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Brain Building

Education is the factor that has received by far the most attention among Alzheimer's disease researchers interested in cognitive reserve, because of its strong correlation with cognitive performance noted in the studies described above. However, Dr. Bennett brings a unique perspective to this field of study, and an expansive way of thinking about all the factors that might contribute to the creation of an efficient brain.

One of the out-of-the-box ways that Dr. Bennett has approached thinking about brain activity is to consider how people must develop semantic memory—generalized knowledge that does not involve memory of a specific event—each time they interact with someone they know. Consider that the brain has to work hard to help a person maintain a social network. If a man bumps into an old friend, somebody he hasn't seen in twenty years, he recalls in an instant how he knows her, whether she's married, has children, and so on. This task alone stimulates the brain. Then the old information is integrated with the new information from the current encounter, which is stored in his memory bank so he is able to call it all up again the next time he meets her. People with complex social networks are constantly engaging with others in this way, updating their brain files. Perhaps, like formal education, this stimulates the brain and creates more cognitive reserve.

It turns out that having many friends and participating in social activities have been associated with reduced cognitive decline and decreased risk of dementia in older adults. For example, the National Institute on Aging-funded Memory and Aging Project, which Dr. Bennett directs, found an association between higher levels of social engagement and better cognitive function over time.

Dr. Bennett's other major study, the Religious Orders Study, also has associated a high level of cognitive activity with reduced Alzheimer's disease risk. Investigators on that project periodically asked study participants —older nuns, priests, and religious brothers—to describe how much time they spent in seven information-processing activities: having a conversation, reading a book, listening to the radio, watching television, reading newspapers, playing puzzle games, and going to museums. After following the volunteers for four years, investigators found that the risk of developing AD was, on average, 47 percent lower for participants who did the activities most frequently than for those who did them least frequently. Other studies have shown similar results. In addition, a growing body of research, including other findings from the Religious Orders Study, has associated a higher level of education with increased memory and learning abilities, even when a person has sufficient deposition of beta-amyloid plaques to qualify for a diagnosis of AD.

Because late-life cognitive activity is likely related to lifelong engagement in cognitively stimulating activities, Dr. Bennett and colleagues examined lifelong learning and mentally stimulating activity among participants in the Rush Memory and Aging Project. After following the research volunteers for up to five years, investigators found that both current and past activities were related to risk of AD. Importantly, even after accounting for the effects of past activity, people in the bottom 10% for current activity level were nearly three times as likely to develop AD as those in the top 10% of activity. Other studies have shown that people who are bilingual or multilingual seem to develop AD at a later age than do people who speak only one language.

Although these findings are provocative, they still need to be interpreted with caution. It's not always possible to tell whether Alzheimer's disease is the cause or the consequence of limited participation in social activities. The disease develops over the course of decades before symptoms appear, and it is possible that early AD could cause a person to limit social or intellectual activities. However, Dr. Bennett did not find a relationship between participation in cognitive activity and AD pathology in the brain. This suggests that level of cognitive activity was unlikely to be a result of AD and that whatever benefit is derived from cognitive activity is likely the result of its effect on brain reserve.

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Excerpted from THE ALZHEIMER'S PROJECT: MOMENTUM IN SCIENCE, published by Public Affairs, www.publicaffairsbooks.com.