Functional properties of monkey motor cortex neurones receiving afferent input from the hand and fingers

Publisher Website
Google Scholar
Abstract
Area 4 of the cerebral cortex in 5 conscious monkeys [Macaca mulatta, M. nemestrina and M. fascicularis] was recorded. The properties of 216 neurons responsive to natural stimulation of the hand and fingers were investigated. Of these neurons, 46% responded only to cutaneous stimulation (especially light brushing across the glabrous skin), 38% responded only to movement of the digits, 4% responded to brief prods of the hand and 12% responded to more than 1 stimulus modality. Many hand-input neurons, including pyramidal tract neurons, responded at short-latency (8-15 ms) to light mechanical stimulation of the hand and to weak electrical stimulation of the median nerve. Responsive neurons were found at all depths of the cortical grey matter. Responses of shortest latency were encountered in neurons probably located in layers IV and V. The behavior of 80 hand-input neurons was analyzed during a simple, stereotyped task which involved pulling a lever and collecting a food reward from a small well. The activity of 117 neurons with inputs from the wrist, elbow or shoulder were compared. Nearly all hand-input neurons modulated their activity before (48/80) or during (29/80) the retrieval of the reward which required precision grip between index finger and thumb. Many were silent during proximal arm movements and some displayed activity patterns independent of these movements. The activity of many neurons with proximal arm (elbow, shoulder) inputs was unrelated to food retrieval and manipulation, but well related to arm movements. Of the 80 neurons, 43 had cutaneous input from the hand, 27 were active before hand contact and 35 modulated their discharge when contact was made (21 excitation, 14 inhibition). Most hand-input neurons were more active during fractionated movements of the hand or fingers than during power or ball grips requiring simultanoous flexion of all digits. Neurons with glabrous inputs often showed intense activity during small, precise finger movements and during active tactile exploration without the aid of vision. The discharge frequency of 25 hand-input neurons was analyzed. Some (mainly non-pyramidal tract neurons) had a similar mean frequency and range of modulation during active movement and passive stimulation. Others (mainly pyramidal tract neurons) had a greater frequency range and higher mean frequency during active than during passive movements.