Learning with others: teacher-learner brain synchrony depends on mutual gaze and joint attention.

Successful learning often emerges through social interaction: what are the neural and behavioral systems that support this process? This ecological, multimodal study combines functional near-infrared spectroscopy hyperscanning with detailed behavioral and physiological measures in 27 unconstrained social learning interactions. Learning was supported by teacher-learner interbrain synchrony (interpersonal neural synchrony), over regions important for mutual understanding (temporoparietal junction) and communicative coordination (ventral premotor cortex). Joint attention and mutual gaze modulated the interpersonal neural synchrony-learning association in oppositive ways, motivating a dual-process model: during knowledge-building phases, learning is supported by informational uptake dynamic, with high joint attention, low interpersonal neural synchrony in regions for mutual understanding (temporoparietal junction) and coordination (right ventral premotor cortex), and high interpersonal neural synchrony in language-related areas (left ventral premotor cortex). In contrast, during moments of mutual grounding, learning is supported by high mutual gaze and high interpersonal neural synchrony over temporoparietal junction. Cross-brain general linear modeling revealed asymmetric neural dependencies linked to speaking and teaching roles in the left-hemisphere language network. These effects remained after controlling for nodding, gaze, and breathing, indicating that interpersonal neural synchrony reflects true social-cognitive alignment beyond sensorimotor coupling. Taken together, this study shows that successful learning arises from coordinated and nonlinear brain-body dynamics and positions interpersonal neural synchrony as a marker of mutual prediction during communicative social interaction.