Learning from imagined experiences via an endogenous prediction error.

Experiences shape preferences. This is particularly the case when they deviate from our expectations and thus elicit prediction errors. Here we show that prediction errors do not only occur in response to actual events - they also arise endogenously in response to merely imagined events. Specifically, people repeatedly chose between different acquaintances and then imagined interacting with them. Our results show that they acquired a preference for acquaintances with whom they had pictured unexpectedly pleasant events. This learning can best be accounted for by a computational model that calculates prediction errors based on these rewarding experiences. Using functional MRI, we show that the prediction error is mediated via striatal activity. This activity, in turn, seems to update preferences about the individuals by updating their cortical representations. Our findings demonstrate that imaginings can violate our own expectations and thus drive endogenous learning by coopting a neural system that implements reinforcement learning.