Motor threshold in transcranial magnetic stimulation: comparison of three estimation methods.
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.
Tranulis
C
C
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.
Guéguen
B
B
Pham-Scottez
A
A
Vacheron
M N
MN
Cabelguen
G
G
Costantini
A
A
Valero
G
G
Galinovski
A
A
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*