search, along with continuing research with well-established methods. We therefore recommend that the initiative emphasize three method-based research strategies and their integration.

1. Relating high-resolution measures of neural functioning to measures of cognitive functioning in the aging mind.

The research initiative should support investigator-initiated research that will measure and analyze the reciprocal relations between brain and cognition. This research should utilize the new high-resolution techniques for measuring neural functioning and should link these observations to measures of cognitive functioning that are capable of isolating specific mental operations. The research will investigate age differences in the cortical components and behavioral indicators of cognitive processes as well as the effects of interventions and experience on cortical organization and behavior.

For this research approach to achieve its potential, the research initiative should support studies that address key methodological issues associated with brain imaging techniques. One such issue that requires immediate research is the decoding of the vascular signal of fMRI in ways that allow meaningful comparisons across the life span. As is well known, fMRI signals measure neural function indirectly by measuring blood flow; because blood flows differentially to active regions of the brain, the fMRI is presumed also to reflect neural activity (Le Bihan and Karni, 1995). However, the precise correlation between neural activity and the vascular signal is not known, and it may vary with age because of atrophy and other neuronal changes related to aging, as well as changes in vascularization (D'Esposito et al., 1999; Taoka et al., 1998). Eventually, longitudinal studies with humans may aid interpretation. For the next decade or more, however, the best source of insight may be information from animals, particularly the awake, behaving monkey, in which the relationship between single unit activity and the fMRI signal can be directly explored in the same tasks (Albright, Appendix G). Recently, the feasibility of this approach was demonstrated in the monkey (Stefanacci et al., 1998), and an improved technique for doing such work was demonstrated in monkeys using a custom-designed, vertical bore magnet that allows the monkey to sit in a conventional primate chair within the magnet (Logothetis et al., 1999).

Another methodological problem deserving immediate attention concerns ways to improve the correspondence between behavioral measures and neural observations, such as those that new measurement techniques can provide. Recent advances in the behavioral measurement of specific cognitive functions have already been noted. The research initiative should support studies to identify or develop focused behavioral indicators that connect closely to high-resolution neural observations. It is to be expected that simple behaviors will yield more easily to this approach than complex ones, which are more likely to involve distributed neural activity.

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