Cognitive neural mechanisms of face-to-face interpersonal synchronous stepping: An fNIRS study

Interpersonal movement coordination involves the organized, synchronized execution of actions between individuals. The spatial configuration of co-actors (e.g., side-by-side vs. face-to-face) modulates coordination dynamics, likely due to differences in the availability and processing of action-related perceptual information. This study employed a face-to-face stepping paradigm with sixteen dyads to investigate how different coordination modes (in-phase vs. anti-phase) engage these neural systems compared to individual performance. Using functional near-infrared spectroscopy (fNIRS) hyperscanning to record cerebral hemodynamic responses simultaneously from both partners, we examined the behavioral and neural correlates of interpersonal synchronization. To quantify neural coupling between partners, we computed wavelet transform coherence as a measure of inter-brain synchronization. The experimental results showed that (1) behaviorally, the inter-individual coordination index revealed that individuals showed higher coherence when coordinating in the mirror-symmetric direction as compared to non-mirror symmetric mode, (2) cerebral activity was lower in the frontal-parietal region during coordination of pairs executing movements face-to-face as compared to stepping alone, and (3) inter-brain synchronization was significantly enhanced during both interpersonal coordination modes compared to solo stepping, indicating strengthened neural coupling between partners during coordinated action. This pattern suggests that face-to-face coordination promotes neural efficiency through coupled predictive processing between partners.