Predicting outcomes of decisions in the brain.

When making decisions, the outcomes of different choices play an important role. Feedback is mainly processed in terms of gains and losses. It is as yet unclear whether this distinction holds for predictable as well as unpredictable outcomes. Using ERPs, the present study aimed to determine whether predictable and unpredictable outcomes are coded differently in the brain. Participants had to choose between one of two options: the certain option was always associated with a gain of 10 euro, while the uncertain option entailed a gain of 30 euro or a loss of 10 euro, with a probability of 50% each. Overall, subjects showed a clear preference for the certain option, a tendency which became more pronounced during the course of the experiment. An early ERP component, the P200, reflected the predictability of outcomes, which was critical for the subsequent decisions. The later feedback related negativity (FRN) reflected the known distinction between gains and losses, while the N500 again reflected differential processing of predictable and unpredictable outcomes. Neither FRN nor the N500 were significantly related to behaviour. Predictability appears to play a central role in outcome evaluation.