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.

Modularity of Endpoint Force Patterns Evoked Using Intraspinal Microstimulation in Treadmill Trained and/or Neurotrophin-Treated Chronic Spinal Cats

“…From their previous work on anesthetized spinal-intact animals, the extension movements appear to be directed backwards (Mushahwar et al 2002), although movements in all directions could be obtained in spinal-intact anesthetized animals through stimulation of the intermediate zone of the lumbar gray (Aoyagi et al 2004a). Thus the modularity in force pattern types seen in our results is similar to the modularity in movement direction seen with intraspinal microstimulation in other laboratories (Mushahwar et al 2002;Saigal et al 2004;Tai et al 2003) and the reaction forces to postural disturbances in natural behavior (Ting and Macpherson 2005;Torres-Oviedo et al 2006).…”

“…The authors do not make a distinction between the two types. In chronic spinal cats, Saigal et al (2004) showed caudal and rostral flexor movements in addition to weight-bearing extension. From their previous work on anesthetized spinal-intact animals, the extension movements appear to be directed backwards (Mushahwar et al 2002), although movements in all directions could be obtained in spinal-intact anesthetized animals through stimulation of the intermediate zone of the lumbar gray (Aoyagi et al 2004a).…”

“…Some of the effects of spinalization on motor output due to stimulation have been examined by a number of groups. The motor responses to stimulation of lumbar cord seem relatively unchanged after chronic spinalization (Barthélemy et al 2006;Saigal et al 2004) with the topographical localization of the responses being modestly affected by chronic injury (Saigal et al 2004), more significantly with chronic injury and locomotor training, and even more significantly by administration of clonidine, an ␣2-noradrenergic agonist that promotes locomotion in spinal cats (Barthélemy et al 2006).…”

Neuroprosthetic technology for individuals with spinal cord injury

“…Restoration of locomotion through ISMS has been pursued more aggressively. [60][61][62][63] ISMS implants in these studies typically consist of arrays of up to 16-24 platinum-iridium microwires, 30 μm in diameter implanted into the lumbar enlargement and targeting hindlimb motoneuron pools in the ventral horn of the spinal cord. ISMS is capable of selectively activating muscles depending on which electrode is stimulated 60,64 allowing for generation of specific movements and minimizing unwanted contractions of nearby muscles.…”

Role of electrical stimulation for rehabilitation and regeneration after spinal cord injury: an overview

“…Experimental models of FES systems with implantable electrical stimulators and portable microprocessors are under development [20,85]. Another emerging paradigm is intraspinal micro-stimulation (ISMS), where the spinal-cord-locomotor-circuits called Central Pattern Generators (CPG) are directly tapped for stimulation and restoration of limb movements [75]. Future work on these neural prosthetic devices is also focusing on decoding the intended motion trajectories from the cerebral motor cortex and using this signal to control the FES devices.…”