In studies of more than 350 men and women between the ages of 20 and 90, Denise Park, who directs the Center for Aging and Cognition at the University of Michigan Institute for Social Research (ISR) found that mental aging is a slippery slope, with continuous declines in processing power starting as soon as our 20s.
This gradual reduction in cognitive capital is not really noticeable until the loss is substantial enough to affect everyday activities. "Younger adults in their 20s and 30s notice no losses at all, even though they are declining at the same rate as people in their 60s and 70s, because they have more capital than they need," says Park, who appears in "The Secret Life of the Brain," a new PBS series funded by the National Science Foundation.
By the time people are in their mid-60s, Park says, the continuous decreases in cognitive abilities may become noticeable. Just when most people are becoming more frequent consumers of medical services, they begin to notice that they are having more trouble remembering and learning new information.
Older people are also much more susceptible to memory distortions such as the "illusion of truth" and the "paradox of repeated denial." Older men and women are more likely to recall false information as being true, Park explains, and the more warnings they hear about a bogus medical claim---that shark cartilage cures arthritis, for example---the more likely they are to believe that the claim is true. The bogus information feels familiar if it has been heard often, and thus it seems true. Younger adults can remember that the information is familiar, but they also remember hearing that it is false.
But there is good news, too. An increase in experience and general knowledge, as measured by vocabulary, compensate for many of the memory losses says Park, with the crossroads coming around the age of 50---traditionally considered the beginning of wisdom.
With a grant from the National Institute on Aging, Park is now using neuroimaging techniques such as functional magnetic resonance imaging (fMRI) to study what goes on in the brains of younger and older minds at work. By linking behavioral testing and neuroscience, she is studying what parts of the brain older adults use for different types of mental tasks compared to younger adults, and what patterns of brain activation high-performing older adults show compared to their lower-performing peers.
"Cognitive performance is a direct result of brain activity and brain structure," park says, "much like cardiovascular fitness relates to our ability to exercise and perform physical tasks. Only 40 years ago, we had little understanding of how smoking and cholesterol levels were related to cardiovascular health," Park says. "It's likely that just as diet and exercise help to keep our bodies fit and healthy, we'll find ways to improve the functioning of our aging minds."