Estimating Resting Motor Thresholds in Transcranial Magnetic Stimulation Research and Practice: A computer Simulation Evaluation of Best Methods

Objectives: Resting motor threshold is the basic unit of dosing in transcranial magnetic stimulation (TMS) research and practice. There is little consensus on how best to estimate resting motor threshold with TMS, and only a few tools and resources are readily available to TMS researchers. The current study investigates the accuracy and efficiency of 5 different approaches to motor threshold assessment for TMS research and practice applications. Methods: Computer simulation models are used to test the efficiency and accuracy of 5 different adaptive parameter estimation by sequential testing (PEST) procedures. For each approach, data are presented with respect to the mean number of TMS trials necessary to reach the motor threshold estimate as well as the mean accuracy of the estimates. Results: A simple nonparametric PEST procedure appears to provide the most accurate motor threshold estimates, but takes slightly longer (on average, 3.48 trials) to complete than a popular parametric alternative (maximum likelihood PEST). Recommendations are made for the best starting values for each of the approaches to maximize both efficiency and accuracy. Conclusions: In light of the computer simulation data provided in this article, the authors review and suggest which techniques might best fit different TMS research and clinical situations. Lastly, a free user-friendly software package is described and made available on the world wide web that allows users to run all of the motor threshold estimation procedures discussed in this article for clinical and research applications.

[1]  P. Rossini,et al.  Magnetic stimulation: motor evoked potentials. The International Federation of Clinical Neurophysiology. , 1999, Electroencephalography and clinical neurophysiology. Supplement.

[2]  P. Rossini,et al.  Non-invasive electrical and magnetic stimulation of the brain, spinal cord and roots: basic principles and procedures for routine clinical application. Report of an IFCN committee. , 1994, Electroencephalography and clinical neurophysiology.

[3]  A Pentland,et al.  Maximum likelihood estimation: The best PEST , 1980, Perception & psychophysics.

[4]  K. Mills,et al.  Corticomotor threshold to magnetic stimulation: Normal values and repeatability , 1997, Muscle & nerve.

[5]  J Valls-Solé,et al.  Safety of rapid-rate transcranial magnetic stimulation in normal volunteers. , 1993, Electroencephalography and clinical neurophysiology.

[6]  F. Awiszus.  TMS and threshold hunting. , 2003, Supplements to Clinical neurophysiology.

[7]  Z. Nahas,et al.  Motor threshold in transcranial magnetic stimulation: a comparison of a neurophysiological method and a visualization of movement method. , 1998, The journal of ECT.

[8]  M. M. Taylor,et al.  PEST: Efficient Estimates on Probability Functions , 1967 .

[9]  E. Wassermann.  Variation in the response to transcranial magnetic brain stimulation in the general population , 2002, Clinical Neurophysiology.

[10]  Jejo D. Koola,et al.  The Maximum-likelihood Strategy for Determining Transcranial Magnetic Stimulation Motor Threshold, Using Parameter Estimation by Sequential Testing Is Faster Than Conventional Methods With Similar Precision , 2004, The journal of ECT.

[11]  E. Wassermann.  Risk and safety of repetitive transcranial magnetic stimulation: report and suggested guidelines from the International Workshop on the Safety of Repetitive Transcranial Magnetic Stimulation, June 5-7, 1996. , 1998, Electroencephalography and clinical neurophysiology.