Many people are found to have the neural ravages of Alzheimer’s disease upon autopsy—but they never showed the symptoms while they were alive. How can this be? It turns out that these people continued to challenge their brains into old age by staying active in their careers, doing crossword puzzles, or carrying out any other activities that kept their neural populations well exercised. As a result of staying mentally vigorous, they built what neuropsychologists call cognitive reserve.
