Transcutaneous spinal direct current stimulation (tsDCS) is a mild, non-invasive approach to increase spinal excitation and modulate spinal reflexes. Although ample evidence suggests tsDCS could enhance the effect of locomotor rehabilitation, the efficacy of this combinatorial strategy has not been investigated in individuals with ISCI. Based on supportive evidence from our prior feasibility study, the investigators will examine initial efficacy and mechanistic changes from combined tsDCS and locomotor training (tsDCS+LT).~Specific aim 1: To determine the effect size and variance of response to combined tsDCS and LT to enable power analysis for a larger clinical trial. Participants (chronic, motor ISCI) will complete a double-blind, randomized parallel-group design study to examine the effects of tsDCS (20 sessions, 30 minutes, anodal, 2.5 mA) delivered concurrently with LT. Walking outcomes will be measured pre- and post-intervention to compare the effects of tsDCS+LT versus sham+LT. Primary outcomes will be changes in overground walking speed and endurance.~Specific aim 2: To test the hypothesis that tsDCS+LT increases spinal motor excitability and reflex modulation. Spinal excitability will be assessed by Hoffman reflex amplitudes. Reflex modulation will be assessed by normalized measures of reflex post-activation depression as well as by gait phase-dependent modulation.~This proposed clinical trial will utilize a double-blind, randomized parallel-group experimental design. Once screening is complete, individuals will be enrolled for approximately two months to complete all study procedures. Participants will be randomized to receive either the higher or lower (sham) dose of tsDCS. The intervention will consist of 20 sessions (5 weeks x 4 sessions/week) of LT with the assigned tsDCS dose.~All participants will complete assessments at three time points. Clinical assessments to characterize injury severity and baseline characteristics, biomechanical, electromyographic (EMG) and clinical assessments of walking function, and reflex testing will be completed pre-intervention and one to three days post-intervention. A follow-up assessment consisting of clinical walking and mobility function outcomes only will be reassessed two weeks post-intervention.
Locomotor training (LT) facilitates recovery of spinal locomotor networks after incomplete spinal cord injury (ISCI), but walking impairments persist. A limitation of LT is insufficient excitation of spinal locomotor circuits to induce neuroplastic recovery. Transcutaneous spinal direct current stimulation (tsDCS) is a non-invasive approach to increase spinal excitation and modulate spinal reflexes. The study will examine if tsDCS combined with LT enhances locomotor rehabilitation after ISCI.