Fast and standardized motor-hotspot determination with automated TMS mapping

Granö, I.; Kahilakoski, O.-P.; Laine, M.; Kirchhoff, M.; Ahola, O.; Soto, A. M.; Matsuda, R. H.; Nieminen, A. E.; Pieramico, G.; Sinisalo, H.; Rissanen, I.; Tommila, T.; Roine, T.; Souza, V. H.; Ilmoniemi, R. J.; Lioumis, P.; Mutanen, T. P.

doi:10.1101/2025.09.24.678288

bioRxiv · 10.1101/2025.09.24.678288

Fast and standardized motor-hotspot determination with automated TMS mapping

Granö, I.·Kahilakoski, O.-P.·Laine, M.·Kirchhoff, M.·Ahola, O.·Soto, A. M.·Matsuda, R. H.·Nieminen, A. E.·Pieramico, G.·Sinisalo, H.·Rissanen, I.·Tommila, T.·Roine, T.·Souza, V. H.·Ilmoniemi, R. J.·Lioumis, P.·Mutanen, T. P.

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Abstract

Determining the optimal stimulation target for motor responses (motor hotspot) and the required intensity for reliably eliciting said responses (motor threshold) are common procedures in transcranial magnetic stimulation (TMS) research and treatments. However, the procedures for determining them are user-dependent, slow, and lack standardization, leading to long stimulation sessions with potentially inadequate outcomes. Partially automated algorithms for determining the motor threshold have been developed, but the motor hotspot is still largely mapped by hand. Automating the hotspot mapping will accelerate the process and improve standardization and accuracy. We developed a fully automated algorithm for finding the motor hotspot with multi-locus TMS and Bayesian optimization. Tested online in five healthy participants, the algorithm located motor hotspots with (mean {+/-} 95% CI) 2.1 {+/-} 0.7 mm and 6 {+/-} 2{degrees} difference from the global best target with only (mean) 47 stimuli. This is a significant improvement from previous motor-mapping algorithms, which do not optimize for stimulation location and orientation simultaneously. This accurate, fast, and user-independent procedure paves the way for faster experimental processes and more streamlined clinical applications.

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Granö, I., Kahilakoski, O.-P., Laine, M., Kirchhoff, M., Ahola, O., Soto, A. M., Matsuda, R. H., Nieminen, A. E., Pieramico, G., Sinisalo, H., Rissanen, I., Tommila, T., Roine, T., Souza, V. H., Ilmoniemi, R. J., Lioumis, P., Mutanen, T. P.. 2025-09-25. Fast and standardized motor-hotspot determination with automated TMS mapping. https://doi.org/10.1101/2025.09.24.678288

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