Psilocybin increases optimistic engagement over time: computational modelling of behaviour in rats.

Psilocybin treatment in rats performing a reversal learning task led to more rewards through increased task engagement, driven by changes in forgetting rates and reduced loss aversion. Computational modeling suggests psilocybin may induce an optimism bias by altering how beliefs are updated, which could have implications for clinical conditions marked by pessimism.

Study at a glance

Abstract

Psilocybin has shown promise as a novel pharmacological intervention for treatment of depression, where post-acute effects of psilocybin treatment have been associated with increased positive mood and decreased pessimism. Although psilocybin is proving to be effective in clinical trials for treatment of psychiatric disorders, the information processing mechanisms affected by psilocybin are not well understood. Here, we fit active inference and reinforcement learning computational models to a novel two-armed bandit reversal learning task capable of capturing engagement behaviour in rats. The model revealed that after receiving psilocybin, rats achieve more rewards through increased task engagement, mediated by modification of forgetting rates and reduced loss aversion. These findings suggest that psilocybin may afford an optimism bias that arises through altered belief updating, with translational potential for clinical populations characterised by lack of optimism.