Normal Aging of Brain Structure and Cognition: Evolutionary Perspectives

Abstract

Many aging changes in the brain are separate from clinical disease and show evidence of adaptive compensation. The many levels of compensation are illustrated with age-related changes in dopamine neurotransmitter systems, myelination, gross structure, processing speed, and performance on neuropsychological and psychometric tests in middle and older ages. Major declines in very low-level processes that are not simultaneously paralleled by performance declines may indicate compensatory mechanisms that mask prodromal dementia. These patterns of change follow a model of biologically (genetically) programmed adaptive responses to aging in brain cells. Moreover, adaptive mechanisms also interact with the individual's environment, as suggested by the role of socioeconomic status and childhood experience in risk of cognitive impairment in old age. These findings support evolutionary mechanisms of natural selection along with extensive social support in brain aging that may be unique to humans.