title: Corticospinal excitability is dependent on the parameters of peripheral electric stimulation: a preliminary study.
abstract: OBJECTIVE
  To evaluate the effect of 6 electric stimulation paradigms on corticospinal excitability.
  
  
  METHODS
  Using a same subject pre-post test design, transcranial magnetic stimulation (TMS) was used to measure the responsiveness of corticomotor pathway to biceps and triceps brachii muscles before and after 30 minutes of electric stimulation over the biceps brachii. Six different electric stimulation paradigms were applied in random order, at least 3 days apart.
  
  
  METHODS
  Motor control research laboratory.
  
  
  METHODS
  Healthy subjects (N=10; 5 women, 5 men; mean age ± SD, 26 ± 3.6y).
  
  
  METHODS
  Six different electric stimulation paradigms with varied stimulus amplitude, frequency, and ramp settings.
  
  
  METHODS
  Amplitudes of TMS-induced motor evoked potentials at biceps and triceps brachii normalized to maximal M-wave amplitudes.
  
  
  RESULTS
  Electric stimulation delivered at stimulus amplitude sufficient to evoke a sensory response at both 10 Hz and 100 Hz, and stimulus amplitude to create a noxious response at 10 Hz decreased corticomotor responsiveness (all P<0.01). Stimulation sufficient to induce a motor contraction (30 Hz) applied in a ramped pattern to mimic a voluntary activation increased corticomotor responsiveness (P=0.002), whereas constant low- and high-intensity motor stimulation at 10 Hz did not. Corticomotor excitability changes were similar for both the stimulated muscle and its antagonist.
  
  
  CONCLUSIONS
  Stimulus amplitude (intensity) and the nature (muscle flicker vs contraction) of motor stimulation have a significant impact on changes in corticospinal excitability induced by electric stimulation. Here, we demonstrate that peripheral electric stimulation at stimulus amplitude to create a sensory response reduces corticomotor responsiveness. Conversely, stimulus amplitude to create a motor response increases corticomotor responsiveness, but only the parameters that create a motor response that mimics a voluntary muscle contraction.
authors.affiliation: School of Health and Rehabilitation Sciences (Physiotherapy) and the National Health and Medical Research Council Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, University of Queensland, St Lucia, Brisbane, QLD, Australia. l.chipchase@uq.edu.au
authors.forename: Lucy S
authors.initials: LS
authors.lastname: Chipchase
authors.forename: Siobhan M
authors.initials: SM
authors.lastname: Schabrun
authors.forename: Paul W
authors.initials: PW
authors.lastname: Hodges
mesh_terms: D000328:Adult; D001132:Arm / Q000502:physiology*; D004599:Electric Stimulation Therapy / Q000379:methods*; D004576:Electromyography; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation