Generic Dry-Contact Ear-EEG.

Generic dry-contact ear-EEG allows for discreet, user-friendly, unobtrusive, cost-effective and convenient recordings of EEG in real-life settings. In this study we introduce a new generic earpiece design with larger internal ear electrode distances, resulting in an increased spatial coverage compared to previous generic earpiece designs. The signal quality of ear-Fpz, within-ear (the measuring and reference electrode located in the same ear) and cross-ear (the measuring electrodes located in one ear and the reference electrode in the opposite ear) electrode configurations of the developed generic earpiece was evaluated with auditory steady-state responses (ASSR) and compared to dry-contact cEEGrid. Ten subjects with different ear sizes were included. The recordings were performed in a sleep setup, where the subjects were lying on a bed and the effect of sleeping position (back vs. sides) was investigated. We found that the generic earpiece attained statistically significant ASSRs with ear-Fpz, within-ear and cross-ear electrode configurations. However, the dry-contact cEEGrid achieved significantly higher average ASSR signal-to-noise ratio (SNR) compared to the generic earpiece. Additionally, this study showed no significant difference between back and side positions for the ear-EEG.

Auditory Steady-State Responses Across Chirp Repetition Rates For Ear-EEG And Scalp EEG.

Measurement of auditory steady-state responses (ASSR) using ear-EEG potentially enables objective audiometry out of the clinic in the everyday life of hearing aid users. As ear-EEG are measured from electrodes placed within the ear, electrode distances are inherently small and consequently the potential differences, and thereby signal amplitudes, are also small. Because the detection of the ASSR is based on the signalto-noise ratio (SNR), it is of fundamental interest to know the inherent SNR of the ASSR as a function of the stimulus repetition rate. In this study, ASSRs were recorded using both scalp and ear-EEG in response to broadband chirp stimuli with repetition rates from 20 to 95 Hz. The results showed that in general ear-EEG and scalp EEG SNR was on par across repetition rates; an exception to this was at rates around 40 Hz where the SNR was significantly lower for ear-EEG as compared to scalp EEG. For ear-EEG, the ASSR was relatively constant across repetition rates, whereas the noise showed a 1/f characteristic. In consequence, there was a tendency to increased SNR as a function of repetition rate. This suggests that use of relatively high repetition rates may be beneficial in earEEG applications.

Detection of generalized tonic-clonic seizures from ear-EEG based on EMG analysis.

PURPOSE: Sudden unexpected death in epilepsy (SUDEP) is associated with generalized tonic-clonic seizures (GTCS) with most deaths occurring during sleep. Seizure detection devices have been suggested as a SUDEP prevention strategy. EMG-based GTCS detection can take advantage of the GTCS characteristic of sustained high-amplitude, high-frequency activity in the time-domain. METHOD: We present a GTCS-detection method based on median-filtered variance estimates on surface EMG measurements and describe its performance in a small exploratory proof-of-concept setting involving a group of 15 patients with 3 GTCS recorded with ear-EEG and another group of 6 patients with 11 GTCS recorded with scalp-EEG. RESULTS: GTCS intervals were detected within 4.2-12.9 s of onset with 100% sensitivity (CI 29.2-100%) without false positives in 820.7 h of ear-EEG. The same detection method worked for the 11 GTCS from scalp EEG data with 100% sensitivity (CI 71.5-100%) and no false positives. CONCLUSIONS: Ear-EEG contains enough GTCS-specific EMG activity for GTCS detection to be feasible. Ear-EEG could be considered for nocturnal GTCS monitoring as a supplement to SUDEP preventive interventions.

Ear-EEG detects ictal and interictal abnormalities in focal and generalized epilepsy - A comparison with scalp EEG monitoring.

OBJECTIVE: Ear-EEG is recording of electroencephalography from a small device in the ear. This is the first study to compare ictal and interictal abnormalities recorded with ear-EEG and simultaneous scalp-EEG in an epilepsy monitoring unit. METHODS: We recorded and compared simultaneous ear-EEG and scalp-EEG from 15 patients with suspected temporal lobe epilepsy. EEGs were compared visually by independent neurophysiologists. Correlation and time-frequency analysis was used to quantify the similarity between ear and scalp electrodes. Spike-averages were used to assess similarity of interictal spikes. RESULTS: There were no differences in sensitivity or specificity for seizure detection. Mean correlation coefficient between ear-EEG and nearest scalp electrode was above 0.6 with a statistically significant decreasing trend with increasing distance away from the ear. Ictal morphology and frequency dynamics can be observed from visual inspection and time-frequency analysis. Spike averages derived from ear-EEG electrodes yield a recognizable spike appearance. CONCLUSIONS: Our results suggest that ear-EEG can reliably detect electroencephalographic patterns associated with focal temporal lobe seizures. Interictal spike morphology from sufficiently large temporal spike sources can be sampled using ear-EEG. SIGNIFICANCE: Ear-EEG is likely to become an important tool in clinical epilepsy monitoring and diagnosis.

