Notes: Summary (1) Experiments were performed to examine the influence of cutaneous information on motor cortical cells during movement in intact, awake cats. The movements investigated were locomotion and a sequence in which the animal was repeatedley lifted and dropped. Electrical stimuli to distal skin areas were delivered periodically during the movements and responses of motor cortical cells were examined. (2) The animals used in these experiments were chronically implanted with cortical microelectrodes, a pyramidal tract stimulating electrode, cutaneous stimulating electrodes in the forepaw, and a recording cuff electrode around the median nerve. EMG electrodes were implanted in several forelimb muscles and a length gauge was implanted across the elbow joint. (3) Results included in this report were obtained from three cats. The twenty-two cortical units analysed in this study (seven were PT units) were selected from a larger sample by the following criteria: 1) cutaneous receptive fields which included the distal part of the limb, 2) consistent short latency responses to electrical cutaneous stimulation and 3) spontaneous activity modulated in consistent patterns during the movement investigated. (4) Sixteen units were recorded during locomotion, 12 during the lifting and dropping cycle and 6 of these during both conditions. Most of the cells were influenced by the cutaneous input during locomotion. Three units had no response to peripheral stimulation during locomotion though they were responsive to this stimulus when the animal was sitting quietly. All the cells were responsive to the cutaneous input during the lifting and dropping cycle. (5) The responses to cutaneous stimuli were found to be modulated in relation to phases of the step cycle and the lifting and dropping cycle. In 13 units this modulation did not parallel the modulation of the units' spontaneous firing during these activities. For these units a common finding during locomotion was that the response to cutaneous stimuli increased throughout stance, reached maximum during the flexion part of the swing, and then declined to a minimum during the beginning of the next stance. During the lifting and dropping cycle, the responses were greatest when the animal was held in the air and when starting to fall, and minimal just prior to and after landing. In both movements, cutaneous responses were reduced when the limb was used to support the animal's weight. (6) There is apparently a movement phase-related modulation of cutaneous input to some motor cortical cells. This modulation of cutaneous input resembled the modulation of cutaneous reflexes during locomotion. It is suggested that some cortical cells receive excitation through cutaneous reflex pathways which may be depressed under certain conditions. This may serve as a useful mechanism in adjusting the gain of the motor output to prevent inappropriate activity during these times.

Notes: Summary Experiments were performed to examine the responses of cortical neurons in the pericruciate cortex to cutaneous afferent input from the distal forepaw. Ninty-nine cortical neurons responding to electrical stimulation of the forepaw were recorded from four cats. Their response latencies ranged from 6 to 23 ms. The units had cutaneous receptive fields which ranged in size from those restricted to one digit to those extending over the whole forelimb. They were recorded from area 4 and area 3. Intracortical microstimulation at the recording sites activated either the distal or proximal musculature of the forelimb. When the characteristics obtained from each recording site were examined as a group of features, a uniform population emerged which was significantly different from the rest of the sample. These units had 1) the shortest latency responses to distal forepaw electrical stimulation, 2) the shortest duration of evoked discharge, 3) the smallest distal cutaneous receptive fields. Such units were recorded at the border between areas 3 and 4, at sites which on microstimulation resulted in movements of the distal forepaw musculature.