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Neurophysiol Clin. 2006 Jan-Feb;36(1):1-7. Epub 2006 Feb 2.

Motor threshold in transcranial magnetic stimulation: comparison of three estimation methods.

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1
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.

Abstract

AIMS:

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).

CONCLUSION:

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.

PMID:
16530137
DOI:
10.1016/j.neucli.2006.01.005
[Indexed for MEDLINE]
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