A reappraisal of reflex stepping in the cat.

1. In re-evaluating Sherrington's experiment in which deafferented muscles in decerebrated cats ;stepped', we recorded from L5 ventral roots, a chief supplier of the major extensors of the hind legs, during stimulation of the common peroneal nerves. The extensor muscles had been denervated by appropriate dorsal root sections; the cats had been paralysed with a neuromuscular blocking agent.2. Response versus interval curves were constructed using 1 Hz stimulation. When stimulation of one peroneal preceded another, the responses ipsilateral to the second stimulation were facilitated at testing intervals of -2 to 10 msec, and inhibited at intervals of 30-400 msec.3. Responses from the L5 ventral roots mimicked ;stepping', waxing and waning at 1 Hz, only when 1 Hz was the best frequency for stimuli delivered to the two common peroneals (e.g. 24 and 25 Hz). When both sides were stimulated at the same frequency, no periodic changes in response amplitudes were seen.4. It was concluded that the apparent ;stepping' in deafferented muscles seen by Sherrington may have been due to differences in frequency of the two inductoria he used to stimulate the peroneals. We found no evidence of central timing of a pattern corresponding to walking.