Experiments with decerebrate cats during treadmill and fictive locomotion have provided much of what we know about the ways in which afferent feedback can regulate mammalian locomotion. Depending on the type of afferent and the timing of stimulus delivery during the step cycle, one can entrain the locomotor rhythm, cause a premature or delayed transition to the next step cycle phase, or enhance motoneurone activity in the on-going phase. Activation of ankle extensor group I muscle spindle or tendon organ afferents during extension simultaneously increases the duration and amount of extensor activity throughout the limb. These widespread reflex actions and the ability for prolonged afferent activation to disrupt step cycle timing and prevent the transition from stance to swing is evidence that locomotor-dependent reflexes can affect the locomotor pattern generating circuitry. As another example of how feedback from a limited subset of afferents can affect the CPG, activity in hip flexor muscle afferents plays a critical role in regulating the transition from swing to stance. Finally, activation of cutaneous afferents from the dorsum of the foot during both real and fictive locomotion evokes a corrective reflex that prevents stumbling. In this case a specialized reflex increases flexion at the hip, knee and ankle presumably by actions evoked in part through CPG circuitry without significantly affecting step cycle period. It is likely that identification of the interneurones mediating reflexes affecting pattern generating networks will provide insights into the organization of the CPG itself.

This work was supported by the Canadian Institutes for Health Research.