Harnessing Neuroplasticity of Postural Sensorimotor Networks Using Non-Invasive Spinal Neuromodulation to Maximize Functional Recovery After Spinal Cord Injury

It has been demonstrated that the human lumbosacral spinal cord can be neuromodulated with epidural (ESS) and transcutaneous (TSS) spinal cord stimulation to enable recovery of standing and volitional control of the lower limbs after complete motor paralysis due to spinal cord injury (SCI). The work proposed herein will examine and identify distinct electrophysiological mechanisms underlying transcutaneous spinal stimulation (TSS) and epidural spinal stimulation (ESS) to define how these approaches determine the ability to maintain self-assisted standing after SCI.

Spinal circuitries below a paralyzing injury have a functional potential that far exceeds what has been thought possible. It has been demonstrated that task-specific motor therapy combined with epidural spinal cord stimulation (ESS) can promote improved motor function during postural, locomotor, and voluntary movement tasks, resulting in dramatic effects on the wellbeing of individuals with spinal cord injury (SCI). While these findings indicate a substantial promise for restoring mobility even after motor complete paralysis, chronic ESS is based on a high-cost implantable device, as well as an expensive and invasive surgical procedure. The investigators have developed a cost-effective alternative to ESS - non-invasive, transcutaneous electrical stimulation of the spinal cord (TSS). Preliminary works demonstrate that this neuromodulatory strategy provides sufficient specificity to selectively stimulate multisegmental dorsal nerve roots, enable stepping movements, and improve postural control during sitting and standing in individuals with motor complete SCI. The similarities between the effects of ESS and TSS are of critical importance in guiding more individually-specific neuromodulatory approaches to improve motor function and mobility after SCI, but have not been compared directly in the same subjects. This study is focused on investigation the effects and mechanisms of each spinal neuromodulation strategy in regaining self-assisted standing. Not only is the recovery of balance control one of the most desired goals of people with paralysis, it provides the foundation necessary for regaining the ability to walk, and is critical to future therapies, involving robotic (e.g. exoskeleton) technologies. The objectives of this study are (1) to define the therapeutic potential of TSS during standing in individuals with motor complete SCI, and (2) to identify the neurophysiological and functional signatures of TSS and ESS. The central hypothesis is that each of the neuromodulatory strategies, when individually tailored, can result in significant motor recovery in individuals with chronic paralysis by reactivation and integration of networks that were clinically dormant prior to the intervention. The investigators predict that this proposal will have a high impact given that it encompasses multiple functional systems that contribute to the independence and quality of life in a broad population of individuals with SCI, and provides the first direct comparison of the invasive and non-invasive approaches. The investigators propose a progressive, mechanistic, and translational study to validate the effects of each approach, examine the neuroplastic capacity caused by activity-based training in the presence of TSS, and evaluate TSS and ESS stimulation paradigms as rehabilitative modalities after SCI.