Stochastic decisions support optimal foraging of volatile environments, and are disrupted by anxiety.

Adolescence is a developmental period of relative volatility, where the individual experiences significant changes to their physical and social environment. The ability to adapt to the volatility of one's surroundings is an important cognitive ability, particularly while foraging, a near-ubiquitous behaviour across the animal kingdom. As adolescents experience more volatility in their surroundings, we predicted that this age group would be more adept than adults at using exploration to adjust to volatility. We employed a foraging task with a well-validated computational model to characterise the mechanisms of exploration in volatile environments, preregistering the hypothesis that adolescents (aged 16-17; N = 91) would exhibit more optimal adaptation of their learning rate to changes in environmental volatility compared with adults (aged 24+; N = 90). However, surprisingly, both adolescents and adults exhibited suboptimal adjustment of their learning rate to environmental volatility. In contrast to the learning rate, it was instead participants' stochasticity (i.e., decision variability) that better resembled the adjustment to volatility made by the optimal RL agent. Although heightened stochasticity in the volatile environment led participants to more often trial different responses that facilitated discovery of changes to the environment, we also found that anxiety impaired this adaptive ability. The finding of heightened stochasticity in volatile environments contradicts expectations that the learning rate is responsible for successful adaptation and motivates future work on the deleterious role that anxiety plays when adolescents manage periods of transition.