Locomotor-related neuronal discharges in cat motor cortex compared with peripheral receptive fields and evoked movements.

Discharge patterns of motor cortical neurones in cats walking steadily on a moving belt have been compared with other functional characteristics of the neurones. In forelimb motor cortex rhythmic discharges occurred in cells with peripheral receptive fields in all parts of the contralateral forelimb and also in cells with no discernible receptive field. Cells discharging at similar times during the step cycle often had very different receptive fields and cells with similar receptive fields (including neighbouring cells) could discharge at similar or at quite different times. In cells with a cutaneous receptive field including the forefoot the discharges during locomotion remained rhythmic (and their phasing relative to the step cycle was unchanged) when the response to mechanical stimulation in the receptive field was temporarily much reduced or abolished by local anaesthesia of the skin. The proportion of neurones showing accelerated firing during different parts of the step cycle fluctuated more for antidromically identified pyramidal tract neurones (p.t.n.s) than for non-p.t.n.s and was highest during the second half of stance in the contralateral forelimb and lowest during swing. When the neurones were subdivided according to the movement evoked by threshold electrical stimulation through the micro-electrode, p.t.n.s and non-p.t.n.s recorded by electrodes evoking elbow flexion showed a wide variety of discharge patterns. For p.t.n.s the discharge rate reached an average of 69 impulses/s during late stance and declined to an average of 26 impulses/s during swing.