Role of sensory feedback in the control of stance duration in walking cats.

The rate of stepping in the hind legs of chronic spinal and decerebrate cats adapts to the speed of the treadmill on which the animals walk. This adaptive behavior depends on sensory signals generated near the end of stance phase controlling the transition from stance to swing. Two sensory signals have been identified to have this role: one from afferents activated by hip extension, most likely arising from muscle spindles in hip flexor muscles, and the other from group Ib afferents from Golgi tendon organs in the ankle extensor muscles. The relative importance of these two signals in controlling the stance to swing transition differs in chronic spinal cats and in decerebrate cats. Activation of hip afferents is necessary for controlling the transition in chronic spinal cats but not in decerebrate cats, while reduction in activity in group Ib afferents from GTOs is the primary factor controlling the transition in decerebrate cats. Possible mechanisms for this difference are discussed. The extent to which these two sensory signals control the stance to swing transition in normal walking cats is unknown, but it is likely that both could play an important role when animals are walking in a variable environment.