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

Jaakko O. Nieminen*, Heikki Sinisalo, Victor H. Souza, Mikko Malmi, Mikhail Yuryev, Aino E. Tervo, Matti Stenroos, Diego Milardovich, Juuso T. Korhonen, Lari M. Koponen, Risto J. Ilmoniemi

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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Abstract

Background: Transcranial 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.

Objective: To develop an mTMS system that allows adjusting the location and orientation of the E-field maximum within a cortical region.

Methods: We 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.

Results: The 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.

Conclusion: The developed mTMS system enables electronically targeted brain stimulation within a cortical region.
Original languageEnglish
Pages (from-to)116-124
Number of pages9
JournalBrain stimulation
Volume15
Issue number1
Early online date21 Nov 2021
DOIs
Publication statusPublished - Jan 2022

Bibliographical note

Funding Information:
This project has received funding from the Academy of Finland (decisions No. 294625, 306845, and 327326), the Finnish Cultural Foundation , the Instrumentarium Science Foundation , the Jane and Aatos Erkko Foundation , and the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 810377). The authors thank Matti Aho, Gustaf Järnefelt, Matti Mielonen, and Marko Ollikainen for useful discussions, Michael Serué for his work on the IGBT drivers, and Mikko Raskinen (Aalto University) and Tuomas Mutanen for the photos. The authors acknowledge the computational resources provided by the Aalto Science-IT project. The coil cables were donated by Nexstim Plc. Omnia helped with the bending of busbars for the pulse modules.

Funding Information:
This project has received funding from the Academy of Finland (decisions No. 294625, 306845, and 327326), the Finnish Cultural Foundation, the Instrumentarium Science Foundation, the Jane and Aatos Erkko Foundation, and the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 810377). The authors thank Matti Aho, Gustaf Järnefelt, Matti Mielonen, and Marko Ollikainen for useful discussions, Michael Serué for his work on the IGBT drivers, and Mikko Raskinen (Aalto University) and Tuomas Mutanen for the photos. The authors acknowledge the computational resources provided by the Aalto Science-IT project. The coil cables were donated by Nexstim Plc. Omnia helped with the bending of busbars for the pulse modules.

Publisher Copyright:
© 2021 The Author(s)

Keywords

  • Transcranial magnetic stimulation
  • mTMS
  • multi-locus
  • transducer
  • coil
  • electric field
  • motor mapping

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