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).
Single-blind, randomized, sham-controlled, crossover study.
Medical research institute and rehabilitation hospital.
Volunteers (N=9) with chronic SCI and motor dysfunction in wrist extensor muscles.
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.
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.
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.
List of abbreviations:AIS (American Spinal Injury Association Impairment Scale), ANOVA (analysis of variance), a-tDCS (anodal transcranial direct current stimulation), CST (corticospinal tract), ECR (extensor carpi radialis), ES (electrical stimulation), MEP (motor-evoked potential), MSO (maximal stimulator output), MVC (maximum voluntary contraction), M1 (primary motor cortex), RMS (root-mean-square), rMT (resting motor threshold), SCI (spinal cord injury), tDCS (transcranial direct current stimulation), TMS (transcranial magnetic stimulation), UEMS (upper extremity motor score), VAS (visual analog scale)
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Published online: November 22, 2014
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.
© 2015 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.