Distinct Fusiform Subregion Activity and Connectivity in Lonely and Non-lonely Individuals During Social Information Processing

Loneliness has been recognized as a major public health concern affecting individuals' everyday social functioning. Although hypothesized, the association between chronic loneliness, neural responses, and parasympathetic regulation during social information processing remains underexplored. This study aimed to compare parasympathetic and neural responses to affective social content in well-powered samples of participants with different chronic loneliness levels. In this study, 104 (52 females) healthy young adults were recruited based on their chronic loneliness levels to form groups of lonely (LI) and non-lonely (NLI) individuals. Participants underwent a functional magnetic resonance imaging session in which they passively viewed social and non-social images of negative, positive, and neutral valence. Both groups showed similar task-related vagal changes and responses across predefined regions associated with key social brain areas. However, an exploratory whole-brain activity analysis revealed between-group differences in two distinct fusiform face area (FFA) subregions. Furthermore, the LI group showed decreased connectivity between one of the FFA subregions and right temporoparietal junction compared to the NLI group. These results suggest that trait-like loneliness is associated with distinct processing of social content in FFA subregions, potentially linking loneliness to differences in effective social information integration.