title: A comparison of relative-frequency and threshold-hunting methods to determine stimulus intensity in transcranial magnetic stimulation.
abstract: OBJECTIVE
  Stimulation intensity (SI) in transcranial magnetic stimulation is commonly set in relation to motor threshold (MT), or to achieve a motor-evoked potential (MEP) of predefined amplitude (usually 1 mV). Recently, IFCN recommended adaptive threshold-hunting over the previously endorsed relative-frequency method. We compared the Rossini-Rothwell (R-R) relative-frequency method to an adaptive threshold-hunting method based on parameter estimation by sequential testing (PEST) for determining MT and the SI to target a MEP amplitude of 1 mV (I(1) mV).
  
  
  METHODS
  In 10 healthy controls we determined MT and I(1) mV with R-R and PEST using a blinded crossover design, and performed within-session serial PEST measurements of MT.
  
  
  RESULTS
  There was no significant difference between methods for MT (52.6±2.6% vs. 53.7±3.1%; p=0.302; % maximum stimulator output; R-R vs. PEST, respectively) or I(1) mV (66.7±3.0% vs. 68.8±3.8%; p=0.146). There was strong correlation between R-R and PEST estimates for both MT and I(1) mV. R-R required significantly more stimuli than PEST. Serial measurements of MT with PEST were reproducible.
  
  
  CONCLUSIONS
  PEST has the advantage of speed without sacrificing precision when compared to the R-R method, and is adaptable to other SI targets.
  
  
  CONCLUSIONS
  Our results in healthy controls add to increasing evidence in favour of adaptive threshold-hunting methods for determining SI.
authors.affiliation: Australian Neuro-Muscular Research Institute and Centre for Neuromuscular and Neurological Disorders, M518, University of Western Australia, Nedlands, WA 6009, Australia.
authors.forename: B I
authors.initials: BI
authors.lastname: Silbert
authors.forename: H I
authors.initials: HI
authors.lastname: Patterson
authors.forename: D D
authors.initials: DD
authors.lastname: Pevcic
authors.forename: K A
authors.initials: KA
authors.lastname: Windnagel
authors.forename: G W
authors.initials: GW
authors.lastname: Thickbroom
mesh_terms: D000293:Adolescent; D000328:Adult; D018592:Cross-Over Studies; D003627:Data Interpretation, Statistical; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult