From lab to living room: evaluating the signal quality of water-based EEG

Abstract

Scalp electroencephalography (EEG) is a widely used, noninvasive tool to assess brain activity. EEG is valuable for various neurological conditions like epilepsy and migraine. Conventional EEG uses gel-based electrodes, ensuring good signal quality but requiring complex setup and the removal of patients from their natural environments. Portable EEG devices with water electrodes offer easier home measurements but pose signal quality concerns. This thesis aims to evaluate the signal quality of water electrodes compared to gel electrodes and investigate the feasibility of home-based EEG measurements.
Three experimental protocols were used: resting-state (RS), single visual evoked potentials (SVEP) and 12 Hz steady-state visual evoked potentials (SSVEP). These signals were measured 1) in the lab, once with a gel cap and once with a water cap; and 2) at home with a water cap. Signal quality was assessed with the artefact proportion, the signal-to-noise ratio (SNR), the relative 12 Hz SSVEP power, the relative alpha band eyes-closed RS power, the presence of the Berger effect, and the SVEP waveforms.
In the lab setting, the water and gel cap showed similar signal quality as illustrated by a similar SNR, relative alpha power, alpha band presence and SVEP waveform. However, an increase in artefacts and slight decrease in relative 12 Hz power and SVEP amplitude show remaining shortcomings of the water cap compared to the gel cap. When comparing the water cap between lab and home settings, the performance closely matches. This is demonstrated by the similar SNR, relative 12 Hz power, alpha presence and SVEP waveform and amplitude. Differences were a decrease in artefacts and an increase in relative alpha band power for the signal measured at home.
Provided that the limitations of the water cap can be mitigated by further developments, the otherwise relatively comparable signal quality between the gel and water caps suggests that water-based EEG systems could be a viable alternative to traditional gel-based systems. Furthermore, the positive home study results suggest that home-based EEG measurements could be a viable alternative to lab-based studies with the help of a water electrode EEG cap.