The Sensitivity of Ear-EEG: Evaluating the Source-Sensor Relationship Using Forward Modeling
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ORIGINAL PAPER
The Sensitivity of Ear‑EEG: Evaluating the Source‑Sensor Relationship Using Forward Modeling Arnd Meiser1 · Francois Tadel2 · Stefan Debener1 · Martin G. Bleichner1 Received: 10 March 2020 / Accepted: 12 August 2020 © The Author(s) 2020
Abstract Ear-EEG allows to record brain activity in every-day life, for example to study natural behaviour or unhindered social interactions. Compared to conventional scalp-EEG, ear-EEG uses fewer electrodes and covers only a small part of the head. Consequently, ear-EEG will be less sensitive to some cortical sources. Here, we perform realistic electromagnetic simulations to compare cEEGrid ear-EEG with 128-channel cap-EEG. We compute the sensitivity of ear-EEG for different cortical sources, and quantify the expected signal loss of ear-EEG relative to cap-EEG. Our results show that ear-EEG is most sensitive to sources in the temporal cortex. Furthermore, we show how ear-EEG benefits from a multi-channel configuration (i.e. cEEGrid). The pipelines presented here can be adapted to any arrangement of electrodes and can therefore provide an estimate of sensitivity to cortical regions, thereby increasing the chance of successful experiments using ear-EEG. Keywords Ear-EEG · Ear-centered sensing · Forward modeling · cEEGrid · Cortical folding · Sensitivity map
Introduction Ear-EEG (electroencephalography) opens up new possibilities to record brain activity beyond the lab with minimal inconvenience for a person (Debener et al. (2015); Bleichner and Debener (2017)). For instance, ear-EEG could become an integral part for medical applications like epilepsy- (Zibrandtsen et al. (2017)) or sleep-monitoring (Looney et al. (2016); Nakamura et al. (2017)) as well as attention tracking (Mirkovic et al. (2016)) or as part of hearing devices (Fiedler et al. (2016); Denk et al. (2018)). The goal of ear-EEG is to measure brain-electrical activity in natural, daily life conditions and over long periods of time. With classical, stationary EEG, including a larger number Handling Editor: Christoph M. Michel. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10548-020-00793-2) contains supplementary material, which is available to authorized users. * Arnd Meiser arnd.meiser@uni‑oldenburg.de 1
Department of Psychology, University of Oldenburg, Oldenburg, Germany
Montreal Neurological Institute, McGill University, Montreal, Canada
2
of scalp electrodes, cables and additional necessary equipment, measuring under real-life conditions is difficult. To this end, an ear-EEG system ideally avoids those issues and is no more visible or distracting than a hearing device or glasses. Of course, this puts constraints on the number and the placement of the few available electrodes. There are two different approaches tackling this problem: one is in-ear-EEG, where electrodes are either placed in the outer ear canal or the concha (Kidmose et al. (2012); Looney et al. (2012); Lee et al. (2014); Fiedler et al. (2017)). The second approach is
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