Secret Life of the Grown-Up Brain (13 page)

The brain, as we’ve said, is made up of gray matter—the neuron cell bodies—and white matter, the long arms of the neurons that extend throughout the brain, sending signals from one neuron to another. As we age, the arms are coated in that sheath of fat called myelin. That fatty layer allows the signal to move much faster and be timed more accurately.

Overall, myelin increases up to the fourth, fifth, or even sixth decade. But Moss and others have discovered that starting in middle age, in some people—and in some monkeys—it can also start to erode in selective areas.

In most cases during that time, such erosion is meaningless—the decreases are still outweighed by the increases and brains function better than ever. But in a few middle-aged monkeys Moss found net decreases in white matter. And he now has preliminary data showing that those monkeys that have the most negative changes in their white matter do the worst in the card-sorting games.

At this point, much is still unknown. It may be that while overall myelin increases are occurring and helping the brain operate, decreases in certain areas, such as the frontal lobes, whose rich connections need the highest efficiency for processing, may prove detrimental. It’s still unclear why some brains manage to keep up repairs and some don’t.

In any case, Moss was taken aback—and somewhat dismayed—to see any such problems in the brains of some middle-aged monkeys because these structural declines had not been detected before. The “findings of a marked impairment . . . in monkeys of middle age was initially of some surprise . . . very little is known about the age of onset of cognitive decline. The study demonstrated that middle-aged monkeys, as young as 12 years of age (equivalent to approximately 36 years in humans) already show impairment . . . deficits in EF [executive function] may occur earlier in the aging process than previously thought,” Moss wrote rather depressingly when his first data was published in 2006.

What’s more, over the past few years a clearer picture of how certain defects occur in the brains of humans has also started to emerge, and not all the news is good there, either. For this news we have no one to thank more than Naftali Raz, a neuroscientist at the Institute of Gerontology at Wayne State University in Detroit, who has become an expert in the details of brain decline and aging.

The only working neuroscientist I ran across whose papers are sprinkled with quotes from Sophocles (“For the gods alone there comes no old age, nay nor even death; but all other things are confounded by all-mastering time,” from
Oedipus at Colonus
), Raz has a succinct and downright scary way of describing what is happening in our aging brains. For instance, in a review of the scientific literature in 2006 with Karen M. Rodrigue entitled “Differential Aging of the Brain: Patterns, Cognitive Correlates and Modifiers,” he wrote:

Overall, in fact, Raz has estimated that our brains shrink by about 2 percent a decade as we age. He and others talk of a “dark side to plasticity,” which means that the areas of our brains that change the most during our lives, those that are the most sensitive to our environments—our valuable frontal lobes—could potentially suffer the most in the aging process.

But as dire as all these descriptions may be, Raz and Moss join with most other neuroscientists working today to stress that the main characteristic of the brain as it ages, and in particular the middle-aged brain—according to all we know now—is not universal decline but variability.

Moss, who was so surprised to find fairly significant declines in some middle-aged monkeys, was just as surprised to find out that the monkeys’ brains at midlife were both “mostly all right” and highly “scattered” in terms of white matter loss as well as performance on mental tests. So what is “normal” remains up for grabs—which, again, looked at one way, is very good news.

“In the end, we had to divide the group into successful and less successful agers,” Moss told me. “There clearly are these pristine agers who, even in old age, seem to be doing fine. It could be that they adapt better.”

And we are beginning to find out what is most detrimental to our brains. Even if certain diseases are not yet evident, they may still, even at very early stages, be affecting them.

“There are a lot of individual differences in cortical shrinkage rates plus there are a lot of factors other than aging that cause and influence it,” Raz wrote in his latest e-mail to me. “For example, vascular disease and cardiovascular risk factors such as hypertension (even relatively mild and responsive to medication) affect the prefrontal cortex and the hippocampus, both ‘age sensitive’ structures.”

But he also is quick to add that overall, because normal levels of decline—the kind most of us experience if we’re generally healthy—in middle age appear to be relatively small, for a long span of time in our modern middle age, all this might not matter all that much.

