Dopamine dynamics promote cooperative behavior not just the rewards accompanying cooperation

Cooperation requires precise spatiotemporal coordination, whereas previous studies have largely focused on decision-making neural circuits. We combined the genetically encoded dopamine (DA) sensor GRAB_DA3m with a cooperative nose-poke task to monitor DA dynamics in the medial shell of the nucleus accumbens (NAcmedSh) during cooperative learning and maintenance in mice. Fiber photometry revealed that cooperation-related DA transients gradually increased during learning and strongly correlated with cooperative success. In non-cooperative social and independent controls, DA signals were associated with reward delivery. Extinction and delayed-reward experiments dissociated cooperation-related DA activity from external rewards. Reversal experiments showed that this representation remained stable after task switching. Furthermore, local microinjection of the D1 receptor antagonist SCH-23390 (0.05 μg/side) into the NAc selectively reduced cooperative success without affecting feeding motivation or locomotor activity. These findings indicate that NAc DA signaling represents the intrinsic value of cooperation beyond external reward, with D1R-dependent phasic DA contributing to its maintenance.