Transcutaneous spinal cord stimulation (tSCS) is a promising non-invasive method to improve motor function in individuals with spinal cord injury (SCI) by enhancing spinal reflex pathways. This study aimed to investigate the effects of different tSCS electrode placement montages and targeted spinal levels on neurophysiological responses such as spinally evoked motor responses (sEMRs), dorsal root reflex activation, and muscle recruitment in individuals with SCI and healthy controls to optimize stimulation strategies for motor recovery. Five participants (three individuals with SCI and two controls) underwent transcutaneous spinal cord stimulation using various electrode montages, target spinal level stimulation, and single- and paired-pulse paradigms. Electromyographic responses were analyzed to determine sEMR threshold, amplitudes, and paired-pulse attenuation. Different spinal levels and spatial configurations of electrode placements influenced the sEMR threshold and incidence of sEMR across all participants. Paired-pulse analysis showed more pronounced second-pulse attenuation in SCI participants (48 ± 36%) than in controls (12 ± 20%, p = 0.0425), with distinct trends observed across montages and muscle groups. These findings suggest that spinal level, electrode configuration, and paired-pulse effects are key factors in personalizing tSCS, informing the development of patient-centered therapeutic strategies. Future studies with larger and more diverse cohorts are needed to validate and expand these findings.
Keywords: dorsal root reflex pathway; electrode placement montages; paired pulse; patient-centric; personalization; transcutaneous spinal cord stimulation (tSCS); upper extremity.