High intensity stimuli of the skin were delivered to one hindlimb in various parts of the step cycle of decerebrate cats walking on a treadmill. Whereas the stimulated limb always flexes after the stimulation there is, in the contralateral limb, a crossed flexion response during swing or a crossed extension response during stance. The frequency distribution of the responses in contralateral flexor or extensor muscles peaks at around the onset of the respective locomotor bursts although responses can be evoked before and after that onset. In certain periods of the cycle, largely corresponding to the transition from flexor or extensor activity and vice versa, the responses can occur in either muscles. The long latencies of crossed responses are similar to that of the ipsilateral responses so that both occur approximately at the same time. The amplitude and duration of crossed responses vary according to the phase of the walking cycle. The types of responses and the overall changes in the step cycles suggest that crossed extension responses mainly serve to sustain the increased weight to the contralateral side during ipsilateral flexion whereas crossed flexion responses appear well studied to rapidly rephase the contralateral limb step cycle to that of the ipsilateral limb which is markedly perturbed by the flexion response elicited during its stance phase.
Animals Cats