EEG Recorded from the Ear: Characterizing the Ear-EEG Method.

Kaare B Mikkelsen,Simon L Kappel,Danilo P Mandic,Preben Kidmose

doi:10.3389/fnins.2015.00438

Kaare B Mikkelsen, Simon L Kappel + Show 2 more

Open Access

https://doi.org/10.3389/fnins.2015.00438

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Abstract

Highlights Auditory middle and late latency responses can be recorded reliably from ear-EEG.For sources close to the ear, ear-EEG has the same signal-to-noise-ratio as scalp.Ear-EEG is an excellent match for power spectrum-based analysis.A method for measuring electroencephalograms (EEG) from the outer ear, so-called ear-EEG, has recently been proposed. The method could potentially enable robust recording of EEG in natural environments. The objective of this study was to substantiate the ear-EEG method by using a larger population of subjects and several paradigms. For rigor, we considered simultaneous scalp and ear-EEG recordings with common reference. More precisely, 32 conventional scalp electrodes and 12 ear electrodes allowed a thorough comparison between conventional and ear electrodes, testing several different placements of references. The paradigms probed auditory onset response, mismatch negativity, auditory steady-state response and alpha power attenuation. By comparing event related potential (ERP) waveforms from the mismatch response paradigm, the signal measured from the ear electrodes was found to reflect the same cortical activity as that from nearby scalp electrodes. It was also found that referencing the ear-EEG electrodes to another within-ear electrode affects the time-domain recorded waveform (relative to scalp recordings), but not the timing of individual components. It was furthermore found that auditory steady-state responses and alpha-band modulation were measured reliably with the ear-EEG modality. Finally, our findings showed that the auditory mismatch response was difficult to monitor with the ear-EEG. We conclude that ear-EEG yields similar performance as conventional EEG for spectrogram-based analysis, similar timing of ERP components, and equal signal strength for sources close to the ear. Ear-EEG can reliably measure activity from regions of the cortex which are located close to the ears, especially in paradigms employing frequency-domain analyses.

Highlights

Electroencephalography (EEG) is a well established technique (Pravdich-Neminsky, 1913), providing valuable insights into brain activity, with applications both in clinical practice and in basic and applied neuroscience (Nunez and Srinivasan, 2007).Despite the widespread adoption, a number of important applications of EEG are prohibited by the requirements for mobility and discreetness of the EEG equipment used
Considering that the distance to the reference electrode (Cz) was large compared to the distance between the measuring electrodes, it is not surprising that the potentials measured from the ear electrodes were essentially the same as the potentials measured from nearby temporal region ear-EEG channels was 22.1 ± 8.5, while for TP9/TP10 it was 21.8 ± 4.0, after averaging 240 segments
By referencing the ear electrodes to the scalp Cz electrode and comparing measurements to Cz-referenced temporal electrodes, we have demonstrated the feasibility of placing EEG electrodes inside the ear canal in such a way that both a reliable connection and a signal quality similar to that of a conventional scalp electrode can be maintained

Summary

Introduction

Electroencephalography (EEG) is a well established technique (Pravdich-Neminsky, 1913), providing valuable insights into brain activity, with applications both in clinical practice and in basic and applied neuroscience (Nunez and Srinivasan, 2007).Despite the widespread adoption, a number of important applications of EEG are prohibited by the requirements for mobility and discreetness of the EEG equipment used. Electroencephalography (EEG) is a well established technique (Pravdich-Neminsky, 1913), providing valuable insights into brain activity, with applications both in clinical practice and in basic and applied neuroscience (Nunez and Srinivasan, 2007). Examples include brain-computer interfaces (BCI), long-term monitoring of neurological patients and sleep monitoring. To this end, several EEG recording methods have recently been proposed (Casson et al, 2010; Debener et al, 2012), including some which benefit from a relatively unrestricted access to the area around and inside the ears (Looney et al, 2012; Bleichner et al, 2015; Norton et al, 2015). Our aim was to provide a thorough and self-sufficient reference for practitioners, regarding the feasibility of the ear-EEG method for the wider multi-disciplinary EEG community

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