Can the mammalian lumbar spinal cord learn a motor task ?

Progress toward restoring locomotor function in low thoracic spinal transected cats and the application of similar techniques to patients with spinal cord injury is reviewed. Complete spinal cord transection (T12-T13) in adult cats results in an immediate loss of locomotor function in the hindlimbs. Limited locomotor function returns after several months in cats that have not received specific therapies designed to restore hindlimb stepping. Training transected cats to step on a treadmill for 30 min.d-1 and 5 d.wk-1 greatly improves their stepping ability. The most successful outcome was in cats where training began early, i.e., 1 wk after spinal transection. Cats trained to stand instead of stepping had great difficulty using the hindlimbs for locomotion. These effects were reversible over a 20-month period such that cats unable to step as a result of standing training could be trained to step and, conversely, locomotion in stepping-trained cats could be abolished by standing training. These results indicate that the spinal cord is capable of learning specific motor tasks. It has not been possible to elicit locomotion in patients with clinically complete spinal injuries, but appropriately coordinated EMG activity has been demonstrated in musculature of the legs during assisted locomotion on a treadmill.