the service of something else, that only the right hemisphere can bring. Alone they are destructive. And right now they may be bringing us close to forfeiting the civilisation they helped to create.