Spinal Cord Stimulation for Functional Recovery in Humans With Tetraplegia

Current studies demonstrate that electrical spinal stimulation, either invasive or noninvasive, can play an important role in rehabilitation strategies aimed at improving limb function in humans with SCI (Taccola et al., 2018). Among current stimulation strategies, one of the most promising candidates to emerge in recent years is transcutaneous electrical spinal stimulation (TESS). TESS is a noninvasive technique that can be tailored to the needs of each individual, where several segments of the spinal cord can be stimulated at the same time, and delivery can be programed to interact with a rehabilitation strategy during functional movements, such as reaching or grasping. A key element to TESS is its ability to access spared spinal cord networks with minimal discomfort. Although promising, the knowledge of TESS remains limited in scope and more studies are needed to further identify its efficacy. In Aim 1, subjects will participate in two randomized sessions: 1) TESS, and 2) sham-TESS.\] In Aim 2, the investigators will examine the effect of stimulation and training for a total of 20 sessions (3 to 5 per week). Participants will be randomly assigned to: \[1) Closed-loop TESS applied during grasping + training, or 2) Closed-loop TESS applied during reaching + training.\] AIM 1 Subjects with SCI and without SCI (controls) will participate in two testing sessions, separated by 2-3 days, using a crossover design. In each session, TESS or sham-TESS will be applied over the cervical spinal cord. Functional and physiological measures will be acquired before and after each session. AIM 2 Develop methodologies to promote recovery of reaching and grasping movements. To accomplish this goal, the investigators will combine TESS applied in a closed-loop manner with massed practice upper-limb training. Participants will be assigned to one of three groups in a randomized order using a sham controlled design: \[1) Closed-loop TESS applied during grasping + training, 2) Closed-loop TESS applied during reaching + training, and 3) Closed-loop TESS applied during grasping \& reaching + training.\] TESS for 20-min will be followed by 60 min of massed practice exercise training (total=20 sessions).