Comparison of figure-of-8 and circular coils for threshold tracking transcranial magnetic stimulation measurements

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Objectives: The transcranial magnetic stimulation (TMS) technique of threshold-tracking short-interval intracortical inhibition (T-SICI) has been proposed as a diagnostic tool for amyotrophic lateral sclerosis (ALS). Most of these studies have used a circular coil, whereas a figure-of-8 coil is usually recommended for paired-pulse TMS measurements. The aim of this study was to compare figure-of-8 and circular coils for T-SICI in the upper limb, with special attention to reproducibility, and the pain or discomfort experienced by the subjects. Methods: Twenty healthy subjects (aged: 45.5 ± 6.7, mean ± SD, 9 females, 11 males) underwent two examinations with each coil, in morning and afternoon sessions on the same day, with T-SICI measured at interstimulus intervals (ISIs) from 1−7 ms. After each examination the subjects rated degree of pain/discomfort from 0 to 10 using a numerical rating scale (NRS). Results: Mean T-SICI was higher for the figure-of-8 than for the circular coil at ISI of 2 ms (p < 0.05) but did not differ at other ISIs. Intra-subject variability did not differ between coils, but mean inhibition from 1−3.5 ms was less variable between subjects with the figure-of-8 coil (SD 7.2% vs. 11.2% RMT, p < 0.05), and no such recordings were without inhibition (vs. 6 with the circular coil). The subjects experienced less pain/discomfort with the figure-of-8 coil (mean NRS: 1.9 ± 1.28 vs 2.8 ± 1.60, p < 0.005). Discussion: The figure-of-8 coil may have better applicability in patients, due to the lower incidence of lack of inhibition in healthy subjects, and the lower experience of pain or discomfort.

TidsskriftNeurophysiologie Clinique
Udgave nummer2
Sider (fra-til)153-160
Antal sider8
StatusUdgivet - mar. 2021
Udgivet eksterntJa

Bibliografisk note

Funding Information:
The project received funding from the Lundbeck Foundation (grant R290-2018-751 ), the Aage & Johanne Louis-Hansens Foundation ( 18-2B-2454/L 445 ) , A.P. Møller and wife Chastine McKinney Møllers Foundation (grant ref. 17-L-0365 ) and the Independent Research Fund Denmark (grant ref. DFF 7025-00066 ). None of the funders had any role in the design, data collection, analysis or data interpretation, writing or publication decisions.

Publisher Copyright:
© 2021 Elsevier Masson SAS

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