A novel approach to localize cortical TMS effects

Konstantin Weise*, Ole Numssen, Axel Thielscher, Gesa Hartwigsen, Thomas R Knösche

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Abstract

Despite the widespread use of transcranial magnetic stimulation (TMS), the precise cortical locations underlying the resulting physiological and behavioral effects are still only coarsely known. To date, mapping strategies have relied on projection approaches (often termed "center of gravity" approaches) or maximum electric field value evaluation, and therefore localize the stimulated cortical site only approximately and indirectly. Focusing on the motor cortex, we present and validate a novel method to reliably determine the effectively stimulated cortical site at the individual subject level. The approach combines measurements of motor evoked potentials (MEPs) at different coil positions and orientations with numerical modeling of induced electric fields. We identify sharply bounded cortical areas, around the gyral crowns and rims of the motor hand area, as the origin of MEPs and show that the magnitude of the tangential component and the overall magnitude of the electric field are most relevant for the observed effect. To validate our approach, we identified the coil location and orientation that produces the maximal electric field at the predicted stimulation site, and then experimentally show that this location produces MEPs more efficiently than other tested locations/orientations. Moreover, we used extensive uncertainty and sensitivity analyses to verify the robustness of the method and identify the most critical model parameters. Our generic approach improves the localization of the cortical area effectively stimulated by TMS and may be transferred to other modalities such as language mapping.
Original languageEnglish
Article number116486
JournalNeuroImage
ISSN1053-8119
DOIs
Publication statusAccepted/In press - 2020

Cite this

Weise, K., Numssen, O., Thielscher, A., Hartwigsen, G., & Knösche, T. R. (Accepted/In press). A novel approach to localize cortical TMS effects. NeuroImage, [116486]. https://doi.org/10.1016/j.neuroimage.2019.116486
Weise, Konstantin ; Numssen, Ole ; Thielscher, Axel ; Hartwigsen, Gesa ; Knösche, Thomas R. / A novel approach to localize cortical TMS effects. In: NeuroImage. 2020.
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A novel approach to localize cortical TMS effects. / Weise, Konstantin; Numssen, Ole; Thielscher, Axel; Hartwigsen, Gesa; Knösche, Thomas R.

In: NeuroImage, 2020.

Research output: Contribution to journalJournal articleResearchpeer-review

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AU - Weise, Konstantin

AU - Numssen, Ole

AU - Thielscher, Axel

AU - Hartwigsen, Gesa

AU - Knösche, Thomas R

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AB - Despite the widespread use of transcranial magnetic stimulation (TMS), the precise cortical locations underlying the resulting physiological and behavioral effects are still only coarsely known. To date, mapping strategies have relied on projection approaches (often termed "center of gravity" approaches) or maximum electric field value evaluation, and therefore localize the stimulated cortical site only approximately and indirectly. Focusing on the motor cortex, we present and validate a novel method to reliably determine the effectively stimulated cortical site at the individual subject level. The approach combines measurements of motor evoked potentials (MEPs) at different coil positions and orientations with numerical modeling of induced electric fields. We identify sharply bounded cortical areas, around the gyral crowns and rims of the motor hand area, as the origin of MEPs and show that the magnitude of the tangential component and the overall magnitude of the electric field are most relevant for the observed effect. To validate our approach, we identified the coil location and orientation that produces the maximal electric field at the predicted stimulation site, and then experimentally show that this location produces MEPs more efficiently than other tested locations/orientations. Moreover, we used extensive uncertainty and sensitivity analyses to verify the robustness of the method and identify the most critical model parameters. Our generic approach improves the localization of the cortical area effectively stimulated by TMS and may be transferred to other modalities such as language mapping.

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