Discharge properties of area 5 neurones during arm movements triggered by sensory stimuli in the monkey.

Unitary discharge was recorded from 157 cells in area 5 of 2 monkeys trained to perform rapid movements of the contralateral arm. Ninety-six cells were task-related. The earliest movement-related modulation in discharge for the large majority of cells (92%) followed the onset of electromyographic (EMG) activity. The discharge pattern of almost all units for which discharge was recorded during movements in opposite directions varied with direction, most often in a nonreciprocal manner. Discharge was correlated with peak velocity in 23% of the excited cells (n = 52). Almost the entire population of cells correlated with velocity were located in the upper part of the anterior bank of the intraparietal sulcus, suggesting that there may be at least two different functional subregions within the arm representation of area 5. Forty percent of the movement-related units had a short latency response to a small, brief perturbation of the elbow which served as one of the movement cues. These sensory responses were labile, not being present in every trial for a large number of cells. Thirty-six percent of the perturbation-sensitive cells were classified as reaction time (RT)-dependent on the basis of a correlation between RT and either the magnitude or the frequency of occurrence of the response. The response was clearly dependent on the subsequent motor response being absent when movement was extinguished. This dependence of the sensory response on the subsequent movement is a property which might represent a neural substrate for somatic sensory attention. The results also support the idea that the RT-dependent cells may be involved in the initiation of the shortest RT movements in response to the somaesthetic cue.