The Secret Life of the Grown-up Brain: The Surprising Talents of the Middle-Aged Mind - Barbara Strauch (2010)
Part II. The Inner Workings
Chapter 7. Two Brains Are Better Than One
Especially Inside One Head
Of all the unique abilities of the middle-aged brain, perhaps none is as strange—or potentially promising—as its talent for bilateralization.
Bilateralization? Hardly a word to capture the imagination. In fact, as I was looking into this bizarre phenomenon, I kept a file labeled, a bit more enticingly, “Two Brains.”
Still, that’s silly, not to mention inaccurate. But there is something odd taking place and it involves another trick the brain learns, perhaps—though this isn’t completely clear—out of a sense of panic. Sometime in middle age we begin to develop the ability, when faced with a perplexing problem, to use both sides of our brain instead of one. It’s much like using two arms instead of one to pick up a heavy chair, which is not only a better way to lift a chair but may also be a more efficient way to use a brain—and part of the reason we begin to see the big—connected—picture.
Indeed, this two-fisted flair is yet more evidence of how distinctive the middle-aged brain actually is. While it is a characteristic seen later in life, too, this bilateral talent often starts in middle age and may be one of the adaptive strategies some brains adopt to stay strong. “What’s really, really amazing, if I had to name a single thing,” said one scientist speaking about the brain at midlife, “is bilateralization.”
Admittedly, this, too, is not completely good news. Using two arms or two brain parts to accomplish what one arm or one brain part could pull off when younger signals a lack of something somewhere, compensation for a weakness or an absence, you might think.
But an intriguing aspect of this two-brain phenomenon is that it’s not the weakest brains that do this but the most robust ones. A series of recent studies has found that it is the most capable who resort to this trick. It’s as if the best and the brightest older brains, accustomed to being held in the highest esteem, simply refuse to give in. Without breaking a sweat, the old pro steps up to the plate and swings for the fences.
“It’s nice to find out that the brain does this positive thing. It’s not all passive acceptance,” says Roberto Cabeza, a neuroscientist at Duke University who helped to uncover this neuro trick. “Instead, we use what we have left better. It is really encouraging. And it might have the greatest impact at middle age because we’re not retired, we’re still working. We may need it the most.”
It’s also not what scientists expected to find when they finally got tools, such as MRIs, to peer directly inside working brains. They thought they’d find the opposite. For many years it was widely believed that as the brain aged, it used much less of itself, not more. Indeed, the working model of the aging brain was something akin to brain damage. As the brain got older, most believed it became lazier. Earlier cruder measures routinely found that most brains stopped trying as hard, firing up fewer neurons. Older brains were feeble brains.
But that view has now been turned inside out, too.
Old Brain Models Disappear
“Underactivation fit well with a brain-damage model of aging,” explains Patricia Reuter-Lorenz, a neuroscientist at the University of Michigan, who recently wrote a summary of this new view in the journal Current Opinion in Neurobiology. “The largely unanticipated result from functional neuro-imaging is overactivation or greater brain activity in older . . . adults.”
Cheryl Grady, the neuroscientist at the University of Toronto, was one of the first scientists to get a peek at this. In the early 1990s, when Grady was at the National Institutes of Health, she became intrigued by the idea of watching the aging brain with the first real machine that could—a positron emission tomography (PET) scan. A PET scan measures changes in blood flow as brain regions activate, and Grady wanted to find out if an older brain acted in the same way as a younger brain in routine tasks such as matching faces. She began with a set of well-accepted assumptions: Older people would be much worse at this than younger people, and they’d muster fewer brain cells for the task.
Instead, she found neither premise to be true. To her surprise, the older adults performed just as well as the younger ones, and they consistently used more of their brains, not less. They tapped into the same brain circuits as the younger adults, pathways known to be active with face matching. But they also recruited an additional region—their powerful frontal cortex. This was not a matter of brains being distracted and falling into their unhelpful default daydreaming modes. Rather, the most functional brains grabbed their most powerful tool—getting the additional boost they needed from their frontal lobes.
“This was a surprise. We just wanted to see if the older people used the same pathways as the younger ones when they matched faces,” said Grady when I spoke with her not long ago. “We expected that they would do worse on the task and the working model was that the older people would have less activity in their brains. And we certainly did not expect to see more frontal activity. We thought, what the heck does this mean? It was amazing and the whole field has been chasing it since.”
