Learning: Not Just the Facts, Ma'am, but the Counterfactuals as Well

Our brains allow us to consider rewards and other scenarios that could have happened but did not. Such counterfactual outcomes can influence our choices and hasten learning. A series of recent studies has begun to untangle the neural circuitry responsible for monitoring counterfactual outcomes. Here, we summarize several recent complementary discoveries, including a new article in the current issue of PLoS Biology. Neurons in several brain areas that process directly experienced rewards respond to counterfactual information about rewards as well. Among these brain regions, the frontal pole appears to be most specialized, and carries a decision variable representing the value of the best alternative option. Together, these findings suggest that counterfactual learning and thinking build upon scaffolding circuits that evolved to learn from direct experience.