Medial frontal event-related potentials and reward prediction: do responses matter?

Medial frontal event-related potentials (ERPs) following rewarding feedback index outcome evaluation. The majority of studies examining the feedback related medial frontal negativity (MFN) employ active tasks during which participants' responses impact their feedback, however, the MFN has been elicited during passive tasks. Many of the studies examining the MFN show enhanced effects when an error in reward prediction occurs (i.e. expected rewards are not delivered). To clarify the roles of reward prediction error and active responding in producing the MFN, the current study employed a reward prediction design with active and passive task blocks. Following the presentation of a reward predictor, participants (active task) or the computer (passive task) indicated whether participants would receive the outcome associated with a stimulus presented on the left or right of the reward predictor. The MFN was largest when the trial outcome was worse than predicted and this effect was enhanced when the participant, rather than the computer, made the choice. These results show that both reward prediction error and active choice impact the neural system of outcome monitoring with the largest MFN when the individual's decision led to the negative outcome.