Grady herself has led much of the chase. Just a few years later, in 1997, Grady, along with Robert Cabeza, wanted to determine whether this was simply a fluke. Was it just something that older brains did with relatively simple jobs or would it show up when tackling harder problems that, at any age require help from the elite frontal lobes. To find out, the researchers scanned the brains of young and old adults as they tried not only to learn pairs of words—parents and piano—but also to recall the correct match later on, a complex job in the brain.
And there it was again. Younger brains, as expected, used only the left side of their frontal lobes to first learn the words—called encoding—and switched to the right side of their frontal lobes to retrieve that memory, a pattern that had been well established. They use only one side of their brain at a time for this complex task.
But older adults didn’t fit the pattern at all. They used their brains in a new way. They not only engaged less of their frontal lobes’ left side to form the word memory initially, but they then proceeded to use bothsides, right and left, to do the harder job of recalling the words.
This was a classic case of what many began to call bilateralization, two sides doing the work once done by one. And scientists began to find that it not only occurred in brains as they aged, but that it was the higher-functioning brains that did it. Faced with a challenge, they tapped into whatever they had, to do what they needed to do.
This flies in the face of the idea that it’s better for an older brain to act exactly as it had when younger. Maybe that’s not always the case. “Performance is better if the brain uses two sides,” says Cabeza. “As the [older] brain reorganizes its function, it adds neural possibilities.”
Older brains use more brainpower, more neural juice, to get the job done. And that often begins in middle age. But why? The best explanation is that brains learn to do this as they age because it works. After all, older brains are not recruiting areas willy-nilly. Rather, they call primarily on the part of the brain that helps the most, the frontal lobes, the region that can, as Grady says, “help you perform.”
In all likelihood, this does not come without a downside. If so much brain real estate is being devoted to one thing we’re trying to do, we can expect to come up a little shy when we try to do something else at the same time. Multitasking taxes the brain at any age (think teenagers texting while driving), but we often get progressively worse at it as we age.
“Overactivation . . . might have a hidden cost. To the extent that older brains engage more neural circuitry . . . [they] are more likely to reach a limit on the resources that can be brought to bear,” Reuter-Lorenz has warned.
Better Brains Learn the Trick
But if, as the latest studies indicate, it’s only the savviest brains that learn this trick and do it in the savviest manner—it seems a sign of calculation, not capitulation.
In one 2002 study by Cabeza, for instance, this two-brain phenomenon was distinctly linked to higher abilities overall. A group of older adults was divided by high and low abilities—all within the normal range of cognitive skills. Then they, along with a group of healthy younger adults, were given relatively complex tasks, in this case—again—word-pair matching. As expected, the younger adults, scanned by PET, used the right sides of their brains and did fine on tests of mental skills. The older adults who used only their brains’ right sides, however, were also those who had scored on the low end of cognitive ability. They used the same brain area as those who were younger but used it less efficiently.
But the older adults who used both sides of their frontal lobes were the cognitive champions. Indeed, the pattern was so recognizable that Cabeza, in the 2002 study “Aging Gracefully: Compensatory Brain Activity in High-Performing Older Adults,” gave the pattern a name—HAROLD, for Hemispheric Asymmetry Reduction in Older Adults. Translated, that means that if we’re smart, we figure out how to recruit as much brainpower as we need.
Over the last several years, this idea has been pushed even further, with added twists. Cheryl Grady and psychologist Mellanie Springer at the University of Toronto, for instance, recently found that younger adults used mostly their lower-level temporal lobes to solve a certain memory problem, but older people who performed well instead used their higher-level frontal lobes. And even more interesting, it was those adults with the most education who tapped into this premier brain region.
Is it possible that those with more education had, through the years, simply grown accustomed to drumming up high-level brain reinforcements when necessary? Maybe so. As Grady herself concludes: “The higher the education, the more likely the older adult is to recruit frontal regions, resulting in better memory performance.” Higher education seems to enable older adults to “call up the reserves.”
This suggests that those of us who learn to call up more of our brains are better off in the long run and that this brain trick, as Grady says, has “some functional significance. Older adults who are better able to recruit more areas are the high performers,” she says. “It means in some cases, as we age, it is not just a matter of the brain turning down but the brain turning up.”
It may be, too, that we don’t bother to use two brain sides or recruit higher brain areas when we’re young because with a relatively new brain, it’s just not necessary. With an increase in “neural noise”—that interference from irrelevant information—however, the brain turns to its most powerful region to help it focus.
