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bioRxiv · 10.1101/2021.08.24.457503

Trade-off between stimulation focality and the number of coils in multi-locus transcranial magnetic stimulation

Nurmi, S.·Karttunen, J.·Souza, V. H.·Ilmoniemi, R. J.·Nieminen, J. O.
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Abstract

ObjectiveCoils designed for transcranial magnetic stimulation (TMS) must incorporate trade-offs between the required electrical power or energy, focality and depth penetration of the induced electric field (E-field), coil size, and mechanical properties of the coil, as all of them cannot be optimally met at the same time. In multi-locus TMS (mTMS), a transducer consisting of several coils allows electronically targeted stimulation of the cortex without physically moving a coil. In this study, we aimed to investigate the relationship between the number of coils in an mTMS transducer, the focality of the induced E-field, and the extent of the cortical region within which the location and orientation of the maximum of the induced E-field can be controlled. ApproachWe applied convex optimization to design planar and spherically curved mTMS transducers of different E-field focalities and analyzed their properties. We characterized the trade-off between the focality of the induced E-field and the extent of the cortical region that can be stimulated with an mTMS transducer with a given number of coils. Main resultsAt the expense of the E-field focality, one can, with the same number of coils, design an mTMS transducer that can control the location and orientation of the peak of the induced E-field within a wider cortical region. SignificanceWith E-fields of moderate focality, the problem of electronically targeted TMS becomes considerably easier compared with highly focal E-fields; this may speed up the development of mTMS and the emergence of new clinical and research applications.

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Nurmi, S., Karttunen, J., Souza, V. H., Ilmoniemi, R. J., Nieminen, J. O.. 2021-08-25. Trade-off between stimulation focality and the number of coils in multi-locus transcranial magnetic stimulation. https://doi.org/10.1101/2021.08.24.457503

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