Integrating neural, physiological, and interoceptive measures in social interaction.

Social interaction is not simply the meeting of two brains, but the emergent product of continuously coupled brain-body systems within and between individuals. Hyper scanning studies have shown that interacting partners exhibit inter-brain synchrony during cooperation, conversation, and joint attention, consolidating neural coupling as a marker of shared engagement. Yet neural data alone cannot tell us whether individuals are aligned in their emotions, arousal, or regulatory strategies, nor how these states evolve in real time. In parallel, work on physiological synchrony has revealed that partners' autonomic signals also converge during interaction, tracking rapport, cohesion, and cooperative success. Interoception, the sensing and representation of internal bodily signals, provides a conceptual bridge between these levels. Atypical interoceptive processing is increasingly implicated across conditions marked by social difficulties, and emerging hyper scanning studies show that directing attention to bodily rhythms can enhance both autonomic and neural alignment. In this Perspective, I argue for a framework in which social behavior arises from multilevel coupling among neural activity, autonomic physiology, and interoceptive processes. I outline how multimodal hyperscanning in naturalistic tasks, combined with temporally sensitive analyses, can clarify when and how these levels interact, from dyads to groups. Finally, I discuss clinical and developmental horizons in which multimodal synchrony serves both as a mechanistic readout and a potential target for interventions that stabilize internal dynamics to support social connection.