It has been previously demonstrated that epidural stimulation of the posterior lumbar cord can activate the Lumbar Locomotor Pattern Generator (LLPG) and induce stepping-like movements in complete spinal cord injured subjects. In these studies, the subjects were lying in a supine position and afferent feedback input from the lower limbs was minimized. The present paper demonstrates the interaction between induced LLPG activity and manually assisted treadmill stepping in paralyzed subjects. Epidural stimulation applied at frequencies of 20-50 Hz during treadmill-stepping enhanced the responsiveness of the spinal circuits to proprioceptive feedback in generating stepping-like motor patterns. We suggest that the spinal lumbar networks can integrate and interpret both, the stimulus-evoked tonic input with a "central" code and the proprioceptive feedback input in order to generate effective loco motor patterns.
