TMS motor thresholds correlate with TDCS electric field strengths in hand motor area
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Copyright © 2018 Mikkonen, Laakso, Sumiya, Koyama, Hirata and Tanaka. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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Date
2018-06-25
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Mcode
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Language
en
Pages
10
Series
Frontiers in Neuroscience, Volume 12, issue JUN
Abstract
Transcranial direct current stimulation (TDCS) modulates cortical activity and influences motor and cognitive functions in both healthy and clinical populations. However, there is large inter-individual variability in the responses to TDCS. Computational studies have suggested that inter-individual differences in cranial and brain anatomy may contribute to this variability via creating varying electric fields in the brain. This implies that the electric fields or their strength and orientation should be considered and incorporated when selecting the TDCS dose. Unfortunately, electric field modeling is difficult to perform; thus, a more-robust and practical method of estimating the strength of TDCS electric fields for experimental use is required. As recent studies have revealed a relationship between the sensitivity to TMS and motor cortical TDCS after-effects, the aim of the present study was to investigate whether the resting motor threshold (RMT), a simple measure of transcranial magnetic stimulation (TMS) sensitivity, would be useful for estimating TDCS electric field strengths in the hand area of primary motor cortex (M1). To achieve this, we measured the RMT in 28 subjects. We also obtained magnetic resonance images from each subject to build individual three-dimensional anatomic models, which were used in solving the TDCS and TMS electric fields using the finite element method (FEM). Then, we calculated the correlation between the measured RMT and the modeled TDCS electric fields. We found that the RMT correlated with the TDCS electric fields in hand M1 (R2 = 0.58), but no obvious correlations were identified in regions outside M1. The found correlation was mainly due to a correlation between the TDCS and TMS electric fields, both of which were affected by individual's anatomic features. In conclusion, the RMT could provide a useful tool for estimating cortical electric fields for motor cortical TDCS.Description
Keywords
Electric field estimation, FEM, Resting motor threshold, TDCS, TMS
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Citation
Mikkonen, M, Laakso, I, Sumiya, M, Koyama, S, Hirata, A & Tanaka, S 2018, ' TMS motor thresholds correlate with TDCS electric field strengths in hand motor area ', Frontiers in Neuroscience, vol. 12, no. JUN, 426 . https://doi.org/10.3389/fnins.2018.00426