Original research
Intensity Dependent Effects of Transcranial Direct Current Stimulation on Corticospinal Excitability in Chronic Spinal Cord Injury

Presented as a poster to the American Society of Neurorehabilitation, May 20–23, 2013, San Diego, CA; and the International Congress of Clinical Neurophysiology, March 20–23, 2014 Berlin, Germany.
https://doi.org/10.1016/j.apmr.2014.11.004Get rights and content

Abstract

Objective

To investigate the effects of anodal transcranial direct current stimulation (a-tDCS) intensity on corticospinal excitability and affected muscle activation in individuals with chronic spinal cord injury (SCI).

Design

Single-blind, randomized, sham-controlled, crossover study.

Setting

Medical research institute and rehabilitation hospital.

Participants

Volunteers (N=9) with chronic SCI and motor dysfunction in wrist extensor muscles.

Interventions

Three single session exposures to 20 minutes of a-tDCS (anode over the extensor carpi radialis [ECR] muscle representation on the left primary motor cortex, cathode over the right supraorbital area) using 1mA, 2mA, or sham stimulation, delivered at rest, with at least 1 week between sessions.

Main Outcome Measures

Corticospinal excitability was assessed with motor-evoked potentials (MEPs) from the ECR muscle using surface electromyography after transcranial magnetic stimulation. Changes in spinal excitability, sensory threshold, and muscle strength were also investigated.

Results

Mean MEP amplitude significantly increased by approximately 40% immediately after 2mA a-tDCS (pre: 0.36±0.1mV; post: 0.47±0.11mV; P=.001), but not with 1mA or sham. Maximal voluntary contraction measures remained unaltered across all conditions. Sensory threshold significantly decreased over time after 1mA (P=.002) and 2mA (P=.039) a-tDCS and did not change with sham. F-wave persistence showed a nonsignificant trend for increase (pre: 32%±12%; post: 41%±10%; follow-up: 46%±12%) after 2mA stimulation. No adverse effects were reported with any of the experimental conditions.

Conclusions

The a-tDCS can transiently raise corticospinal excitability to affected muscles in patients with chronic SCI after 2mA stimulation. Sensory perception can improve with both 1 and 2mA stimulation. This study gives support to the safe and effective use of a-tDCS using small electrodes in patients with SCI and highlights the importance of stimulation intensity.

Section snippets

Participants and study design

Nine volunteers with SCI (5 men, 4 women; age range, 20–56y) participated in the study. Individuals were recruited if they fulfilled the following criteria: traumatic SCI at the cervical level (C4-7); some degree of motor function in wrist extension scoring 1 to 4 out of 5 on the Medical Research Council Scale for motor strength in the right extensor carpi radialis (ECR) muscle; a chronic injury (>8mo after injury); and tolerance to sitting upright for at least 1 hour. Individuals were excluded

Participant clinical characteristics: baseline data

Nine participants with SCI (5 men, 4 women; 40.8±14.2y; range, 20–56y) with motor complete or incomplete (5 AIS grade B, 4 AIS grade C) chronic traumatic lesions at the cervical level (C4-6) completed the study (Table 1). All but 1 participant was right-handed prior to injury, and the average time since injury was 5.9±2.9 years (range, 0.75–10.5y).

All participants had severe upper-limb impairment, with lack of motor control in the forearm muscles. The UEMS graded 5 muscles from 0 (total

Discussion

The observed transient improvements in the human motor and sensory systems after a-tDCS for 20 minutes supports the application of a-tDCS in individuals after chronic SCI. The magnitude of change in corticospinal excitability appeared to be intensity dependent, and improvements in sensory perception were more sensitive. These findings lend support to the theory that muscles with reduced motor output can demonstrate an a-tDCS–related improvement in corticospinal activation, regardless of the

Conclusions

The findings of the present study demonstrate for the first time, to our knowledge, that a 20-minute single session of a-tDCS leads to increases in corticospinal excitability for individuals with chronic SCI. Not only does a-tDCS modulate activity in the motor system, but changes in the sensory systems also occur. The magnitude of these changes may be intensity dependent; however, future studies should not rule out the potential of stimulation strength, duration, or frequency of sessions when

Suppliers

  • a.

    Neuroelectrics.

  • b.

    Biometrics Ltd.

  • c.

    Cambridge Electronic Design Ltd.

  • d.

    MagVenture Tonika Elektronik.

  • e.

    Digitimer Ltd.

  • f.

    IBM Corp.

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    • Cited by (0)

    Supported by the National Institutes of Health (grant nos. R01HD069776 and R21HD077616).

    Disclosures: Ruffini is a cofounder of Neuroelectrics, a company that manufactures the transcranial direct current stimulation technology used in the study. Pascual-Leone has a financial involvement with Neuroelectrics. The other authors have nothing to disclose.

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    Copyright © 2015 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.