NON-INVASIVE SPINAL CORD STIMULATION FOR UPPER-LIMB IMPAIRMENTS: A MECHANISTIC STUDY IN UNINJURED- AND INJURED INDIVIDUALS

Recovery of arm and hand function following stroke or spinal cord injury (SCI) remains a key priority for those affected and a major challenge in neurorehabilitation. Cervical transcutaneous spinal cord stimulation (tSCS) has demonstrated promising therapeutic effects for improving upper-limb function after SCI, yet its underlying mechanisms remain unclear. Here, we sought to gain insights into the neural processes engaged by cervical tSCS through an ongoing clinical study investigating different stimulation configurations in able-bodied participants and individuals with stroke or SCI (NCT07334977).
Electrophysiological data were collected from fourteen able-bodied participants, one individual with stroke and one individual with cervical SCI. Each experimental session consisted of the administration of monophasic tSCS paired pulses delivered every 5 s at an inter-pulse interval of 50 ms and increasing stimulation amplitude, with the cathode placed at the C5/C6 or C7/T1 vertebrae and the anodes placed bilaterally at one of the following locations: medial, lateral, middle clavicles, or iliac crests. Evoked responses peak-to-peak amplitudes were measured from bilateral upper-limb muscles to obtain muscle- and condition-specific recruitment and post-activation depression (PAD) curves, and response thresholds.
Differences in response thresholds, recruitment curves, and PAD curves between the various conditions were consistently observed across participants. Anodes placed over the middle clavicles were associated with the overall lowest response thresholds, while those placed medially resulted in largest-amplitude responses and depression. Other stimulation parameters such as pulse width and cathode position also influenced these electrophysiological outcomes. Future work will investigate the correlation between these electrophysiological results and cervicothoracic neuroimaging data.