Investigating the neural origins of Ear-EEG: A correlation study using scalp EEG source reconstruction

Ear electroencephalography (Ear-EEG) has emerged as a promising alternative to traditional scalp EEG, offering a noninvasive, discreet, and portable method for neural monitoring. While its ability to capture brain activity is established, the cortical origins of Ear-EEG signals remain unclear. It is uncertain whether these signals primarily reflect activity from nearby cortical regions or volume-conducted signals from distant areas. This study investigates the cortical sources of Ear-EEG signals and their relationship to neural activity across frequency bands, including alpha rhythms, sleep spindles, and slow waves. We simultaneously recorded Ear-EEG (1-channel, dry-contact) and high-density scalp EEG (64-channel, wet-contact) from healthy participants during wakeful rest and sleep. Source localization and correlation analyses across 34 regions of interest (ROIs) were used to identify the cortical origins of Ear-EEG and examine how signal strength relates to proximity to the ear canal. Results revealed significant correlations between Ear-EEG and cortical activity, particularly in the temporal, prefrontal, and cingulate regions. Correlation strength decreased with increasing distance from the ear canal, suggesting that Ear-EEG primarily reflects nearby cortical activity. Comparisons with T7-T8 scalp electrodes showed similar correlation patterns, reinforcing the reliability of Ear-EEG for neurophysiological monitoring. These findings confirm that dry-contact Ear-EEG captures meaningful neural activity from specific cortical regions and highlight its potential for portable brain monitoring. Identifying its cortical sources provides a foundation for optimizing electrode placement and system design, advancing the development of Ear-EEG technology.