This Is Your Brain. Aging

This Is Your Brain. Aging. Science is reshaping what we know about getting older. (The news is better than you think.)

Over the years, Timothy Salthouse has tested more than 8,000 people in his lab at the University of Virginia, assessing their memories, problem-solving skills, and other mental functions to see how the brain fares with age. The results have been predictably dismal: after age 25 or so, it's pretty much all downhill. (No news there: Plato wrote that when a man grows old, he "can no more learn much than he can run much.") But something bothered Salthouse about the results, and on a late spring day in his office at the Russell Sage Foundation on New York's Upper East Side, where he has been a visiting scholar this year, he whips out a graph that captures the paradox.

The graph shows two roller-coastering lines. One represents the proportion of people of each age who are in the top 25 percent on a standard lab test of reasoning ability—thinking. The other shows the proportion of CEOs of Fortune 500 companies of each age. Reasoning ability peaks at about age 28 and then plummets, tracing that well-known plunge that makes those older than 30 (OK, fine, 40) cringe: only 6 percent of top scorers are in their 50s, and only 4 percent are in their 60s. But the age distribution of CEOs is an almost perfect mirror image: it peaks just before age 60. About half are older than 55. And the number under 40 is about zero.

One can make a cheap joke out of this (so that's why AIG, GM, Lehman, et al. tanked: the smartest people weren't running them), but Salt-house deduces more counterintuitive, and hopeful, lessons. The first is that in real life, rather than in psych labs, people rely on mental abilities that stand up very well to age and discover work-arounds for the mental skills that do fade. The second is that some mental abilities actually improve with age, and one of them may be the inchoate thing called wisdom, which is not a bad thing to have when running a company. Little of the gloom-and-doom conventional wisdom about what happens to the brain as we age, says Salthouse, "is based on well-established empirical evidence." Instead, he says, much of it seems to be "influenced as much by the authors' preconceptions and attitudes as by systematic evaluation" of solid data.

Insights like that are producing a dramatic, and hopeful, rethinking of what happens to the mind and brain as we age. Some of the earlier bad-news findings are being questioned as scientists discover that the differences between today's 20-year-old brains and 80-year-old brains reflect something other than simple age, and instead have to do with how people live their lives. And a deeper understanding of normal cognitive aging is producing interventions that, because they target the cell-level brain changes that accompany aging, promise to be more effective than memory exercises and crossword puzzles.

Take the claim that brain volume shrinks beginning in our 30s. Earlier studies suggested that the prefrontal cortex (just behind the forehead) takes the greatest hit; this is the region responsible for executive function such as forethought, reasoning, and "fluid" intelligence—the ability to figure out, for instance, which letter best continues the sequence G-B-F-C-E. But those data, it turns out, may be skewed by the inclusion of people who have very early dementia—so early that they have no symptoms, explains neuroscientist John Morrison of Mount Sinai School of Medicine in New York, but still have neuronal loss and thus volume loss in their prefrontal cortex. If only truly healthy people were studied, there might be no such volume loss, he says.

Earlier studies also found that myelination, the fatty insulation around neurons, peaks in our late 20s and then declines. Because myelin allows electrical signals to travel through the brain more quickly and efficiently, its loss means it takes longer to connect a face with a name, a book with an author, or any other facts. Its loss also makes the brain "noisier," explains neuroscientist Henry Mahncke of Posit Science: "It's like a radio that is no longer precisely tuned to a station. It takes the brain more effort to find that signal, and that takes resources away from memory and thinking." But myelination loss, according to new research, should come with an asterisk. Most of it seems to occur on one specific part of neurons—the part responsible for learning new things. The part responsible for long-term memory shows no such loss. ( )

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