Removing artifacts from TMS-evoked EEG: A methods review and a unifying theoretical framework

Julio C Hernandez-Pavon; Dimitris Kugiumtzis; Christoph Zrenner; Vasilios K Kimiskidis; Johanna Metsomaa

doi:10.1016/j.jneumeth.2022.109591

Removing artifacts from TMS-evoked EEG: A methods review and a unifying theoretical framework

J Neurosci Methods. 2022 Jul 1:376:109591. doi: 10.1016/j.jneumeth.2022.109591. Epub 2022 Apr 11.

Authors

Julio C Hernandez-Pavon¹, Dimitris Kugiumtzis², Christoph Zrenner³, Vasilios K Kimiskidis⁴, Johanna Metsomaa⁵

Affiliations

¹ Legs + Walking Lab, Shirley Ryan AbilityLab (Formerly The Rehabilitation Institute of Chicago), Chicago, IL, USA; Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA; Center for Brain Stimulation, Shirley Ryan AbilityLab, Chicago, IL, USA. Electronic address: jpavon@sralab.org.
² Department of Electrical and Computer Engineering, Faculty of Engineering, Aristotle University of Thessaloniki, Thessaloniki, Greece.
³ Department of Neurology & Stroke, and Hertie Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany; Temerty Centre for Therapeutic Brain Intervention, Centre for Addiction and Mental Health, Toronto, ON, Canada; Department of Psychiatry, University of Toronto, Toronto, ON, Canada.
⁴ 1st Department of Neurology, Medical School, Aristotle University of Thessaloniki, Thessaloniki, Greece.
⁵ Department of Neurology & Stroke, and Hertie Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany; Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland. Electronic address: johanna.metsomaa@aalto.fi.

PMID: 35421514
DOI: 10.1016/j.jneumeth.2022.109591

Abstract

Transcranial magnetic stimulation (TMS) combined with electroencephalography (EEG) is a technique for studying cortical excitability and connectivity in health and disease, allowing basic research and potential clinical applications. A major methodological issue, severely limiting the applicability of TMS-EEG, relates to the contamination of EEG signals by artifacts of biologic or non-biologic origin. To solve this problem, several methods, based on independent component analysis (ICA), principal component analysis (PCA), signal space projection (SSP), and other approaches, have been developed over the last decade. This article is divided into two parts. In the first part, we review the theoretical background of the currently available TMS-EEG artifact removal methods. In the second part, we formally introduce the mathematics underpinnings of the cleaning methods. We classify them into spatial and temporal filters based on their properties. Since the most frequently used TMS-EEG cleaning approach are spatial filter methods, we focus on them and introduce beamforming as a unified framework of the most popular spatial filtering techniques. This unifying approach enables the comparative assessment of these methods by highlighting their differences in terms of assumptions, challenges, and applicability for different types of artifacts and data. The different properties and challenges of the methods discussed are illustrated with both simulated and recorded data. This article targets non-mathematical and mathematical audiences. Accordingly, those readers interested in essential background information on these methods can focus on Section 2. Whereas theory-oriented readers may find Section 3 helpful for making informed decisions between existing methods and developing the methodology further.

Keywords: Artifacts; Beamforming; Electroencephalography; Independent component analysis; Principal component analysis; Signal space projection; Spatial filters; Temporal filters; Transcranial magnetic stimulation.

Publication types

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

MeSH terms

Artifacts*
Electroencephalography / methods
Principal Component Analysis
Transcranial Magnetic Stimulation* / methods