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 behavioural systems that support this process? This ecological, multimodal study combines functional near-infrared spectroscopy (fNIRS) hyperscanning with detailed behavioural and physiological measures in 27 unconstrained social learning interactions. Learning was supported by teacher-learner inter-brain synchrony (INS), over regions important for mutual understanding (temporo-parietal junction, TPJ) and communicative coordination (ventral premotor, PMv). Joint attention and mutual gaze modulated the INS-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 INS in regions for mutual understanding (TPJ) and coordination (right PMv), and high INS in language-related areas (left PMv). In contrast, during moments of mutual grounding, learning is supported by high mutual gaze and high INS over TPJ. Cross-brain general linear modelling (xGLM) 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 INS 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 INS as a marker of mutual prediction during communicative social interaction.