Scalp electroencephalography (EEG) serves as a pivotal technology for the noninvasive monitoring of brain functional activity, diagnosing neurological disorders, and assessing cognitive states. However, inherent compatibility barriers between traditional rigid electrodes and the hairy scalp interface significantly compromise signal quality, long-term monitoring comfort, and user compliance. This review examines conductive hydrogel electrodes' pivotal role in advancing scalp EEG, particularly their unique capacity to overcome hair-interface barriers. The superiority of scalp EEG is first established over forehead/ear EEG for capturing diverse neural signals and defining core requirements for hair-compatible interfaces: scalp conformability, electrical conductivity, low contact impedance, and interfacial stability. Conductive hydrogel electrode applications are then detailed in alpha wave detection, sleep monitoring, event-related potential studies, and brain-computer interfaces. Finally, persisting challenges and future opportunities are discussed.
Ji et al. (Sat,) studied this question.