SUSTAINED ACTIVITY IN THE MEDIAL WALL DURING WORKING-MEMORY DELAYS

We have taken advantage of the temporal resolution afforded by functio nal magnetic resonance imaging (fMRI) to investigate the role played b y medial wall areas in humans during working memory tasks. We demarcat ed the medial motor areas activated during simple manual movement, nam ely the supplementary motor area (SMA) and the cingulate motor area (C MA), and those activated during visually guided saccadic eye movements , namely the supplementary eye field (SEF). We determined the location of sustained activity over working memory delays in the medial wall i n relation to these functional landmarks during both spatial and face working memory tasks. We identified two distinct areas, namely the pre -SMA and the caudal part of the anterior cingulate cortex (caudal-AC), that showed similar sustained activity during both spatial and face w orking memory delays. These areas were distinct from and anterior to t he SMA, CMA, and SEF. Both the pre-SMA and caudal-AC activation were i dentified by a contrast between sustained activity during working memo ry delays as compared with sustained activity during control delays in which subjects were waiting for a cue to make a simple manual motor r esponse. Thus, the present findings suggest that sustained activity du ring working memory delays in both the pre-SMA and caudal-AC does not reflect simple motor preparation but rather a state of preparedness fo r selecting a motor response based on the information held on-line.