Distinct fusiform subregion activity and connectivity in lonely and nonlonely 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 and nonlonely individuals. Participants underwent a functional magnetic resonance imaging session in which they passively viewed social and nonsocial 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 subregions. Furthermore, the lonely individuals group showed decreased connectivity between one of the fusiform face area subregions and right temporoparietal junction compared to the nonlonely individuals group. These results suggest that trait-like loneliness is associated with distinct processing of social content in fusiform face area subregions, potentially linking loneliness to differences in effective social information integration.