A nonlinear association between chronic stress and instrumental reward learning under Pavlovian conflict: Behavioural and computational evidence

Chronic stress, arising from prolonged exposure to unpredictable challenges, is common in everyday life and may alter cognitive processes. However, few human studies have empirically examined the association between chronic stress and reward learning, which is critical for navigating uncertain environments. This study addressed this gap by examining whether chronic stress is associated with the influence of Pavlovian bias on instrumental reward learning. A total of 111 healthy young adults participated in the study, completing an orthogonalised go/no-go task and a self-reported measure of chronic stress. Participants' chronic stress levels exhibited an inverted-U-shaped relationship with learning accuracy in the Pavlovian-conflict condition, particularly in the reward domain. Between-group analyses supported this pattern, with the moderate-stress group performing best in the Pavlovian-conflict condition of the reward domain. Computational modelling results further revealed that, compared to the moderate-stress group, the low- and high-stress groups exhibited greater reward-related Pavlovian bias and the high-stress group exhibited blunted reward sensitivity. Together, these findings suggest that the association between chronic stress and reward learning may be nonlinear. Moderate levels of chronic stress may be associated with relatively better performance in specific reward-learning contexts.