The overall goal of this revised proposal is to examine the neural basis of the development of working memory and processing speed in late childhood (ages 8-12) and the persistence of individual differences in working memory and processing speed in young adults (ages 18-30). These cognitive operations have been posited to mediate developmental and individual differences in a variety of higher order cognitive abilities. Functional magnetic resonance imaging (fMRI) and volumetric and diffusion tensor imaging will be used to determine whether the same or different neural mechanisms account for child development and adult individual differences in working memory and processing speed. The investigators hypothesize that differences in function and structure of the prefrontal cortex are correlated with developmental and adult differences in working memory capacity and processing speed. They will measure function and structure (including volume and myelination) throughout the brain in order to examine the specificity of prefrontal correlations. The sample will include 60 children, 20 of whom are at each of the following ages: 8,10, and 12 years. There will also be 80 young adults, 10 to be selected in each of the four quartiles of working memory capacity. Three proposed experiments examining working memory maintenance (Exp 1) and manipulation (Exp 2) tasks and a processing speed task (Exp 3) will be conducted in two scanning sessions. For each cognitive task, they will manipulate processing demands due to inhibitory control in working memory maintenance at two ability-matched levels (good and poor) across all groups. Increasing processing demands are expected to magnify developmental and individual differences, in both behavioral performance and brain activation. They will also collect a variety of psychometric measures of working memory and processing speed in all subjects in order to examine relationships between behavioral, structural anatomical, and functional anatomical measures.
