Mécanismes neurocomputationnels sous-tendant les conséquences différentielles du stress sur l'apprentissage social au cours d' interactions compétitives et coopératives

Overview & Synopsis

Although stress has been demonstrated to affect social interaction behaviors, the causal effect of stress on the neurocomputational mechanisms underlying social learning through dynamic interactions remains unknown. In this dissertation, combining reinforcement learning models and model-based functional magnetic resonance imaging (fMRI), we investigated how acute stress impacts social learning through dynamic competitive and cooperative interactions in humans. Furthermore, we also explored individual differences in the above stress effect. Specifically, we aimed to answer two questions: 1) When participants learn the social ranks of their opponents/teammates and adjust their choice behaviors accordingly during dynamic competitive/cooperative interactions, how does acute stress affect these two kinds of learning processes at the behavioral, computational, and brain levels? (Chapter 2)? 2) How does trait competitiveness impact the above effect of acute stress on social rank learning (Chapter 3)?We found that: 1) When learning ranks of opponents by competition, acute stress reduced choices of the strongest (high ranking) opponents who would potentially inflict more defeats, and enhanced choices of the weakest opponents against whom more victories would be expected. When learning the strength of teammates by cooperation, acute stress reduced the choice of the strongest partner who should bring more collective victories. Computational modeling revealed the mechanisms underlying such differential effects of stress on social learning via competition and cooperation. Stress played an adaptive effect in the competitive task, increasing the learning rates for defeats. At the brain system level, acute stress strengthened the prediction error signals in the striatum when learning by competition but reduced them when learning by cooperation. 2) Individual differences in trait competitiveness modulated the effect of stress on outcome representations, and the prediction error signals in the striatum and medial prefrontal cortex. Our findings reveal differential effects of acute stress on the neurocomputations engaged in learning by competition and cooperation, modulated by trait competitiveness.In summary, this thesis characterizes the effects of acute stress on neurocomputational mechanisms underlying social learning through different interaction contexts and individuals with different levels of trait competitiveness.