Relationship between the activity of precentral neurones during active and passive movements in conscious monkeys

Abstract Recordings have been made from neurones in the precentral cortex of conscious monkeys carrying out a stereotyped movement task for food rewards. The activity of each movement related neurone was investigated while the monkey performed a wide variety of movements in order to collect the food reward placed in a number of different positions. Of 362 task-related neurones, 176 neurones showed definite modulation of their discharge frequency which could be related to the performance of specific voluntary movements about one joint, or at a number of associated digit joints. These neurones could therefore be classified to have dis­charges associated with particular voluntary movements of shoulder, elbow, wrist, hand or fingers. The responses of the same neurones were then examined with natural stimulation of the skin, joints and muscles of the arm while the animal sat relaxed as it had been trained to do. 149 of the 176 neurones responded to afferent input from particular peripheral territories. 130 of the 176 neurones had afferent inputs from zones which were anatomically closely related to the joint involved in the specific active movement with which the neurone’s natural discharges were clearly associated. An analysis of the anatomical distribution in the motor cortex of the cells exhibiting given input and output associations revealed that not all the members of a restricted local population of neurones shared the same peripheral territory. When they did, the direction of movement of that territory which was associated with discharge of the cell could be the same or opposite under active and passive conditions. Moreover, not all the neurones with a particular association with active movement of a joint and an input from that same region were aggregated in the one restricted local area of the motor cortex; some members of the group sharing these input/output characteristics could be situated up to 5 mm from the main aggregation. An attempt is made to distinguish between the properties of receiving neurones and output neurones of the precentral gyrus.