Limb movements generated by stimulating muscle, nerve and spinal cord.

We have compared the movements generated by stimulation of muscle, nerve, spinal roots and spinal cord in anesthetized, decerebrate and spinalized cats. Each method produced a full range of movements of the cat's hind limb in the sagittal plane against a spring load, except for stimulation of the roots. Stimulation of the dorsal roots produced movements that were mainly up and forward, whereas stimulation of the ventral roots produced complementary movements (down and backward). Results from stimulation in the intermediate areas of the spinal cord were compared to predictions of the "movement primitives" hypothesis. We could not confirm that the directions were independent of stimulus amplitude or the state of descending inputs. Pros and cons of stimulating at some sites were provisionally considered for the reliable control of limb movements with functional electrical stimulation (FES) in clinical conditions.