TEMPORAL DYNAMICS OF BRAIN ACTIVATION DURING A WORKING-MEMORY TASK

Working memory is responsible for the short-term storage and online ma nipulation of information necessary for higher cognitive functions, su ch as language, planning and problem-solving(1,2). Traditionally, work ing memory has been divided into two types of processes: executive con trol (governing the encoding manipulation and retrieval of information in working memory) and active maintenance (keeping information availa ble 'online'). It has also been proposed that these two types of proce sses may be subserved by distinct cortical structures, with the prefro ntal cortex housing the executive control processes, and more posterio r regions housing the content-specific buffers (for example verbal ver sus visuospatial) responsible for active maintenance(3,4). However, st udies in non-human primates suggest that dorsolateral regions of the p refrontal cortex may alsb be involved in active maintenance(5-8). We h ave used functional magnetic resonance imaging to examine brain activa tion in human subjects during performance of a working memory task. We used the temporal resolution of this technique to examine the dynamic s of regional activation, and to show that prefrontal cortex along wit h parietal cortex appears to play a role in active maintenance.