Neural mechanisms of individual differences in working memory: Effects of age and processing speed

The goal of neurocognitive aging research is to elucidate neural mechanisms that lead to performance changes in individuals as they age. Compelling evidence suggests that age-related performance changes are linked to slowing of fundamental cognitive systems such as working memory (WM), yet no plausible neural mechanisms of age-related slowing have yet been identified. I will present a series of studies, using functional magnetic resonance imaging (fMRI) that suggest that age-related WM performance changes are related to changes in prefrontal cortical (PFC) function. In these studies younger and older adults performed a verbal delayed-response task with varying memory set sizes. Results from these studies indicated that older adults performed more slowly than younger adults. Importantly, individual subjects’ response speed accounted for significant proportions of age-related variance in PFC activity but memory set-size did not. For younger adults, PFC activation decreased with faster performance. The opposite activation-performance pattern was observed for older adults. Replication of this pattern when subjects performed a simple processing-speed task provide further support for the notion that that age-related cognitive slowing may be related to changes in the efficiency of PFC function.