THE CHALLENGING SCALP–ELECTRODE INTERFACE AND THE EVOLUTION OF MATERIALS AND ELECTRODE INTEGRATED ICTs FOR ELECTROENCEPHALOGRAPHY

Electroencephalography (EEG) is a non-invasive technique used to measure the electrical activity of the brain. The use of EEG is very important for the diagnosis of traumatic brain events and mental states such as injury, stroke, depression and many others including the COVID-19 brain fog syndrome. The quality of EEG signals largely depends on the nature of the interface between the surface of the electrode material and the surface of the scalp from where the electrical brain signals are acquired. The scalp surface is composed of an epidermic substrate with hair, grease, dirt, dandruff, skin peels and eventually many different hair products. The electrodes must combine several properties including electrical conductivity, mechanical strength, biocompatibility and corrosion resistance. They also must be manufactured with shapes designed to overcome the inherently complex nature of the scalp–electrode interface. This review reports the latest advances in the design of materials, surface coatings, conductive gels and information and communication technologies being developed to increase the quality of measurement of brain electrical signals in EEG protocols.