Modulation of preparatory neuronal activity in dorsal premotor cortex due to stimulus-response compatibility.

1. Neuronal activity was recorded in the dorsal premotor cortex (PMd) of two monkeys performing a multidirectional, instructed-delay (ID) reaching task in which visuospatial cues signaled the direction of movement either congruent with the instruction cue ("direct-delay" trials, DD) or redirected 180 degrees opposite to the cue ("redirected-delay" trials, RD). Therefore, this task had two degrees of stimulus-response (S-R) compatibility because in one-half of the trials the spatial attributes of the visual cue were incongruent with those of the intended movement. 2. The majority of PMd cells discharged both at short latency to the RD or DD cues and subsequently with sustained activity during the remaining ID period (IDP). The earliest responses (< 250 ms) in both DD and RD trials covaried with cue location and so could be either a "visuospatial" response or a neuronal correlate of the selection of action with highest S-R compatibility, namely move to the stimulus. In contrast, later IDP activity usually covaried with the direction of movement signaled by the cues, independent of their spatial location, supporting the hypothesis that IDP discharge in PMd ultimately encodes attributes of intended reaching movements.