Combined neuromuscular electrical stimulation and transcutaneous spinal direct current stimulation increases motor cortical plasticity in healthy humans

Tadaki Koseki; Daisuke Kudo; Kaito Yoshida; Mitsuhiro Nito; Keita Takano; Masafumi Jin; Shigeo Tanabe; Toshiaki Sato; Hiroshi Katoh; Tomofumi Yamaguchi

doi:10.3389/fnins.2022.1034451

Combined neuromuscular electrical stimulation and transcutaneous spinal direct current stimulation increases motor cortical plasticity in healthy humans

Front Neurosci. 2023 Jan 13:16:1034451. doi: 10.3389/fnins.2022.1034451. eCollection 2022.

Authors

Affiliations

¹ Graduate School of Health Sciences, Yamagata Prefectural University of Health Sciences, Yamagata, Japan.
² Department of Physical Therapy, Yamagata Prefectural University of Health Sciences, Yamagata, Japan.
³ Department of Anatomy and Structural Science, Yamagata University School of Medicine, Yamagata, Japan.
⁴ Faculty of Rehabilitation, School of Health Sciences, Fujita Health University, Toyoake, Japan.
⁵ Department of Occupational Therapy, Yamagata Prefectural University of Health Sciences, Yamagata, Japan.
⁶ Department of Physical Therapy, Faculty of Health Science, Juntendo University, Tokyo, Japan.

Abstract

Introduction: Neuromuscular electrical stimulation (NMES) induces neural plasticity of the central nervous system (CNS) and improves motor function in patients with CNS lesions. However, the extended stimulus duration of NMES reduces its clinical applicability. Transcutaneous spinal direct current stimulation (tsDCS), which increases afferent input, may enhance the effects and reduce the stimulus duration of NMES. This study investigated the excitability of the motor cortex, somatosensory cortex, and spinal motor neurons after the combined stimulation of NMES and tsDCS.

Methods: Among the 55 participants in this study, 24 were allocated to experiment 1, 15 to experiment 2, and 16 to experiment 3. They received intervention for 20 min on different days: (1) NMES combined with tsDCS (NMES + tsDCS), (2) NMES combined with sham tsDCS (NMES + sham tsDCS), and (3) sham NMES combined with tsDCS (sham NMES + tsDCS). NMES was delivered to the right common peroneal nerve at 25 Hz with the intensity at 120% of the motor threshold. For tsDCS, the cathodal electrode was positioned on the thoracic 10th-12th vertebral levels, and the anodal electrode was located on the right shoulder. The stimulus intensity was 2.5 mA. In experiment 1, motor evoked potentials (MEPs) and short-latency intracortical inhibition (SICI) were measured by transcranial magnetic stimulation up to 60 min after stimulation. The spinal motor neurons' excitability was assessed by recording the posterior root muscle reflex (PRMR) induced via transcutaneous spinal cord stimulation in experiment 2, and the primary somatosensory cortex excitability was evaluated by recording the somatosensory evoked potentials (SEPs) in experiment 3 up to 15 min after stimulation.

Results: Compared to before the stimulation, NMES + tsDCS significantly increased MEP for 60 min or more, and significantly decreased SICI immediately after. Conversely contrast, the PRMR significantly decreased immediately after, and SEPs were unchanged.

Discussion: These results suggest that simultaneous afferent inputs from different stimulus positions critically induce primary motor cortex plasticity. The combined stimulation of NMES with tsDCS may facilitate the development of a new neurorehabilitation technique.

Keywords: afferent input; corticospinal projection; motor cortical excitability; neural plasticity; spinal excitability.

Grants and funding

Partial financial support was received from the Funds for a Grant-in-Aid for Young Scientists (18K17723) to TY.