| Working memory is a multicomponent system that supports the temporary maintenance and manipulation of information needed to perform higher cognitive tasks. Traditionally, working memory has been divided into slave system components responsible for maintenance of visual and phonological information and the central executive (CE) component responsible for attentional control and manipulation of this information. Three studies investigated the neuropsychological underpinnings and behavioral correlates of the CE. Study 1 utilized fMRI to uncover those regions involved in CE performance. A maintenance-only condition was subtracted from a maintenance-plus-manipulation condition to reveal regions involved in or CE functioning. Results indicate a distributed network responsible for CE task performance. Study 2 examined the correspondence between two tests of working memory employed in neuroimaging, the Sternberg and N-back test, and other psychometric tests of working memory, speed of Processing, and reasoning. Results indicate a strong relationship between N-back performance and these tests of working memory and speed of processing, thus validating N-back as a measure of working memory. A subset of high and low working memory span subjects in Study 2 were selected to participate in Study 3. Selection was based on their combined performance on two of the working memory tasks, computation span and listening span. Research suggests that individual differences in working memory are largely indicative of CE functioning. Study 3 examined the neural basis of these individual differences in an effort to uncover regions involved in CE functioning. Results indicate a distributed network of regions involved in task (N-back) performance. Individual differences occurred in a subset of these regions; greater levels of activation were observed for low-span, compared to high-span, participants in inferior middle frontal regions and cerebellum. These differences were magnified as the task demands increased. In addition, there were nonsignificant trends of greater activation in low-span than high-span participants in all but two (the left and right insula/caudate) of the eleven regions of interest. This provides support for theories of neural efficiency. The implications of these studies for CE functioning are discussed. |
