in which age-related changes that affect cognition are occurring. This information will be important to future efforts to intervene at the molecular and cellular level, because it will tell where in the brain to look for the substrate of observed behavioral effects.

As neuroscience research attains higher levels of resolution, it will become possible to identify particular neural circuits believed to be associated with particular cognitive functions. To achieve understanding of brain-behavior links at this level, it is important to build theory and to identify or construct behavioral measures that fit the structure of cognition and can be localized with comparable resolution to neural observations. This implies a search for fine-grained measures of specific cognitive processes and of the operation of particular neural systems. It also implies a continuing co-evolution of behavioral measures and brain measures and a continuing effort to refine both kinds of measures in order to further clarify brain-behavior links.

An important point to recognize with regard to the above issues of measurement is the central role of experimental animals in research on aging. Neural observations are more feasible in animal models, and many findings are likely to generalize across species. Biological research during the past decade has shown the extraordinary extent to which cellular and molecular mechanisms are conserved through evolution. Indeed, even at the level of brain systems and brain-behavior relationships, one finds considerable parallel across species. Recent advances in molecular biology have caused the mouse to become important for behavioral studies. At the present time, one can expect useful work on brain and behavior, in the context of aging research, to be carried out in the mouse, rat, and monkey, and perhaps in other animal species as well.

Advances in Theory Development

Cognitive behavioral science is making progress on the theoretical side. An example is Baddeley's influential theory of working memory, which postulates interrelated components for speech and visual information with separate storage and rehearsal mechanisms. This theory has motivated investigations of working memory in patients (Vallar and Baddeley, 1984) and using imaging techniques (e.g., Smith and Jonides, 1997) that have supported distinctions in the theory and have identified the neural basis for hypothesized working memory mechanisms. A number of studies following the theory have investigated age differences in components of working memory (e.g., Wingfield et al., 1995).

Research based on theoretically justified measures of specific cognitive functions will make it possible to examine more closely the links between functioning of particular neural circuits and performance on the behavioral indicators, as well as between the behavioral indicators and performance of



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