EFFECTS OF ATTENTION ON VISUOMOTOR ACTIVITY IN THE PREMOTOR AND PREFRONTAL CORTEX OF A PRIMATE

We examined neuronal activity in the primate premotor (PM) and pre-fro ntal (PF) areas during a demanding spatial matching task. On each beha vioral trial, a rhesus monkey moved its forelimb when a visual stimulu s, called the ''prime stimulus,'' reappeared at a previously cued loca tion. Because it triggered a movement, the part of space cued by the p rime stimulus had to be either remembered or attended during the time between prime stimulus presentations. Between the first and second app earances of the prime stimulus, behaviorally irrelevant visual stimuli could appear at one or several locations other than that of the prime stimulus. We could thereby examine the activity that followed a stimu lus when it was attended versus when it was irrelevant and presumably unattended. We found that visuospatial attention affected neuronal act ivity in both the motor and ''nonmotor'' parts of the frontal cortex. The magnitude of attention effects exceeded that previously reported-a finding that probably resulted from the intensive attentional demands of the present task.