Wearable EEG and beyond

Abstract

The electroencephalogram (EEG) is a widely used non-invasive method for monitoring the brain. It is based upon placing conductive electrodes on the scalp which measure the small electrical potentials that arise outside of the head due to neuronal action within the brain. Historically this has been a large and bulky technology, restricted to the monitoring of subjects in a lab or clinic while they are stationary. Over the last decade much research effort has been put into the creation of "wearable EEG" which overcomes these limitations and allows the long term non-invasive recording of brain signals while people are out of the lab and moving about. This paper reviews the recent progress in this field, with particular emphasis on the electrodes used to make connections to the head and the physical EEG hardware. The emergence of conformal "tattoo" type EEG electrodes is highlighted as a key next step for giving very small and socially discrete units. In addition, new recommendations for the performance validation of novel electrode technologies are given, with standards in this area seen as the current main bottleneck to the wider take up of wearable EEG. The paper concludes by considering the next steps in the creation of next generation wearable EEG units, showing that a wide range of research avenues are present.

Electrical properties, accuracy, and multi-day performance of gelatine phantoms for electrophysiology

“…Electrophysiological sensing, measuring the electrical activity of the brain (electroencephalography, EEG), heart (electrocardiography, ECG), muscles (electromyography, EMG), and eyes (electrooculography, EOG), is an extremely common technique used in both clinical practice and fundamental research [1]. While electrophysiological sensing instrumentation is well developed, there are significant ongoing research efforts into improving the sensing performance [2]. This is in terms of both the hardware, making it smaller, more robust to artefacts and easier to use (for example [3], [4]), and the electrodes, with a wide range of electrode materials and approaches investigated in recent years (for example [5], [6]).…”

“…However, this introduces ethical or animal license considerations, and is labour intensive, both of which limit the rapid, iterative, and large scale screening of different electrode approaches. Moreover, when using a human or animal model the true electrophysiological signal present is not known, which makes the validation of systems very challenging as no ground truth is available to compare against [2].…”

“…The result is that a wide number of different materials have been investigated for making electrophysiology body phantoms (gelatine [2], [5], [13], [15], [16], wax [28], silicon [28], [14]. Image taken from the public domain [20].…”

“…(c) Head phantom from our lab with two internal electrodes for replaying a pre-recorded signal which can be collected by electrodes on the phantom surface. Reprinted by permission from Springer Nature: Biomedical Engineering Letters, [2], c 2019. (d) Head phantom from our lab for EEG combined with brain stimulation (tES electrodes labelled as unused in this picture).…”

Wireless, Skin-Mountable EMG Sensor for Human–Machine Interface Application

“…Recently, as the integration technology of semiconductors developed, devices and sensors decreased in size, enabling various novel applications, including wearable sensors [1][2][3][4]. In particular, non-invasive wearable sensors collecting electrical signals from electrodes attached to the skin are used as key tools for obtaining various biosignals, such as electrocardiography (ECG) [5,6], surface electromyography (sEMG) [7], electromyography (EMG) [8,9], electroencephalography (EEG) [10], and so forth. These sensors are used in the medical field for the diagnosis of disease states or the monitoring of health conditions.…”