Analyzing Emotional Facial Expressions’ Neural Correlates Using Event-Related Potentials and Eye Fixation-Related Potentials

The processing of emotional facial expressions (EFE) elicits specific evoked brain responses reflecting different stages of the EFE processing. Here, we focus on the Late Positive Potential (LPP; around 500ms) as a marker of an elaborative processing and conscious recognition of EFE involving the working memory. But at this latency, during visual exploration, the Event-Related Potential (ERP) at the stimuli onset and the Eye Fixation-Related Potential (EFRP) at the first fixation onset overlap. Using a General Linear Model, these potentials can be identified separately. Methods. Twenty-four participants were asked to freely empathize with the presented EFE (70 natural but standardized EFE -Neutral, Disgust, Surprise, Happiness- before categorizing them. Results. Around 200ms, early posterior neural activities of the first EFRP were modulated by EFE (Happiness vs Disgust). During the LPP latency, this modulation provided by cognitive processing from this fixation onset (mean 275ms), strengthened an activities pattern at left frontal sites -more involved for positive EFE- becoming significant across EFE. In contrast, at right frontal sites -more involved for negative EFE, another activities pattern, only elicited by the stimuli presentation, was significant across EFE. Moreover, taken together, these findings are in line with faster and facilitated perceptual processing for negative EFE.