Tripolar concentric ring electrode electroencephalography using Signa gel for impedance matching

Our goal is to develop a high-spatial resolution and high signal-to-noise electroencephalography (EEG) recording system. Conventional scalp EEG is contaminated by noise represented by non-brain electrical activity such as ocular artifacts, scalp muscle potentials, electrocardiogram, etc. Conventional disc EEG recordings also have reference electrode problems. To overcome the problems of the disc electrodes (Fig. 1. A) we have developed the tripolar concentric ring electrode (TCRE). The TCRE consists of three electrode elements - outer ring, middle ring, and the central disc (Fig. 1, B). In the past we have always used Ten20 paste to attach the TCREs and match skin to electrode impedances. For many electrodes, say 64 or more, it would be time consuming to use Ten20 paste. In this study we demonstrate that Signa gel on TCREs acts as an effective means to match electrode impedances to the scalp. We recorded physiological brain signals using Signa gel and our 10 mm diameter TCREs. The EEG signals we recorded with the TCREs (tEEG) originated from alpha wave activity. A conventional disc electrode (CDE) next to the TCRE was used to record EEG for comparison. We believe that 10 mm TCREs, and gel used for impedance matching, are appropriate when many TCREs are needed for high spatial sampling.