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. 2023 Aug 26;13(9):1246.
doi: 10.3390/brainsci13091246.

Variability in Motor Threshold during Transcranial Magnetic Stimulation Treatment for Depression: Neurophysiological Implications

Alexis Bourla  1   2   3   4 , Stéphane Mouchabac  1   2 , Léonard Lorimy  4 , Bertrand Crette  4 , Bruno Millet  2   5 , Florian Ferreri  1   2
Affiliations

Variability in Motor Threshold during Transcranial Magnetic Stimulation Treatment for Depression: Neurophysiological Implications

Alexis Bourla et al. Brain Sci. .

Abstract

The measurement of the motor threshold (MT) is an important element in determining stimulation intensity during Transcranial Magnetic Stimulation treatment (rTMS). The current recommendations propose its realization at least once a week. The variability in this motor threshold is an important factor to consider as it could translate certain neurophysiological specificities. We conducted a retrospective naturalistic study on data from 30 patients treated for treatment-resistant depression in an rTMS-specialized center. For each patient, weekly motor-evoked potential (MEP) was performed and several clinical elements were collected as part of our clinical interviews. Regarding response to treatment (Patient Health Questionnaire-9 (PHQ-9) before and after treatment), there was a mean difference of -8.88 (-21 to 0) in PHQ9 in the Theta Burst group, of -9.00 (-18 to -1) in the High-Frequency (10 Hz) group, and of -4.66 (-10 to +2) in the Low-Frequency (1 Hz) group. The mean improvement in depressive symptoms was 47% (p < 0.001, effect-size: 1.60). The motor threshold changed over the course of the treatment, with a minimum individual range of 1 point and a maximum of 19 points (total subset), and a greater concentration in the remission group (4 to 10) than in the other groups (3 to 10 in the response group, 1 to 8 in the partial response group, 3 to 19 in the stagnation group). We also note that the difference between MT at week 1 and week 6 was statistically significant only in the remission group, with a different evolutionary profile showing an upward trend in MT. Our findings suggest a potential predictive value of MT changes during treatment, particularly an increase in MT in patients who achieve remission and a distinct "break" in MT around the 4th week, which could predict nonresponse.

Keywords: motor threshold; transcranial magnetic stimulation; treatment-resistant depression.

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Conflict of interest statement

A.B., S.M., L.L., B.C. and F.F. declare no conflict of interest related to the subject of this article. B.M. is an SYNEIKA (neuronavigation system applied to TMS) shareholder and has served as a consultant for Brainsway.

Figures

Figure 1
Figure 1
Motor-evoked potential. Red circle: peak-to-peak amplitude (µV), blue circle on the left: history of motor-evoked potential, purple circle: resting motor threshold target, blue circle on the right: stimulation intensity.
Figure 2
Figure 2
Evolution of MT over the 6-week treatment across different groups. (a) Mean MT for remission group, (b) Mean MT for responder group (including remitters), (c) Mean MT for responders group (excluding remitters), (d) Mean MT for partial responders group, (e) Mean MT for stagnation group.
Figure 3
Figure 3
MT variability over time.
See this image and copyright information in PMC

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