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 journalArticleScientificpeer-review

27 Citations (Scopus)
108 Downloads (Pure)


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
Issue number1
Publication statusPublished - 1 Jan 2022
MoE publication typeA1 Journal article-refereed


  • Coil
  • Electric field
  • Motor mapping
  • mTMS
  • Multi-locus
  • Transcranial magnetic stimulation
  • Transducer


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