ROLES OF ATTENTION, MEMORY AND MOTOR PREPARATION IN MODULATING HUMAN BRAIN ACTIVITY IN A SPATIAL WORKING-MEMORY TASK

Neuronal activity of the human brain was studied with magnetoencephalo graphy (MEG) in a spatial working memory task similar to those commonl y used with nonhuman primates. The subject was required to remember ta rget positions for 3 s and make a same-different judgement with a fing er lift comparing the position of the probed target with the probe or to execute a meory-guided saccade to the probed target. In this type o f task single unit studies have shown attention-and memory-related act ivities independent of movement type during the retention interval in a large number of cortical areas of the primates, including the pariet al and prefrontal areas. Consistent with these results, there were str ong stimulus-driven transient and sustained responses and modulations of oscillatory activity during the retention period. Although we did n ot determine the source locations, coarse estimates of the currents re sponsible for the MEG signals showed activity over a wide area of the cortex, most prominently over the Rolandic, parietal and occipital are as, hut also over the frontal area. Some of the activities in these co rtical areas reflect processes that may be identified with attention a nd memory, while others were related to preparation of the overt movem ents.