Neural implications of different profiles between treadmill and overground locomotion timings in cats.

A cinematographic comparison of treadmill and overground performances by the cat revealed considerable flexibility in the neural control program for locomotion. For the single limb's step cycle, swing duration (time foot is off the surface) was approximately equal in both situations, as has been found previously. Subcomponents of the swing (flexion duration and timings between joints during the transition from flexion to extension) differed, however. Interlimb timings also responded to situation. The interval between touchdown of one hindlimb and the ipsilateral forelimb was reduced for treadmill stepping. An ipsilateral coupling interval also differed that had been previously reported to involve propriospinal activity, the time for onset of extension during the swing phase of the hindlimb to the onset of flexion at the beginning of the swing phase in the forelimb. Segmental afferent input, visual and other suprasegmental inputs, and motivational variables probably all contribute to the separation of treadmill and overground timing profiles.