Contribution of sensory feedback to the generation of extensor activity during walking in the decerebrate cat

In this investigation we have estimated the afferent contribution to the ge neration of activity in the knee and ankle extensor muscles during walking in decerebrate cats by loading and unloading extensor muscles, and by unila teral deafferentation of a hind leg. The total contribution of afferent fee dback to extensor burst generation was estimated by allowing one hind leg t o step into a hole in the treadmill belt on which the animal was walking. I n the absence of ground support the level of activity in knee and ankle ext ensor muscles was reduced to similar to 70% of normal. Activity in the ankl e extensors could be restored during the "foot-in-hole" trials by selective ly resisting extension at the ankle. Thus feedback from proprioceptors in t he ankle extensor muscles probably makes a large contribution to burst gene ration in these muscles during weight-bearing steps. Similarly, feedback fr om proprioceptors in knee extensor appears to contribute substantially to t he activation of knee extensor muscles because unloading and loading these muscles, by lifting and dropping the hindquarters, strongly reduced and inc reased, respectively, the level of activity in the knee extensors. This con clusion was supported by the finding that partial deafferentation of one hi nd leg by transection of the L-4-L-6 dorsal roots reduced the level of acti vity in the knee extensors by similar to 50%, but did not noticeably influe nce the activity in ankle extensor muscles. However, extending the deaffere ntation to include the L-7-S-2 dorsal roots decreased the ankle extensor ac tivity. We conclude that afferent feedback contributes to more than one-hal f of the input to knee and ankle extensor motoneurons during the stance pha se of walking in decerebrate cats. The continuous contribution of afferent feedback to the generation of extensor activity could function to automatic ally adjust the intensity of activity to meet external demands.