Epidural spinal cord stimulation as an intervention for motor recovery after motor complete spinal cord injury

Abstract

Spinal cord injury (SCI) commonly results in permanent loss of motor, sensory, and autonomic function. Recent clinical studies have shown that epidural spinal cord stimulation may provide a beneficial adjunct for restoring lower extremity and other neurological functions. Herein, we review the recent clinical advances of lumbosacral epidural stimulation for restoration of sensorimotor function in individuals with motor complete SCI and we discuss the putative neural pathways involved in this promising neurorehabilitative approach. We focus on three main sections: review recent clinical results for locomotor restoration in complete SCI; discuss the contemporary understanding of electrical neuromodulation and signal transduction pathways involved in spinal locomotor networks; review current challenges of motor system modulation and future directions towards integrative neurorestoration. The current understanding is that initial depolarization occurs at the level of large diameter dorsal root proprioceptive afferents that when integrated with interneuronal and latent residual supraspinal translesional connections can recruit locomotor centers and augment downstream motor units. Spinal epidural stimulation can initiate excitability changes in spinal networks and supraspinal networks. Different stimulation parameters can facilitate standing or stepping, and it may also have potential for augmenting myriad other sensorimotor and autonomic functions. More comprehensive investigation of the mechanisms that mediate the transformation of dysfunctional spinal networks to higher functional states with a greater focus on integrated systems based control system may reveal the key mechanisms underlying neurological augmentation and motor restoration after severe paralysis.

Invasive and Non-Invasive Approaches of Electrical Stimulation to Improve Physical Functioning after Spinal Cord Injury

“…The work was based on years of animal research that demonstrated that task-specific training or neuromodulation (epidural stimulation) may restore overground mobility even in the fully transected spinal cord [74]. The findings highlighted that spinal cord circuitry has the capability to integrate afferent sensory information and execute motor outputs independent of any supraspinal control [74,75]. A recent review has provided a detailed explanation on several potential mechanisms of the effects of epidural stimulation on the sensorimotor system in persons with SCI [75].…”

“…The findings highlighted that spinal cord circuitry has the capability to integrate afferent sensory information and execute motor outputs independent of any supraspinal control [74,75]. A recent review has provided a detailed explanation on several potential mechanisms of the effects of epidural stimulation on the sensorimotor system in persons with SCI [75]. The works have gained considerable attention, especially considering the lumbosacral central pattern generators (CPGs).…”

“…The CPG is a group of neural interneurons characterized by controlled rhythmicity and likely to contribute to several functions, including fictive locomotion, reflexive actions, reciprocal patterns between agonist and antagonists' muscles, and, finally, spinal locomotion. This has led many researchers to recognize that the spinal cord is a perceptive central nervous system capable of learning, memorizing, and executing motor commands with task-specific training independent of any supraspinal control [75].…”

“…Epidural stimulation involves the application of a continuous electrical current to the lower part of the spinal cord via an electrode implanted over the dura in the epidural space. When combined with task-specific movement practice, it can improve motor function [75,79,80]. A recently completed scoping review identified the potential benefits of epidural stimulation for individuals with SCI, including reductions in pain, spasms, and spasticity, improvements in the bowel, cardiorespiratory and cardiometabolic function, and an increased upper and lower extremity function [81].…”

“…It is interesting to note that even in participants with complete SCI, full overground ambulation has been restored with epidural stimulation. The mechanisms of how epidural stimulation manages to restore sensory-motor integration to restore locomotion have yet to be deciphered [75]. One of the explanations is sensorymotor integration via the continuous activation of the CPGs.…”