title: Inverse correlation between resting motor threshold and corticomotor excitability after static magnetic stimulation of human motor cortex.
abstract: BACKGROUND
  High-strength static magnetic field stimulation (SMS) results in a period of reduced corticomotor excitability that may be mediated through a decrease in membrane excitability.
  
  
  OBJECTIVE
  As resting motor threshold (RMT) is thought to reflect membrane excitability, we hypothesized that SMS may increase RMT and that there would be an inverse relationship between RMT and motor-evoked potential (MEP) amplitude.
  
  
  METHODS
  Ten healthy subjects (aged 20-29; 4 females) participated in a double-blinded crossover design comparing MEP amplitude and RMT before and after a 15-min period of SMS or sham stimulation over primary motor cortex (M1).
  
  
  RESULTS
  MEP amplitude was initially significantly reduced post-SMS (∼20%), and returned to baseline by 6 min post-intervention. MEP amplitude and RMT were inversely correlated (r(2) = 0.924; P = 0.001). Sham stimulation had no effect on MEP amplitude (P = 0.969) or RMT (P = 0.549).
  
  
  CONCLUSIONS
  After SMS, corticomotor excitability is transiently reduced in association with a correlated modulation of RMT. SMS after effects may be mediated in part by a reduction in membrane excitability, suggesting a possible role for non-synaptic (intrinsic) plasticity mechanisms.
authors.affiliation: Centre for Neuromuscular and Neurological Disorders, University of Western Australia, Australian Neuro-Muscular Research Institute, M518, Nedlands, WA 6009, Australia.
authors.forename: Benjamin I
authors.initials: BI
authors.lastname: Silbert
authors.forename: David D
authors.initials: DD
authors.lastname: Pevcic
authors.forename: Heather I
authors.initials: HI
authors.lastname: Patterson
authors.forename: Kelly A
authors.initials: KA
authors.lastname: Windnagel
authors.forename: Gary W
authors.initials: GW
authors.lastname: Thickbroom
mesh_terms: D000328:Adult; D018592:Cross-Over Studies; D004311:Double-Blind Method; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D012146:Rest / Q000502:physiology; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
keywords: Motor threshold; PEST; Static magnetic stimulation; Transcranial magnetic stimulation