Case comparison of sleep features from ear-EEG and scalp-EEG.

BACKGROUND: We investigate the potential usability of a novel in-the-ear electroencephalography recording device for sleep staging. METHODS: In one healthy subject we compare simultaneous earelectroencephalography to standard scalp EEG visually and using power spectrograms. Hypnograms independently derived from the records are compared. RESULTS: We find that alpha activity, K complexes, sleep spindles and slow wave sleep can be visually distinguished using earelectroencephalography. Spectral peaks are shared between the two records. Hypnograms are 90.9% similar. CONCLUSION: The results indicate that ear-electroencephalography can be used for sleep staging.

Ear-EEG from generic earpieces: a feasibility study.

The use of brain monitoring based on EEG, in natural environments and over long time periods, is hindered by the limited portability of current wearable systems, and the invasiveness of implanted systems. To that end, we introduce an ear-EEG recording device based on generic earpieces which meets key patient needs (discreet, unobstrusive, user-friendly, robust) and that is low-cost and suitable for off-the-shelf use; thus promising great advantages for healthcare applications. Its feasibility is validated in a comprehensive comparative study with our established prototype, based on a personalized earpiece, for a key EEG paradigm.

Auditory evoked responses from Ear-EEG recordings.

A method for brain monitoring based on measuring electroencephalographic (EEG) signals from electrodes placed in-the-ear (Ear-EEG) was recently proposed. The Ear-EEG recording methodology provides a non-invasive, discreet and unobtrusive way of measuring electrical brain signals and has great potential as an enabling method for brain monitoring in everyday life. This work aims at further establishing the Ear-EEG recording methodology by considering auditory evoked potentials, and by comparing Ear-EEG responses with conventional on-scalp recordings and with well established results from the literature. It is shown that both steady state and transient responses can be obtained from Ear-EEG, and that these responses have similar characteristics and quality compared to EEG obtained from conventional on-scalp recordings.

An in-the-ear platform for recording electroencephalogram.

We introduce a novel approach to brain monitoring based on electroencephalogram (EEG) recordings from within the ear canal. While existing clinical and wearable systems are limited in terms of portability and ease of use, the proposed in-the-ear (ITE) recording platform promises a number of advantages including ease of implementation, minimally intrusive electrodes and enhanced accuracy (fixed electrode positions). It thus facilitates a crucial step towards the design of brain computer interfaces that integrate naturally with daily life. The feasibility of the ITE concept is demonstrated with recordings made from electrodes embedded on an earplug which are benchmarked against conventional scalp electrodes for a classic EEG paradigm.

An adaptive algorithm for real-time electrode calibration.

Continuous brain monitoring based on EEG recorded from surface electrodes is believed to have potentials in wearable medical devices. In such devices capacitive electrodes are attractive compared to conventional electrodes because there is no need for skin preparation and conductive gels, and because of diminished motion artifacts. However, there are technical challenges connected to the practical application of capacitive electrodes. The electrode capacitance, which has significant impact on the signal measured, will vary between channels and will be time varying. Therefore calibration of the electrode array is an important preprocessing step before the signal processing. This paper proposes an algorithm for blindly estimating the parameters of the analog signal acquisition paths, including the capacitances of the electrodes. The algorithm continuously estimates the parameters, based on the measured EEG signals, and compensates for variations in the analog signal paths. Simulations show that the algorithm can estimate the parameters, and track changes of the electrodes capacitance in real-time.

A Yarbus-style experiment to determine auditory attention.

This paper presents an analysis of the merits of the original Yarbus experiment on eye movements with respect to judgments on differences in cognitive layer processes. The principles thus derived are applied to the development of an equivalent auditory experiment where, instead of eye movements, the response of the subject is observed by EEG measurements. Results from a preliminary trial are also included in which EEG analysis is used to ascertain the attended sound source in a multiple sound source environment. The investigation is part of ongoing research to improve the usefulness of hearing instruments and is also relevant in relation to other scientific investigations concerning the processing of sounds in complex acoustical environments by the human brain.