Distinct fNIRS Inter-Brain Coupling Patterns for Cooperation vs. Competition in a Tennis Game.

Cooperation and competition represent two fundamental modes of social interaction, yet their underlying neural mechanisms remain incompletely understood. Functional near-infrared spectroscopy (fNIRS) hyperscanning, enabling simultaneous measurement of hemodynamic activity across individuals, offers unique insights into the neural substrates underlying naturalistic interactions. Using this technique, we investigated cross-channel inter-brain coupling (IBC) between interacting individuals during cooperative and competitive play in a motion-sensing tennis game. Compared to resting-state and solo gameplay with observation, both conditions elicit significantly enhanced not only IBC between the dyads' sensorimotor regions, but also cross-regional coupling between one participant's sensorimotor cortex and the other's dorsolateral prefrontal cortex (DLPFC) as well as temporoparietal junction (TPJ), suggesting the contribution of high-order cognition networks to the observed IBC. Notably, competitive interactions produce stronger cross-reginal IBC between DLPFC and sensorimotor regions than cooperative ones, implying intensified demand of cognitive control during competition. Conversely, cooperation enhances neural coupling between teammates within their prefrontal cortices which could reflect shared goal representations. Behavioral cooperation performance is negatively correlated with the DLPFC-sensorimotor IBC. These spatially distinct patterns of condition-dependent neural coupling advance our understanding of the neural underpinning of naturalistic social interactions.