title: Intra- and interindividual variability of motor responses to repetitive transcranial magnetic stimulation.
abstract: OBJECTIVE
  Repetitive transcranial magnetic stimulation (rTMS) can modify cortical excitability and is widely used for clinical and research purposes. We sought to determine the intra- and interindividual variability of its effects on motor cortex excitability, and whether repeated paired-pulses yield less variability than repeated single-pulses.
  
  
  METHODS
  We investigated rTMS over the left motor cortex of 6 healthy subjects and recorded motor evoked potentials (MEPs) from the right abductor digiti minimi muscle. Eighty single suprathreshold stimuli or conditioning-test pairs of stimuli were delivered at 2Hz frequency. The pairs consisted of a subthreshold pulse followed by a suprathreshold pulse after 2, 5 or 10ms. In each subject we studied all types of rTMS 5 times on separate days. Single suprathreshold pulses at 0.17Hz preceded rTMS for baseline determination.
  
  
  RESULTS
  The day-to-day variability of MEPs during either type of rTMS was small compared to the subject-to-subject variability. MEPs increased during all types of rTMS except for interstimulus interval (ISI) 2ms. Paired-pulses yielded less variability than single-pulse rTMS.
  
  
  CONCLUSIONS
  Motor responses to rTMS show a high interindividual, but a low intraindividual variability. Repeated paired-pulses yield less variability than repeated single-pulses.
authors.affiliation: Department of Clinical Neurophysiology, University of Goettingen, P.O. Box 3742, D-37070, Goettingen, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Sommer
authors.forename: T
authors.initials: T
authors.lastname: Wu
authors.forename: F
authors.initials: F
authors.lastname: Tergau
authors.forename: W
authors.initials: W
authors.lastname: Paulus
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D004558:Electric Stimulation; D019054:Evoked Potentials, Motor / Q000502:physiology*; D006801:Humans; D009044:Motor Cortex / Q000502:physiology*; D011712:Pyramidal Tracts / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation