Article
Factors influencing corticospinal excitability measured with navigated transcranial magnetic stimulation (nTMS)
Einflussfaktoren auf kortikospinale Erregbarkeit gemessen mit transkranieller Magnetstimulation (TMS)
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Authors
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Melina Engelhardt
- Charité Universitätsmedizin, Klinik für Neurochirurgie, Berlin, Deutschland; Charité Universitätsmedizin, Einstein Center für Neurowissenschaften, Berlin, Deutschland
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Darko Komnenić
- Humboldt Universität Berlin, Berlin School of Mind and Brain, Berlin, Deutschland
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Fabia Roth
- Charité Universitätsmedizin, Klinik für Neurochirurgie, Berlin, Deutschland
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Leona Kawelke
- Charité Universitätsmedizin, Klinik für Neurochirurgie, Berlin, Deutschland
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Carsten Finke
- Charité Universitätsmedizin, Einstein Center für Neurowissenschaften, Berlin, Deutschland; Humboldt Universität Berlin, Berlin School of Mind and Brain, Berlin, Deutschland; Charité Universitätsmedizin, Klinik für Neurologie, Berlin, Deutschland
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Thomas Picht
- Charité Universitätsmedizin, Klinik für Neurochirurgie, Berlin, Deutschland; Charité Universitätsmedizin, Einstein Center für Neurowissenschaften, Berlin, Deutschland; Humboldt Universität Berlin, Cluster of Excellence “Matters of Activity. Image Space Material”, Berlin, Deutschland
| Published: | June 4, 2021 |
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Outline
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Objective: Navigated transcranial magnetic stimulation (nTMS) is increasingly used in neurosurgical preoperative diagnostics and explored as a therapy option. Most of these applications rely on the resting motor threshold (RMT), a measure of cortical excitability, to scale intensity of stimulation sequences and evaluate treatment outcomes. Consequently, accurate measurement of the RMT is crucial and understanding of its confounders needs to be improved. The aim of this study was to validate findings on the impact of coil-to-cortex distance (CCD), age, cortical grey matter volume, hemisphere and functional connectivity between motor areas on the RMT.
Methods: 35 healthy right-handed subjects (38.7 ± 13.7 years, 19 females) without any neurological or psychiatric condition were investigated using navigated TMS and their RMT was assessed. CCD, age, grey matter volume and resting-state functional connectivity between various motor areas were assessed. Additionally, the effect of the hemisphere was investigated. The effect of these predictors on the RMT was assessed with a linear mixed model to account for non-independence of observations within the same subjects.
Results: The RMT varied between 23 and 51% of stimulator output (mean 34.0%, standard deviation 6.1%). The model tested in this study explained 44% of variability in the RMT. CCD was positively associated with the RMT (b = 1.46, t(34)=5.51, p <.001) and we obtained strong evidence (BF10 = 1.8*104) for this effect. None of the other investigated factors influenced the RMT significantly. The absence of these effects was further moderately supported by Bayes Factors.
Conclusion: Our results are in line with previous studies showing an effect of CCD on the RMT. In contrast to our hypothesis, we did not see an impact of any of the other investigated factors. Thus, the variance explained by the model remained low. This highlights the need for a more through investigation of factors potentially influencing the RMT and contributing to changes in corticospinal excitability.
