Brain reserve and the clinical expression of Alzheimer's disease.

Prospective clinicopathologic studies show that a large proportion of older, nondemented individuals have sufficient numbers of plaques and tangles to meet neuropathologic criteria for Alzheimer's disease (AD). One explanation for this finding is that these individuals had greater brain reserve, which buffered clinical expression of the disease. Three types of brain reserve are discussed: (1) the number of neurons and/or the density of their interconnections in youth, (2) the collection of cognitive strategies for solving problems and taking neuropsychological tests, and (3) the amount of functional brain tissue remaining at any age. Evidence is presented showing that brain reserve reduces clinical expression of AD and can be altered through several means, including early-life nutrition, prevention of cerebrovascular disease and intellectual stimulation.