changes in their nervous systems and their environments and, at the same time, both types of changes affect their ability to perform cognitive tasks. To separate the various causes of cognitive change, it is necessary to examine inter-and intraindividual differences in cognitive function both cross-sectionally and over time to identify patterns. Such examinations should highlight the roles of dynamic adaptive processes, including changes in neuronal structure and function and in behavioral and social factors (e.g., social opportunity structures, the individual's routines and physical environment, the individual's goals, and the use of social and technological supports) that codetermine an individual's ability to function effectively.
Our task has been to identify areas of opportunity in which additional research support from the National Institute on Aging (NIA) would substantially improve understanding of cognitive functioning in aging by drawing on recent developments in behavioral science, cognitive science, and neuroscience that are not yet fully applied to this subject area. As already noted, we have adopted a broad definition of cognitive function.
Our focus is on cognitive function in aging people who are not suffering from a dementia-causing disease—that is, on "normal" rather than "pathological" aging. The boundary between normal and pathological aging is hard to define. For one thing, some individuals who are aging "normally" at one point in time may later develop dementia, suggesting that their earlier ''normal" functioning was in fact compromised by preclinical signs of that dementia. For another, conditions associated with aging that are not themselves considered as cognitive pathology, such as hypertension, sensory decline, and certain cardiovascular events, may have cognitive effects, as discussed in Chapter 4. People experiencing such conditions who do not suffer from one of the dementias must be considered as aging "normally" for the purposes of research in the near term; however, research may eventually discover that for some of them, a pathological process was directly affecting their cognition. Thus, a population of "normally" aging individuals defined at one time may be determined on the basis of later research or later life events to have included some individuals whose cognition was compromised by a pathological process.
A major difficulty for our task is that there are many promising research directions from which to choose. The aging mind is a topic at the intersection of several active fields of behavioral science, cognitive science, and neuroscience within which research is continually opening new vistas. New research opportunities arise often in these fields, even without special efforts to find them. We have therefore made a special effort to identify opportunities that might not automatically flow from current lines of research. For ex-