RESPONSE OF CAT CORTICAL-NEURONS TO POSITION AND MOVEMENT OF THE FEMUR

The contribution of joint afferents to the response of cortical neuron s in area 3a to mechanical stimulation of the contralateral hindlimb w as evaluated in cats anesthetized with sodium pentobarbital and paraly zed with pancuronium bromide. The hindlimb projection to the pericruci ate cortex was established by recording the evoked potentials to elect rical stimulation of the sciatic nerve and some of its branches, the b iceps-semitendinosus and the quadratus femoris. Out of 169 neurons, 63 responded exclusively to cutaneous stimuli (superficial), whereas the others could be activated by local pressure of hindlimb muscles and/o r by joint rotation (deep). Deep neurons were classified as slowly ada pting (SA) or rapidly adapting (RA) units. In the neurons responding e xclusively to joint rotation, the site of the receptive field could no t be identified with certainty. In 13 deep neurons, their firing was a ffected by rotation of multiple joints of the contralateral hindlimb. In an attempt to identify the source of activation of cortical neurons , partial denervations and muscle disconnections were performed in fiv e animals to isolate and stimulate the hip capsule. In these preparati ons, in 14 of 15 cortical neurons the source of activation was localiz ed in the periarticular muscles, with no response to mechanical stimul ation of the joint capsule. Only one neuron (SA) could be selectively excited by punctate pressure on the hip capsule.Our results suggest th at in neurons of area 3a of the cat, the information about the positio n of the femur relies mainly on muscle afferents.