MODULATION OF PREPARATORY NEURONAL-ACTIVITY IN DORSAL PREMOTOR CORTEXDUE TO STIMULUS-RESPONSE COMPATIBILITY

1. Neuronal activity was recorded in the dorsal premotor cortex (PMd) of two monkeys performing a multidirectional, instructed-delay (ID) re aching task in which visuospatial cues signaled the direction of movem ent either congruent with the instruction cue (''direct-delay'' trials , DD) or redirected 180 degrees opposite to the cue (''redirected-dela y'' trials, RD). Therefore, this task had two degrees of stimulus-resp onse (S-R) compatibility because in one-half of the trials the spatial attributes of the visual cue were incongruent with those of the inten ded movement. 2. The majority of PMd cells discharged both at short la tency to the RD or DD cues and subsequently with sustained activity du ring the remaining ID period (IDP). The earliest responses (<250 ms) i n both DD and RD trials covaried with cue location and so could be eit her a ''visuospatial'' response or a neuronal correlate of the selecti on of action with highest S-R compatibility, namely move to the stimul us. In contrast, later IDP activity usually covaried with the directio n of movement signaled by the cues, independent of their spatial locat ion, supporting the hypothesis that IDP discharge in PMd ultimately en codes attributes of intended reaching movements.