title: Intensity dependent effects of transcranial direct current stimulation on corticospinal excitability in chronic spinal cord injury.
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).
  
  
  METHODS
  Single-blind, randomized, sham-controlled, crossover study.
  
  
  METHODS
  Medical research institute and rehabilitation hospital.
  
  
  METHODS
  Volunteers (N = 9) with chronic SCI and motor dysfunction in wrist extensor muscles.
  
  
  METHODS
  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 1 mA, 2 mA, or sham stimulation, delivered at rest, with at least 1 week between sessions.
  
  
  METHODS
  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 ± 0.1 mV; post: 0.47 ± 0.11 mV; P = .001), but not with 1 mA 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 2 mA 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 2 mA stimulation. Sensory perception can improve with both 1 and 2 mA 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.
authors.affiliation: Non-invasive Brain Stimulation and Human Motor Control Laboratory, Burke Medical Research Institute, White Plains, NY; Physical Medicine and Rehabilitation Department, Rumailah Hospital, Hamad Medical Corporation, Doha, Qatar; School of Exercise and Health Sciences, Edith Cowan University, Joondalup, WA, Australia. Electronic address: LMurray@hmc.org.qa.
authors.forename: Lynda M
authors.initials: LM
authors.lastname: Murray
authors.affiliation: Non-invasive Brain Stimulation and Human Motor Control Laboratory, Burke Medical Research Institute, White Plains, NY; Neurology Department, Weill Cornell Medical College, Cornell University, New York, NY; Centre for Neuromuscular and Neurological Disorders, University of Western Australia, Nedlands, WA, Australia.
authors.forename: Dylan J
authors.initials: DJ
authors.lastname: Edwards
authors.affiliation: Starlab Barcelona SL, Barcelona, Spain.
authors.forename: Giulio
authors.initials: G
authors.lastname: Ruffini
authors.affiliation: Non-invasive Brain Stimulation and Human Motor Control Laboratory, Burke Medical Research Institute, White Plains, NY; Neurology Department, Weill Cornell Medical College, Cornell University, New York, NY.
authors.forename: Douglas
authors.initials: D
authors.lastname: Labar
authors.affiliation: Burke Rehabilitation Hospital, White Plains, NY.
authors.forename: Argyrios
authors.initials: A
authors.lastname: Stampas
authors.affiliation: Berenson-Allen Center for Noninvasive Brain Stimulation, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA.
authors.forename: Alvaro
authors.initials: A
authors.lastname: Pascual-Leone
authors.affiliation: Non-invasive Brain Stimulation and Human Motor Control Laboratory, Burke Medical Research Institute, White Plains, NY; Neurology Department, Weill Cornell Medical College, Cornell University, New York, NY; Department of Neurology, University of Barcelona, Barcelona, Spain.
authors.forename: Mar
authors.initials: M
authors.lastname: Cortes
mesh_terms: D000328:Adult; D002908:Chronic Disease; D018592:Cross-Over Studies; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology; D026741:Physical Therapy Modalities; D011712:Pyramidal Tracts / Q000503:physiopathology*; D016037:Single-Blind Method; D013119:Spinal Cord Injuries / Q000534:rehabilitation*; D065908:Transcranial Direct Current Stimulation / Q000009:adverse effects / Q000379:methods*; D050781:Transcranial Magnetic Stimulation / Q000379:methods; D014953:Wrist / Q000503:physiopathology
keywords: Anodal stimulation transcranial direct current stimulation; Rehabilitation; Spinal cord injuries; Upper extremity