SPATIOTEMPORAL DYNAMICS OF COMPONENT PROCESSES IN HUMAN WORKING-MEMORY

Working memory (WM), the ability to momentarily maintain information i n an active state, is central to higher cognitive functions. The proce sses involved in WM operate on a sub-second timescale, and thus evoked potential measures have an appropriate temporal resolution for studyi ng them. In the experiment reported here, evoked potential covariances (EPC) between scalp recording sites were computed for a task requirin g maintenance of numeric information in WM; these EPCs were compared t o those observed in a control task which had the same stimuli and resp onses but less of a WM requirement. EPC patterns differed between cond itions prior to the stimulus, and in an interval spanning the P300 pea k in the match detection trials which required response inhibition. Th e pattern of prestimulus EPCs was more complex and left-sided in the W M task, when memory codes were being maintained and responses continge nt on those codes were being prepared. P300 peak latency was 140 msec shorter in the WM task, and the P300 EPC pattern was more anterior and left-sided. In contrast, EPC patterns did not differ during early sta ges of stimulus processing or during response execution. These results suggest that distinct EPC patterns associated with WM only occur duri ng intervals in which the information in an active state is being util ized for task performance.