“It’s like shouting in a quiet place, which doesn’t make any sense and is not an efficient way to communicate,” explains Cabeza of Duke. “But in a noisy place, shouting can work better and is a more effective means of communication.”
Building a Brain Scaffold
Recently, Patricia Reuter-Lorenz and Denise Park of the Center for Brain Health at the University of Texas at Dallas have rolled all these insights into one tidy concept called “scaffolding,” which makes the case that brains are set up on purpose to constantly reorganize and recruit more brain tissue as needed. Our brains are built to roll with the punches, and better—or more carefully cared-for—brains roll best.
“What we think is happening,” Park told me, “is that the brain is continually building new scaffolding, responding to the changes and tiny insults by attempting to rewire and reorganize itself.”
And, Park said, “I suspect that middle age is a kind of crossroads for all this, when the brain either learns or does not learn these new patterns.
“If we maintain good brain health, we build better scaffolding and our capacity to adapt continues. That means that if you make good or bad decisions or good or bad events occur, then that will have consequences. It’s just like if you wear out your joints in your thirties, it might not bother you until you are seventy. It’s the same with the brain. In middle age, it matters what you do.”
Or as Patricia Reuter-Lorenz sums up, quite encouragingly: There’s recently been a “shift from the dismal characterization of aging as an inevitable process of brain damage and decline. Instead, the emerging story . . . is that aging can be successful, associated with gains and losses. It is not necessarily a unidirectional process but rather a complex phenomenon characterized by reorganization, optimization, and enduring functional plasticity that can enable the maintenance of a productive and happy life.”
Indeed, there are those who go even further and suggest that this bilateral use of brainpower may be the key ingredient in the power and creativity of our middle-aged brains. It’s been shown, for instance, that some bilingual older adults, having developed the ability to flexibly negotiate two languages in separate parts of their brains throughout their lives, have smaller age-related declines in brain function. That suggests that those who establish such patterns of using more of their brains early on may be in better shape along the way in a range of different ways.
Gene Cohen, a longtime researcher of aging and author of The Mature Mind, who has studied the connection between art and neurons, thinks creative thoughts and solutions can also be partly traced to this ingenious brain trick. As we age, the two sides of our brains become more intertwined, letting us see bigger patterns, have bigger thoughts—reaching, he believes, the level of art.
“The brains’ left and right hemispheres become better integrated during middle age, making way for greater creativity. . . . The neurons themselves may lose some processing speed with age, but they become ever more richly intertwined . . . that’s why age is such an advantage in fields like editing, law, medicine and coaching and management,” Cohen has written.
“As our brains become more densely wired, they also become less rigidly bifurcated. In most people the left hemisphere specializes in speech, language and logical reasoning while the right hemisphere handles more intuitive tasks such as face recognition and reading emotional cues . . . but this pattern changes as we age. . . . Older [people] tend to use both hemispheres. . . . This neural integration makes it easier to reconcile our thoughts with our feelings.”
Robert Cabeza does not think this idea is crazy at all.
“Maybe that means that if you are doing a task cross-hemisphere you will simply do better,” Cabeza suggests. “We see it with physical things . . . moving a chair with two hands or bending your knees to pick something up. That may be a better way to do things altogether; it prevents injury and it’s better for the whole body. If wisdom is learning to use the brain in different ways, well, maybe, in the end, that works better, too.”
The Genetic Road Map
In the backroom of a lab at Harvard Medical School sits a large box freezer whose contents are kept at 140 degrees below 0. If you lift up the lid, you see rows of small plastic containers, each filled with tiny bits of human brains. The brain samples, carefully coded and cataloged, are from adults ranging in age from 26 to 103.
And it’s in those brains, deep in their microscopic folds, that scientists have found even more evidence that brains embark on different journeys in earnest at midlife. And while those divergent paths may relate to levels of education and other adaptive strategies, the brain’s course is also determined by our genes as well.
We are born with a genetic road map, with certain genes—or segments of the DNA in our cells—programmed to activate certain proteins that, in turn, regulate how our bodies and brains function. But those genes—that DNA—can be damaged along the way, perhaps through a preordained process of normal aging, by the environment we live in, such as the level of toxins we are exposed to, and by how we behave in that environment—whether we exercise, eat right, hit our heads, or get a disease. When damage occurs, genes might not be able to properly tell the proteins in our brain cells what to do.
