Reward prediction errors induce risk-seeking

Abstract Reinforcement learning theories propose that humans choose based on the estimated values of available options, and that they learn from rewards by reducing the difference between the experienced and expected value. In the brain, such prediction errors are broadcasted by dopamine. However, choices are not only influenced by expected value, but also by risk. Like reinforcement learning, risk preferences are modulated by dopamine: enhanced dopamine levels induce risk-seeking. Learning and risk preferences have so far been studied independently, even though it is commonly assumed that they are (partly) regulated by the same neurotransmitter. Here, we use a novel learning task to look for prediction-error induced risk-seeking in human behavior and pupil responses. We find that prediction errors are positively correlated with risk-preferences in imminent choices. Physiologically, this effect is indexed by pupil dilation: only participants whose pupil response indicates that they experienced the prediction error also show the behavioral effect.