Closed-loop optimization of transcranial magnetic stimulation with electroencephalography feedback

Aino E Tervo; Jaakko O Nieminen; Pantelis Lioumis; Johanna Metsomaa; Victor H Souza; Heikki Sinisalo; Matti Stenroos; Jukka Sarvas; Risto J Ilmoniemi

doi:10.1016/j.brs.2022.01.016

Closed-loop optimization of transcranial magnetic stimulation with electroencephalography feedback

Brain Stimul. 2022 Mar-Apr;15(2):523-531. doi: 10.1016/j.brs.2022.01.016. Epub 2022 Feb 14.

Authors

Aino E Tervo¹, Jaakko O Nieminen², Pantelis Lioumis³, Johanna Metsomaa⁴, Victor H Souza⁵, Heikki Sinisalo⁵, Matti Stenroos⁶, Jukka Sarvas⁶, Risto J Ilmoniemi⁵

Affiliations

¹ Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland; BioMag Laboratory, HUS Medical Imaging Center, University of Helsinki and Helsinki University Hospital, Helsinki, Finland; AMI Centre, Aalto NeuroImaging, Aalto University School of Science, Espoo, Finland.
² Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland; BioMag Laboratory, HUS Medical Imaging Center, University of Helsinki and Helsinki University Hospital, Helsinki, Finland. Electronic address: jaakko.nieminen@aalto.fi.
³ Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland; BioMag Laboratory, HUS Medical Imaging Center, University of Helsinki and Helsinki University Hospital, Helsinki, Finland; Cognitive Brain Research Unit, Department of Psychology and Logopedics, Faculty of Medicine, University of Helsinki, Helsinki, Finland.
⁴ Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland; Department of Neurology & Stroke and Hertie Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany.
⁵ Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland; BioMag Laboratory, HUS Medical Imaging Center, University of Helsinki and Helsinki University Hospital, Helsinki, Finland.
⁶ Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland.

Abstract

Background: Transcranial magnetic stimulation (TMS) is widely used in brain research and treatment of various brain dysfunctions. However, the optimal way to target stimulation and administer TMS therapies, for example, where and in which electric field direction the stimuli should be given, is yet to be determined.

Objective: To develop an automated closed-loop system for adjusting TMS parameters (in this work, the stimulus orientation) online based on TMS-evoked brain activity measured with electroencephalography (EEG).

Methods: We developed an automated closed-loop TMS-EEG set-up. In this set-up, the stimulus parameters are electronically adjusted with multi-locus TMS. As a proof of concept, we developed an algorithm that automatically optimizes the stimulation orientation based on single-trial EEG responses. We applied the algorithm to determine the electric field orientation that maximizes the amplitude of the TMS-EEG responses. The validation of the algorithm was performed with six healthy volunteers, repeating the search twenty times for each subject.

Results: The validation demonstrated that the closed-loop control worked as desired despite the large variation in the single-trial EEG responses. We were often able to get close to the orientation that maximizes the EEG amplitude with only a few tens of pulses.

Conclusion: Optimizing stimulation with EEG feedback in a closed-loop manner is feasible and enables effective coupling to brain activity.

Keywords: Bayesian optimization; Closed-loop; Electroencephalography; Multi-channel TMS; Multi-locus TMS; Transcranial magnetic stimulation.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Brain / physiology
Brain Mapping
Electroencephalography*
Feedback
Humans
Transcranial Magnetic Stimulation*