How the Mind Ages

Aging, it is now clear, is part of an ongoing maturation process that all our organs go through. "In a sense, aging is keyed to the level of vigor of the body and the continuous interaction between levels of body activity and levels of mental activity," reports Arnold B. Scheibel, M.D., whose very academic title reflects how once far-flung domains now converge on the mind and the brain. Scheibel is professor of anatomy, cell biology, psychiatry, and behavioral sciences at the University of California at Los Angeles, and director of the university's Brain Research Institute.

Conventional wisdom has it that, as the vigor of the body declines, the power of the mind diminishes as well. Indeed, older people seem to slow down mentally; they often become garrulous, forgetful, crotchety, and some develop outright dementia.

Experimental evidence has backed up popular assumptions that the aging mind undergoes decay analogous to that of the aging body. Younger monkeys, chimps, and lower animals consistently outperform their older colleagues on memory tests. In humans, psychologists concluded, memory and other mental functions deteriorate over time because of inevitable organic changes in the brain as neurons die off. Mental decline after young adulthood appeared inevitable.

The truth, however, is not quite so simple. Some functions peak early in life, others don't get up to speed until adolescence or early adulthood. There are mental capabilities, like judgment and wisdom, that continue to improve as you grow older even as others, like short-term memory and the ability to do tasks within a set time limit, may start to decline in your 40s.

Although many mental functions actually begin to fall off or reach their peak at about age 24 to 28, adults do continue to learn, and their mental programming refines itself. What's more, research over the past decades shows that the mind constantly adjusts its way of doing things and compensates nicely for many losses in efficiency. The brain, too, is almost infinitely plastic, containing many more neurons (with more potential connections between them) than we can use. If one neuron fails, those nearby can take on its load.

Equipped with imaging techniques that capture the brain in action, Stanley Rapoport, Ph.D., at the National Institutes of Health, measured the flow of blood in the brains of old and young people as they went through the task of matching photos of faces. Since blood flow reflects neuronal activity, Rapoport could compare which networks of neurons were being used by different subjects.

"Even when the reaction times of older and younger subjects were the same, the neural networks they used were significantly different. The older subjects were using different internal strategies to accomplish the same result in the same time," Rapoport says. Either the task required greater effort on the part of the older subjects or the work of neurons originally involved in tasks of that type had been taken over by other neurons, creating different networks.

At the Georgia Institute of Technology, psychologist Timothy Salthouse, Ph.D., compared a group of very fast and accurate typists of college age with another group in their 60s. Since reaction time is faster in younger people and most people's fingers grow less nimble with age, younger typists might be expected to tap right along while the older ones fumble. But both typed 60 words a minute.

The older typists, it turned out, achieved their speed with cunning little strategies that made them far more efficient than their younger counterparts: They made fewer finger movements, saving a fraction of a second here and there. They also read ahead in the text. The neural networks involved in typing appear to have been reshaped to compensate for losses in motor skills or other age changes.

There's solid evidence that deterioration in mental functions can actually be reversed. It is certainly true of laboratory animals, probably of humans as well. Neuropsychologist Marion Diamond, Ph.D., and others at the University of California at Berkeley have shown that mental activity makes neurons sprout new dendrites with which to establish connections with other neurons. The dendrites shrink when the mind is idle.