COSTS AND BENEFITS OF ACTING TOGETHER: A NON-HUMAN PRIMATE MODEL OF COOPERATIVE DECISION-MAKING

Cooperation is a crucial aspect of social behavior, allowing individuals to achieve goals unattainable alone. However, collective actions require costly inter-individual coordination, making continuous cost-benefit evaluation essential before engaging in cooperation. Non-human primate models can help uncover the evolutionary foundations of human cooperation and its underlying neural mechanisms. To this aim, we developed a novel paradigm to analyze the dyadic behavior of two macaques, who took turns in choosing between individual and cooperative actions to obtain variable rewards. Each monkey used a joystick to guide a cursor toward one of two targets, each indicating both the reward magnitude and the action type (i.e. ‘solo action’ or ‘joint action’) required to obtain their payoff. We first observed a linear improvement in dyadic performance with the expected reward magnitude. Although macaques tended to prefer individual actions, they selected to act jointly under favorable payoff conditions, indicating that voluntary cooperation in macaques can emerge as a reward-driven process. Logistic models of their choices revealed the subjective cost monkeys assigned to cooperation, which was consistent across subjects. Nonetheless, the gain rate across different sessions increased over time, suggesting that macaques possess the cognitive ability to optimize their dyadic strategies, by estimating not only the coordination costs but also the benefits of cooperation. We observed a progressive reduction in the subjective cost assigned to joint action, which was not directly dependent on performance improvements. Our findings suggest that non-human primates can weigh the costs and benefits of cooperation, highlighting their ability to dynamically adjust social strategies based on reward contingencies.