Inflammatory pain modifies reward preferences from larger delayed to smaller immediate rewards in male rats

Self-control underlies goal-directed behavior in both humans and rodents. The ability to balance immediate and delayed gratification is essential for fine-tuning decision-making processes to achieve optimal rewards. Although delayed gratification has been extensively studied using human neuropsychological assessments, brain imaging techniques, and preclinical research, the impact of chronic pain on these processes remains poorly understood. In this study, we successfully trained male rats to perform a custom delayed gratification task (DGt) to evaluate time-reward gratification associations. The task required rats to choose between two levers associated with distinct schedules of reward delivery and magnitude. Behavioral performance was assessed within subjects following the induction of inflammatory chronic pain using the complete Freund's adjuvant (CFA) model. Our findings revealed that CFA-treated rats developed mechanical allodynia and demonstrated a strong preference for small and immediate rewards. In contrast, saline-treated control rats exhibited a more balanced choice profile, indicative of intact self-control. Collectively, these results offer novel insights into how chronic inflammatory pain disrupts time-reward preferences and impairs self-control mechanisms.