title: Occlusion of bidirectional plasticity by preceding low-frequency stimulation in the human motor cortex.
abstract: OBJECTIVE
  Low-frequency stimulation, which does not induce long-term potentiation (LTP) or long-term potentiation (LTD) by itself, suppresses consecutive LTP or LTD induction in vitro. We tested whether a similar interaction occurs in the human motor cortex.
  
  
  METHODS
  LTP- or LTD-like plasticity was induced using paired associative stimulation (PAS) with 25 and 10 ms interstimulus interval and conditioned by suprathreshold repetitive transcranial magnetic stimulation (rTMS) at a frequency of 0.1Hz.
  
  
  RESULTS
  RTMS completely abolished the significant increase of motor-evoked potential (MEP) amplitudes after PAS(25 ms) (PAS(25 ms) only: 1.05+/-0.14 to 1.76+/-0.66 mV, p=0.001; rTMS+PAS(25 ms): 1.08+/-0.18 to 1.02+/-0.44 mV, n.s.) and also abolished the significant decrease of MEP amplitudes after PAS(10 ms) (PAS(10 ms) only: 1.00+/-0.14 to 0.73+/-0.32 mV; rTMS+PAS(10 ms): 1.15+/-0.35 to 1.25+/-0.43 mV, p=0.006). RTMS alone did not significantly alter MEP amplitudes but increased SICI and LICI.
  
  
  CONCLUSIONS
  Low frequency stimulation increases intracortical inhibition and occludes LTP- and LTD-like plasticity in the human motor cortex.
  
  
  CONCLUSIONS
  This finding supports the concept that metaplasticity in the human motor cortex follows similar rules as metaplasticity in in vitro experiments.
authors.affiliation: Division of Neuropaediatrics and Muscular Disorders, Department of Paediatrics and Adolescent Medicine, University Hospital Freiburg, Freiburg, Germany.
authors.forename: Igor
authors.initials: I
authors.lastname: Delvendahl
authors.forename: Nikolai H
authors.initials: NH
authors.lastname: Jung
authors.forename: Florian
authors.initials: F
authors.lastname: Mainberger
authors.forename: Nicola G
authors.initials: NG
authors.lastname: Kuhnke
authors.forename: Matthias
authors.initials: M
authors.lastname: Cronjaeger
authors.forename: Volker
authors.initials: V
authors.lastname: Mall
mesh_terms: D000328:Adult; D001703:Biophysics; D013181:Cortical Spreading Depression / Q000502:physiology*; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology; D009044:Motor Cortex / Q000502:physiology*; D015999:Multivariate Analysis; D018482:Muscle, Skeletal / Q000294:innervation; D009433:Neural Inhibition / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation / Q000379:methods; D055815:Young Adult