Non-invasive spinal cord stimulation approaches and effects on motor pathways in humans

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Date
2023-08-21
Authors
Vasaghi, Attiyeh
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Abstract

Spinal cord injury (SCI) is a central nervous system injury that can lead to motor, sensory and autonomic dysfunction. Electrical stimulation of the spinal cord has been increasingly recognized as a method to facilitate motor function after SCI. Two types of non-invasive stimulation have been used, including transcutaneous electrical pulsed stimulation (EPS) and direct current stimulation (DCS). Although DCS and EPS increased excitability of spinal motorneurons, these types of stimulation have never been directly compared in terms of effects when applied in the same person. Moreover, effects of EPS and DCS on spinal networks were assessed near the site of stimulation. Therefore, we sought to compare effects of EPS and DCS when applied in the same person; and to determine effects of lumbar stimulation on excitability of motorneurons innervating forearm muscles. Participants with SCI and an intact spinal cord were recruited. Spinal electrical stimulation was applied over the T11-L1 vertebrae for 15 minutes during sham EPS, EPS, sham DCS, and DCS. Input-output curves of H-reflexes and motor-evoked potentials (MEP) induced by transcranial magnetic stimulation in the flexor carpi radialis (FCR) muscle were recorded before and after spinal stimulation. Inter-session analysis demonstrated a trend for decreasing H-reflex in the SCI group and for increasing MEP in both the SCI and intact groups following the DCS intervention. Our results demonstrated no significant changes in the excitability of spinal motorneurons or the corticospinal pathway after 15 minutes of EPS and DCS. Within-session analysis revealed a significant increase in the mean FCR H-reflex: after sham EPS in SCI group and after EPS and sham DCS in the intact group but these results were not confirmed by another standard H-reflex analysis. Additionally, in the SCI group after DCS, systolic blood pressure (BP) increased and heart rate (HR) decreased by 15.7% and by 8.6% pre-DCS values, respectively. Overall, increased BP and HR and the lack of excitability changes after DCS and EPS should be interpreted with caution due low number of participants and variable injury levels in the SCI group.

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Spinal cord injury, Stimulation, Neuromodulators
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