Intraspinal microstimulation generates functional movements after spinal-cord injury

Abstract

Restoring locomotion after spinal-cord injury has been a difficult problem to solve with traditional functional electrical stimulation (FES) systems. Intraspinal microstimulation (ISMS) is a novel approach to FES that takes advantage of spinal-cord locomotor circuits by stimulating in the spinal cord directly. Previous studies in spinal-cord intact cats showed near normal recruitment order, reduced fatigue, and functional, synergistic movements induced by stimulation through a few microwires implanted over a 3-cm region in the lumbosacral cord. The present study sought to test the feasibility of ISMS for restoring locomotion after complete spinal-cord transection. In four adult male cats, the spinal cord was severed at T10, T11, or T12. Two to four weeks later, 30 wires (30 microm, stainless steel) were implanted, under anesthesia, in both sides of the lumbosacral cord. The cats were then decerebrated. Stimulus pulses (40-50 Hz, 200 micros, biphasic) with amplitudes ranging from 1-4x threshold (threshold = 32 +/- 19 microA) were delivered through each unipolar electrode. Kinetics, kinematics, and electromyographic (EMG) measurements were obtained with the cats suspended over a stationary treadmill with embedded force platforms for the hindlimbs. Phasic, interleaved stimulation through electrodes generating flexor or extensor movements produced bilateral weight-bearing stepping of the hindlimbs with ample foot clearance during swing. Minimal changes in kinematics and little fatigue were seen during episodes of 40 consecutive steps. The results indicate that ISMS is a promising technique for restoring locomotion after injury.