title: Motor threshold in transcranial magnetic stimulation: comparison of three estimation methods.
abstract: OBJECTIVE
  Motor threshold (MT) is an important parameter for the practice of transcranial magnetic stimulation. Our goal was to compare three methods to estimate MT in a clinical setting.
  
  
  METHODS
  Comparison of three MT estimation algorithms: 1) the Rossini-Rothwell method consists in lowering stimulus intensity until only five positive responses out of 10 trials are recorded, defining MT; 2) the Mills-Nithi method considers the MT as the mean of an upper threshold (10 positive out of 10 trials) and a lower threshold (0 out of 10 trials); 3) the supervised parametric method estimates the MT by fitting (mathematically and graphically) a sigmoid function on raw data obtained by stimulation at variable intensities. Six MT estimations (two per method) were recorded in a single session in 10 healthy subjects.
  
  
  RESULTS
  The within-subject variation of MT (expressed as % of the mean MT+/-standard deviation) during a single session was of 8.5+/-7.2% for the Rossini-Rothwell method, 8.7+/-5.7% for the Mills-Nithi method and 9.5+/-4.0% for the supervised parametric method. No significant differences in variability of MT estimation were found between the methods, but the Rossini-Rothwell method was significantly shorter (half the number of stimuli compared to the two other methods).
  
  
  CONCLUSIONS
  In our setting, Rossini-Rothwell method was superior to the two other methods. The variability of MT estimation measured in our study is important, yet acceptable for clinical applications. However, this variability can be a source of considerable errors in excitability studies and should be a focus of future research.
authors.affiliation: Service Hospitalo-Universitaire de Santé Mentale et de Thérapeutique Pr H. Loo, Pr J.P. Olié, Centre Hospitalière Sainte-Anne, 1, rue Cabanis, Paris 75014, France.
authors.forename: C
authors.initials: C
authors.lastname: Tranulis
authors.forename: B
authors.initials: B
authors.lastname: Guéguen
authors.forename: A
authors.initials: A
authors.lastname: Pham-Scottez
authors.forename: M N
authors.initials: MN
authors.lastname: Vacheron
authors.forename: G
authors.initials: G
authors.lastname: Cabelguen
authors.forename: A
authors.initials: A
authors.lastname: Costantini
authors.forename: G
authors.initials: G
authors.lastname: Valero
authors.forename: A
authors.initials: A
authors.lastname: Galinovski
mesh_terms: D000328:Adult; D000465:Algorithms; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D012684:Sensory Thresholds; D050781:Transcranial Magnetic Stimulation / Q000379:methods*