Insular intracranial activity identifies multiple facial expressions via diverse, intermixed temporal patterns at the single-contact level

How neural representations in the insular cortex support emotional processing remains poorly understood, and the extent to which the insula is specialized for disgust processing remains debated. We recorded stereoelectroencephalography data from the insula while human subjects with implanted electrode contacts performed a facial emotion recognition task involving disgusted, fearful, angry, sad, neutral, and happy expressions. Expression category specificity of insular activity was assessed via pairwise comparisons of within- and between-category pattern similarities, capturing both the shape and scale of event-related potentials (ERPs) and event-related spectral perturbations (ERSPs; theta to high-gamma frequency ranges). Insular activity successfully identified all investigated expressions, mediated by diverse ERP responses intermixed across the insula. In contrast to the marked heterogeneity of insula ERP responses, the fusiform face area exhibited convergent ERP responses across expressions and contacts, with ERSPs also contributing substantially to expression identification. These findings not only elucidate the insula's neural mechanisms underlying facial emotion perception, but also establish a potential single-contact-level neural substrate for how the insula leverages its heterogeneous response profiles to act as a key hub for versatile cognitive and emotional functions.