Even more important, scientists now know for certain that large numbers of neurons do not die off. The fundamental building blocks of our brains stay put. While “age-related differences in regional brain volumes and integrity of the white matter are associated with cognitive performance,” Raz pointed out recently, a “review of the literature reveals that the magnitude of the observed association is modest.” And, since our brains do not necessarily age in exactly the same way—and do not include a wholesale die-off of neurons—Raz sees promise, precisely because of the striking variability that he and others have found in middle age.

“Aging—a biological companion of time—spares no organ or system and in due course affects everything, from cell to thought,” Raz has written. “[But] the pace of aging varies among individuals, organisms, organs and systems. And the very existence of such variability merits some measure of hope. If the positive extreme of healthy aging can be made more prevalent and if its worst and most negative expression can be delayed if not completely eliminated, the viable and enjoyable segments of the life can be prolonged into the later decades of the lifespan. In other words, successful aging enjoyed by relatively few may become the norm.”

And while this may be taking things too far for some, there are even hints that, in a few instances, a little age-related brain decline—even in the area of focus—may work in your favor.

The science on this is in its infancy, but some recent studies have shown that letting some irrelevant information sneak into our brains can actually prove useful at times. If older people are asked to read passages that are interrupted with unexpected words or phrases, they read much more slowly than college students. But later, when both groups are asked questions whose answers depend on those distracting words and phrases, the older people are much better at solving the problem. As we age, we seem to be able to grasp the big picture better. But since our brains are also more easily distracted—when we are not asked to focus on underlying meanings—we let in random information that, while it can be an interference, can also at times prove handy. In these studies, the older people came up with the right answer precisely
because
they had seemingly irrelevant information stuffed somewhere in their brains.

A broader, less focused attention span, says Lynn Hasher, a neuroscientist at the University of Toronto, who is leading much of this new work, may allow a middle-aged person to know more about a situation—at times a real benefit in an often chaotic world where it’s not always clear what will be pertinent in the end. Maybe there’s a seemingly useless piece of information in a memo that later has meaning. Maybe while listening to another person speak, your older brain cells—wandering around here and there—notice what’s happening on the sidelines. Maybe that the person is yawning or fidgeting—tidbits of information that could help you more fully evaluate that person later on.

Indeed, other studies have shown that when an older person meets someone for a second time, she already has a great deal more peripheral information, gathered unwittingly from the first meeting, than a younger person has. As Hasher says, a brain may be a little fuzzy on some details (a name, perhaps?), but may subconsciously register other information that proves to be more crucial—this person seems confident or looks shifty, for instance.

“It’s not that people are doing this on purpose and saying, ‘Oh, that might be relevant later on, I better pay attention to that,’ ” Hasher explained to me when I spoke to her about all this. “Essentially, it’s like being on autopilot. It just happens. But in the everyday world, I think we overestimate the importance of deliberately doing things and we underestimate the importance of the automatic things we do. That’s what keeps us from tripping, from walking into walls.”

Hasher, who is sixty-three, concedes that it is not always a benefit to be on autopilot, when you have to drive on the crowded freeway or watch a toddler. But still, in more situations than we realize, this wider perspective—this lack of filtering—may help, not hurt.

“The full story is not in yet but it is amazing,” said Hasher recently, adding, as she summed up the latest research, “These findings highlight the notion that cognitive aging is characterized by both losses and gains, and that whether to consider reduced inhibitory control as a help or a hindrance depends entirely on the situation.”

What’s more, there’s also the suggestion that this less-than-straight-arrow attention can sometimes lead to art. Studies have shown that those brains that block out less tend to have more creative ideas. As Hasher says, if one part of creativity is “putting normally disassociated ideas together,” then an older brain could, almost by its very nature, be more likely to come up with something quirky, new, even beautiful.

Jacqui Smith, a longtime researcher now at the University of Michigan, agrees that a tendency toward distraction can, in the right context, lead to wonderful things. “If you don’t focus on one central thing, if you are thinking of all sorts of different things at once, sometimes you can come up with new associations. It’s hard to measure, but this is divergent thinking; this is creative thinking. And if you’re lucky, you get a true insight, something brand new.”

Not along ago, after I told a friend, a poet who had just turned fifty, about the link between distraction and creativity, she just looked at me and laughed. A growing ability to daydream? No problem. Mind wandering and linking odd things together in new ways. No problem. “That’s not all bad, you know,” she said. “In fact, that’s all very, very
good
for poetry.”

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.