Reversal of sign of long spinal reflexes dependent on the phase of the step cycle in the high decerebrate cat.

Reversal of the sign of long ascending and descending spinal reflexes dependent on the phase of the step cycle has been shown in the high decerebrate cat. Electrical stimuli were applied to the skin over the dorsum of the metacarpals and metatarsals and the effects were recorded in the corresponding hindlimb or forelimb of the same side. Stimulation generally evoked an increase in activity of flexor or extensor muscles shortly before, and during, activity of the muscle. Inhibition of a muscle occurred when its activity overlapped with the activity of an antagonist muscle. From the latencies it was concluded that at least the early components of the long reflex responses are due to spinal mechanisms. In the stimulated limb the activity of flexor and extensor muscles was also modulated in a phase dependent manner. No consistent long spinal responses to skin stimulation were obtained in high spinal cats during stepping. Electrical stimulation of cutaneous nerve trunks in decerebrate preparations during stepping gave variable though phase dependent long spinal reflex effects.