The aging mind is shaped by a conjunction of factors. These include direct changes in the brain, variations in behavioral context (for example, task structure, motives, cultural meanings, social and technological supports), and somatic events (e.g., nonneurological disease, sensory-motor changes). Each of these is driven in part by factors that change over the life course and each may affect cognitive functioning in real-life contexts. Thus, although healthy neurons and the integrity of neural systems are necessary for adequate cognitive functioning, other factors, which affect the brain only indirectly, are important as well. For instance, cultural and social supports are necessary for adequate cognitive functioning in advanced years.

Interactions and mutual causation among neural, behavioral, and somatic phenomena are important topics for study. Discoveries about neural plasticity have put an end to the notion that the brain functions only as an independent variable in brain-behavior relationships. Experience shapes the brain and thus influences cognitive functioning across the entire life span, although these effects may be particularly strong early in life. Certain somatic processes, such as cardiovascular disease and sensory-motor changes, may affect cognitive function indirectly through their direct effects on brain functioning. Systematic differences in life experiences between cultural groups may also affect cognitive aging by altering the brain. Thus, research on the aging mind includes studies to determine the health of aging neurons; the ways in which social, behavioral, and somatic variables affect neural health and cognitive structure, content, and process; and the effects of molecular, cellular, and behavioral interventions on neural health and cognitive functioning.

Adaptive processes are central to understanding the aging mind. A prevalent model has been that of more-or-less inexorable cognitive decline. Normal aging was presumed to inevitably involve loss of neural capabilities, which in turn led automatically to loss of function. The evidence indicates, however, that different cognitive functions have different life courses (Schaie, 1994, 1996; Baltes, 1997; Baltes et al., 1999). Many people retain many cognitive capabilities into very advanced years, indicating that interindividual variation exists in rates of change with aging (Hultsch et al., 1998; Schaie, 1994, 1996; Willis, 1991), although the importance of these variations is still a matter of controversy. Three explanations of the variations can be considered. Neural changes may not be as uniform or as profound as once believed; various adaptive processes at the neural, behavioral, and social levels may mitigate the behavioral effects of the neural changes that do occur; and finally, the cultural and social environments may offer opportunities for adaptation and new growth.

The role of adaptations is particularly important. Older people adapt to



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