Multi-locus transcranial magnetic stimulation system for electronically targeted brain stimulation

Nieminen, J. O.; Sinisalo, H.; Souza, V. H.; Malmi, M.; Yuryev, M.; Tervo, A. E.; Stenroos, M.; Milardovich, D.; Korhonen, J. T.; Koponen, L. M.; Ilmoniemi, R. J.

doi:10.1101/2021.09.20.461045

bioRxiv · 10.1101/2021.09.20.461045

Multi-locus transcranial magnetic stimulation system for electronically targeted brain stimulation

Nieminen, J. O.·Sinisalo, H.·Souza, V. H.·Malmi, M.·Yuryev, M.·Tervo, A. E.·Stenroos, M.·Milardovich, D.·Korhonen, J. T.·Koponen, L. M.·Ilmoniemi, R. J.

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Abstract

BackgroundTranscranial magnetic stimulation (TMS) allows non-invasive stimulation of the cortex. In multi-locus TMS (mTMS), the stimulating electric field (E-field) is controlled electronically without coil movement by adjusting currents in the coils of a transducer. ObjectiveTo develop an mTMS system that allows adjusting the location and orientation of the E-field maximum within a cortical region. MethodsWe designed and manufactured a planar 5-coil mTMS transducer to allow controlling the maximum of the induced E-field within a cortical region approximately 30 mm in diameter. We developed electronics with a design consisting of independently controlled H-bridge circuits to drive up to six TMS coils. To control the hardware, we programmed software that runs on a field-programmable gate array and a computer. To induce the desired E-field in the cortex, we developed an optimization method to calculate the currents needed in the coils. We characterized the mTMS system and conducted a proof-of-concept motor-mapping experiment on a healthy volunteer. In the motor mapping, we kept the transducer placement fixed while electronically shifting the E-field maximum on the precentral gyrus and measuring electromyography from the contralateral hand. ResultsThe transducer consists of an oval coil, two figure-of-eight coils, and two four-leaf-clover coils stacked on top of each other. The technical characterization indicated that the mTMS system performs as designed. The measured motor evoked potential amplitudes varied consistently as a function of the location of the E-field maximum. ConclusionThe developed mTMS system enables electronically targeted brain stimulation within a cortical region.

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Nieminen, J. O., Sinisalo, H., Souza, V. H., Malmi, M., Yuryev, M., Tervo, A. E., Stenroos, M., Milardovich, D., Korhonen, J. T., Koponen, L. M., Ilmoniemi, R. J.. 2021-09-23. Multi-locus transcranial magnetic stimulation system for electronically targeted brain stimulation. https://doi.org/10.1101/2021.09.20.461045

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