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

1. Records have been made from area 4 of the cerebral cortex in five conscious monkeys. The properties of 216 neurones responsive to natural stimulation of the hand and fingers have been investigated.2. 46% of these neurones responded only to cutaneous stimulation (especially light brushing across the glabrous skin) and a further 38% responded only to movement of the digits. 4% responded to brief prods of the hand. 12% of the sample responded to more than one stimulus modality.3. Many hand-input neurones, including pyramidal tract neurones, responded at short-latency (8-15 msec) to light mechanical stimulation of the hand and to weak electrical stimulation of the median nerve.4. Responsive neurones were found at all depths of the cortical grey matter. Responses of shortest latency were encountered in neurones probably located in layers IV and V.5. The behaviour of eighty hand-input neurones was analysed during a simple, stereotyped task which involved pulling a lever and collecting a food reward from a small well. For comparison, the activity of 117 neurones with inputs from the wrist, elbow or shoulder was also analysed.6. Nearly all hand-input neurones modulated their activity either 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.7. By contrast, the activity of many neurones with proximal arm (elbow, shoulder) inputs was unrelated to food retrieval and manipulation, but well related to arm movements.8. Forty-three of the eighty neurones had cutaneous input from the hand. Twenty-seven were active before hand contact. Thirty-five modulated their discharge when contact was made (twenty-one excitation, fourteen inhibition).9. Most hand-input neurones were more active during fractionated movements of the hand or fingers than during power or ball grips requiring simultaneous flexion of all digits. Neurones with glabrous inputs often showed intense activity during small, precise finger movements and during active tactile exploration without the aid of vision.10. Analysis of the discharge frequency of twenty-five hand-input neurones revealed that some (mainly non-pyramidal tract neurones) had a similar mean frequency and range of modulation during both active movement and passive stimulation. Others (mainly pyramidal tract neurones) had a greater frequency range and higher mean frequency during active than during passive movements.