Premotor cortex neurons in macaques: activity before distal and proximal forelimb movements.

Single unit activity was examined in the premotor cortex of three awake, behaving macaque monkeys. Premotor cortex (PM) neurons were found to be active in association with a movement involving specifically the distal forelimb. Other PM neurons were active in relation to more proximal forelimb movements. The spatial distribution of neurons related to distal movements differed from that of neurons related to proximal forelimb movements, the former being focused at a postarcuate region near the genu of the arcuate sulcus and the latter being shifted more posteromedially. The distal movement was triggered by one of the three sensory signals: visual, auditory, and vibrotactile. Of 190 PM neurons related to the distal forelimb movements, 123 (65%) showed similar premovement activity changes irrespective of the modality of the triggering signal. However, a number of neurons (35%) responded preferentially to one or two of the three signals. The modality-specific activity before movements distinguishes PM from the caudally adjacent primary motor cortex.