The scientists tending the frozen brain cells wanted to see if they could find a pattern of gene activity in brains at various ages. And they did. After scanning brain samples with a gene chip, a newly invented tool that can measure gene damage and activity, Harvard researchers found that in terms of overall condition, brains of those under forty and past seventy-three years of age look pretty much as you’d expect: little damage and lots of activity in the first group, and more damage and less action in the other.
But the middle-aged brains were all over the map. The brain of one forty-five-year-old man most resembled that of an average brain of a person over seventy. And the brain of a fifty-three-year-old woman matched those of people in their thirties.
“Individuals may diverge in their rates of aging as they transit through middle age, approaching the state of ‘old age’ at different rates,” said Bruce Yankner, the Harvard neuroscientist who examined the brains in the freezer. Though the brain samples were obtained from cadavers or those undergoing brain surgery, and those conditions could have had some impact, overall the brains were considered normal and indicative of what would be found in healthy, living adults.
“At middle age,” Yankner said, “brains become particularly variable.”
The study by Yankner and his colleagues, published in 2004 in the scientific journal Nature, was the first to take a systematic look at how a brain ages on its most basic level, its genes, using these gene chips or microarrays.
Yankner’s studies, more than any others, have taken advantage of this new technology to try to figure out what is happening at a genetic level as the brain ages. His team has now looked at twenty thousand protein-linked genes in the brain and they’ve found the very same thing twice.
The changes in genes that are affected by aging (about 4 percent of the total) generally begin in our late thirties, much earlier than expected. In particular, Yankner found age-related changes in about twenty genes that are crucial for learning and memory and brain-cell flexibility.
But there’s good news here, too. Yankner found that around the same time—late thirties to early forties—another group of nurse genes steps in to help out. These are the genes that protect and repair neurons from damage, and they begin to work overtime, perhaps delaying the net impact of the damage. This, too, could be part of the reason why cognitive decline often doesn’t show up until later in life—and why some retain their intellectual prowess longer than others. Perhaps some people simply have more nurse genes—or for some reason have been able to retain better-functioning nurse genes—than others. And these microscopic differences begin to show up in middle age.
“There seems to be a similar profile for the young before age 40 and a similar profile after age 73. But the most variable group was between ages 40 and 70. Right around middle age you can see the transition in age-related genes. They were just not aging at the same rate. Some resembled the young and some were more like the old. It was very striking.
“The research is still in early stages, but these changes in genes for synaptic function, learning, and memory could help explain the subtle declines in middle age in abilities such as short-term recall,” Yankner told me when I spoke with him recently.
But, he added, more optimistically, other genes are stepping up to the plate. “These are the ones that protect the cell from damage, help build new connections. So at the same time that there is this decline, there is this compensatory activity kicking in, too. I would guess that with most at middle age, there’s probably a balance between the two.”
Of course which side wins that balance game is obviously crucial. Yankner likes to talk of one ninety-three-year-old woman who was in nearly perfect cognitive shape when she died and donated her brain to Yankner’s lab. And perhaps not surprisingly, when the researchers took a look at her brain, they found she had the genetic brain patterns of a middle-aged person.
“We know that she was cognitively intact and her brain was, too,” Yankner told me.
How can some get so lucky? Is it something they ate or read or did? And how can some, on the other end of the spectrum, get so unlucky, brain-wise? Are the lucky ones better from the get-go, or, as Yankner suspects, do they have—or develop—better repair mechanisms and adaptive strategies in their brains? And do these mechanisms mean that they remain able to call on more of their brains—two brains—to help them out?
It’s possible that all this is simply following some set genetic program. Perhaps along the way, Yankner speculates, evolution produced choices. It may have proven over time that it was more important to keep our heart muscles going strong and let our brains, in particular short-term memory, slip a bit. After all, it might be more important to get our hearts pumping to get away from an angry tiger than to recall exactly what we ate for breakfast.
Still, he, along with most, believes it’s likely that in the end we will find that changes in the aging brain arise not just from genes alone but from a combination of our DNA and the soup it lives in—our environment and the way we live our lives. And that means we can make a real difference—and what we do for ourselves during middle age may be particularly crucial.
“There are a lot of redundant systems built into human cells to repair damage. There is a good system to keep the brain intact,” said Yankner, who at age fifty is right at the brain crossroads himself.
“What’s more surprising is that this system breaks down at all. That is the great mystery of aging.”