Functional neuroimaging of memory: Implications for cognitive aging

Our understanding of the ways in which changes in specific neural systems m ediate adult age differences in memory is rapidly increasing, due in no sma ll part to the advent of functional neuroimaging techniques. This article r eviews age-related changes in memory performance obtained with behavioral m easures, describes models of the neural mechanisms of memory, and derives p redictions from these models regarding age-related changes in brain activat ion patterns. The neuroimaging findings obtained to date support models emp hasizing the role of prefrontal cortex in age-related changes in memory fun ctioning, especially for episodic memory retrieval. In general, neural acti vation associated with episodic memory encoding is regionally similar for y ounger and older adults but relatively lower in magnitude for older adults. During retrieval, activation that is restricted to the right prefrontal co rtex for younger adults is more likely to be bilateral for older adults. Pr efrontal activation exhibits an age-related increase when working memory ta sks require simple storage and an age-related decrease when working memory requires higher-level executive processes. Although the evidence is limited , behavioral performance and activation patterns appear to be similar among younger and older adults on tests of semantic (context-independent) and im plicit memory. We conclude that several methodological issues, such as defi ning the relation between brain structure and function, and determining the relationship between performance and activation, are particularly importan t for understanding age-related changes. Future directions for aging resear ch include further investigation of the relation between encoding and retri eval and the identification of both spared and impaired neural systems. Mic rosc. Res. Tech. 51:75-84, 2000. (C) 2000 Wiley-Liss, Inc.