NEUROIMAGING ANALYSES OF HUMAN WORKING-MEMORY

We review a program of research that uses neuroimaging techniques to d etermine the functional and neural architecture of human working memor y. A first set of studies indicates that verbal working memory include s a storage component, which is implemented neurally by areas in the l eft-hemisphere posterior parietal cortex, and a subvocal rehearsal com ponent, which is implemented by left-hemisphere speech areas, includin g Broca's area as well as the premotor and supplementary motor areas. We provide a number of neuroimaging dissociations between the storage and rehearsal areas. A second set of studies focuses on spatial workin g memory and indicates that it is mediated by a network of predominant ly right-hemisphere regions that include areas in posterior parietal, occipital, and frontal cortex. We provide some suggestive evidence tha t these areas, too, divide into storage and rehearsal regions, with ri ght-hemisphere posterior parietal and premotor regions subserving spat ial rehearsal. In a final set of studies, we turn to ''executive proce sses,'' metaprocesses that regulate the processing of working-memory c ontents. We focus on the executive process of inhibition as it is used in verbal working memory. We provide evidence that such inhibition is mediated by the left-hemisphere prefrontal region and that it can be dissociated from verbal storage and rehearsal processes.