A Review of Studies Comparing Methods for Determining Transcranial Magnetic Stimulation Motor Threshold: Observation of Movement or Electromyography Assisted

BACKGROUND: Early in the development of transcranial magnetic stimulation (TMS) as a research tool, scientists developed the concept of motor threshold (MT) as a method of quantifying dose and establishing safety. Neurophysiologists determined the MT with the aid of peripheral electromyography (EMG). More recently, clinicians started substituting the EMG with observed movements (OM) of the hand or digits. It is unclear whether the two approaches (EMG and OM) reach similar conclusions about an individual’s cortical excitability and when best to use each approach. OBJECTIVE: To review TMS studies directly comparing the EMG and OM MT methods. DESIGN: A systematic search of the literature on Medline from January 1995 through April 2008. RESULTS: Four articles directly compared the two approaches, reaching different and opposing findings. CONCLUSION S : The evidence supporting the substitution of EMG with OM is sparse and conflicting. Clinicians stimulating at or near safety guidelines should use the EMG method.