Non-invasive cervical electrical stimulation for SCI
1Wu Y, 2Santiago T, 2Saeed S, 2LiMonta J, 2Yung L, 3Kastuar S, 2Hussain J, 2Guber K, 4Weir J, 5Carmel J, 1Harel N
1James J. Peters VAMC, Icahn School of Medicine at Mount Sinai, Bronx, NY, USA; 2James J. Peters VAMC, Bronx, NY, USA; 3Icahn School of Medicine at Mount Sinai, New York, NY, USA; 4University of Kansas, Lawrence, KS, USA; 5Burke Medical Research Institute, White Plains, NY, USA
Objective: Spinal cord injury (SCI) results in a mixture of damaged and spared neural circuits. Activating spared nerve circuits augments neural plasticity. Paired stimulation between different sites of the nervous system may lead to more efficient strengthening of distinct synaptic targets than unpaired stimulation. With this goal in mind, we aim to use a novel method of non-invasive cervical electrical stimulation (CES). CES activates nerve roots across multiple myotomes in both upper extremities simultaneously. This method can be paired with transcranial magnetic stimulation, peripheral nerve stimulation, or volitional movement to both measure and attempt to strengthen circuit function. Methods: Transcutaneous stimulation is delivered via 5x10 cm electrodes, with the anode placed over the ~C4-C5 levels anteriorly and cathode over the ~T2-T4 levels posteriorly. Preliminary experiments involved optimizing stimulus waveform and titrating intensity to selectively activate either sensory afferent or motor efferent nerve roots. Subsequent experiments tested the acute effects of CES pulses of varying intensities and timing on paired TMS evoked potentials. Ongoing experiments are investigating the effects of repetitive pulses of CES paired with either TMS or peripheral nerve stimulation; the effects of CES on concurrent volitional pinch or wrist movements; and mechanistic circuit interactions between CES, peripheral, and supraspinal pathways. Blood pressure, heart rate, oxygenation, and subjective tolerance is monitored at all times. Results: To date, 15 able-bodied volunteers and 8 incomplete cervical SCI subjects have undergone >150 CES sessions without major safety or tolerability issues. CES travels via sensory afferents at peri-threshold intensity, and directly through motor efferents at higher intensity. Subthreshold CES pulses facilitate evoked responses to TMS in timing-dependent fashion. Suprathreshold CES pulses induce a ‘spinal silent period’ during concurrent volitional movement. Other experiments are ongoing. Conclusion: Our novel approach to transcutaneous cervical electrical stimulation provides both mechanistic insight and potential therapeutic application toward strengthening spared synapses to upper extremity muscles after SCI. The ability of subthreshold CES to facilitate response to transcranial magnetic stimulation suggests that it may also be able to enhance response to physical rehabilitation by facilitating volitional movements. Support: New York State DOH C30599; New York State DOH C31291; Craig H. Neilsen Foundation 457648.
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