Non-Invasive Neuromodulation for Upper Extremity Function in Spinal Cord Injury: A Crossover Trial

Cervical transcutaneous spinal cord stimulation will be delivered following previously reported guidelines. Circular (1.25") electrodes will be placed over the cervical spinal cord between the C3 and C4 vertebral level, with rectangular return electrodes placed either over the clavicles or iliac crests. Biphasic stimulation will be delivered continuously at 30Hz, with a 1ms pulse width, and overlapping 10kHz carrier frequency (Gelenitis et al 2024; Moritz et al 2024). Stimulation will be delivered at a current intensity below motor threshold, that is below the intensity required to elicit a muscle twitch. Cervical tSCS will be delivered for at least 60 minutes during each training session, and FTP will occur during the active stimulation.

Paired transcranial magnetic stimulation and nerve stimulation will be implemented following a previously-published protocol for individuals with SCI (Jo et al 2023). Two figure-eight coils will be used to deliver bilateral magnetic stimulation of the motor cortex and will be combined with synchronous electrical stimulation of the brachial plexus and ulnar nerves, bilaterally. The timing of stimuli will be determined to ensure that electrical volleys arrive at the corticospinal motoneuronal synapse at an appropriate interval to induce long term potentiation. During each session, 360 paired stimuli will be delivered at a frequency of 0.2 Hz. The stimulation paradigm should take approximately 30 minutes. Following this, participants will then complete 60 minutes of FTP.

A typical rehabilitation program will be defined and delivered in consultation with physical and occupational therapists. The program will consist of functional tasks including repetitive activities of gross upper extremity movement, isolated finger movements, simple and complex pinch, and grasping activities. For each category, 4-10 activities with various difficulty levels will be identified. Each participant will perform at least 1-2 exercises within each category during each treatment session. Activities in each category will be chosen according to the participants' ability and adjusted based on the evolution of the ability to perform the functional task over time (graded training).