Mentalizing from self and friend perspectives: Relations between inter-brain neural similarity, affective similarity and social anxiety symptoms.

Social interactions are dynamic and complex, relying on tracking variation in your own and your partner's affective and mental states. Being "in-sync" neurally and building a shared consensus can mark successful social interactions. In addition, social anxiety can impact social experiences. We used a novel, naturalistic paradigm to investigate relations between inter-brain neural similarity within mentalizing regions, affective similarity, and social anxiety symptoms. Undergraduate student friend pairs (N = 34, 85% White, 65% Women) engaged in a social interaction while videos captured from their individual perspectives were recorded. Participants watched clips of the social interaction from both their own perspective (their personal view of the social interaction) and their friend's perspective (their friend's personal view of the social interaction) while fMRI data were collected. They rated their affect after each clip. Inter-brain neural similarity was computed across three conditions: 1) Same-Stimuli: both participants viewed identical visual stimuli as in a traditional neural similarity paradigm, 2) Self-Perspective: both participants viewed the clip from their own perspective like the originally experienced social interaction, and 3) Friend-Perspective: both participants viewed the clip from their friend's perspective, a novel perspective. Participants self-reported their social anxiety symptoms, and affective similarity captured affect rating concordance within dyads. In contrast to the Same-Stimuli condition, when participants viewed the clips like they originally experienced the social interaction (Self-Perspective), greater affective similarity was associated with greater inter-brain neural similarity. When participants viewed the clips from a novel perspective (Friend-Perspective), participants lower in social anxiety symptoms exhibited greater inter-brain neural similarity with greater affective similarity; whereas participants higher in social anxiety symptoms exhibited greater inter-brain neural similarity with less affective similarity. The results suggest stimuli from socially relevant perspectives, rather than identical stimuli, may reveal more nuanced brain-behavior dynamics, allowing for a better understanding of individual differences in socioemotional experience.