The brain, like every other part of the body, changes with age, and those changes can impede clear thinking and memory. Yet many older people seem to remain sharp as a tack well into their 80s and beyond. Although their pace may have slowed, they continue to work, travel, attend plays and concerts, play cards and board games, study foreign languages, design buildings, work with computers, write books, do puzzles, knit or perform other mentally challenging tasks that can befuddle people much younger.
But when these sharp old folks die, autopsy studies often reveal extensive brain abnormalities like those in patients with Alzheimer's.
Cognitive reserve, in this theory, refers to the brain's ability to develop and maintain extra neurons and connections between them via axons and dendrites. Later in life, these connections may help compensate for the rise in dementia-related brain pathology that accompanies normal aging.
Cognitive reserve is greater in people who complete higher levels of education. The more intellectual challenges to the brain early in life, the more neurons and connections the brain is likely to develop and perhaps maintain into later years. Several studies of normal aging have found that higher levels of educational attainment were associated with slower cognitive and functional decline.
But brain stimulation does not have to stop with the diploma. Better-educated people may go on to choose more intellectually demanding occupations and pursue brain-stimulating hobbies, resulting in a form of lifelong learning.