Distinct electrophysiological correlates between expected reward and risk processing

Expected reward and risk (reward variance) are two fundamental parameters in decision making, which may be encoded by distinct functional brain networks during the anticipatory phase of reward processing. However, whether and how anticipatory reward and risk processing are dissociable in terms of temporal dynamics remain ambiguous. The current event-related potential (ERP) study addressed this issue in a card-guessing task where participants were presented sequentially two cards from a deck of nine (numbered 1 through 9) and were instructed to bet whether the second card was higher or lower than the first one. Expected reward and risk were manipulated orthogonally (in an uncorrelated way) over a full range of reward probabilities (every 12.5% from 0% to 100%). We focused on three anticipatory ERP components: the cue-related reward positivity (cue-RewP), the cue-related P3 (cue-P3), and the stimulus-preceding negativity (SPN). During the period after presentation of the first card, the cue-RewP was sensitive to expected reward instead of risk, whereas the cue-P3 was mainly sensitive to risk and to a lesser extent to expected reward. During the waiting period for the second card, the SPN was sensitive to expected reward but not to risk. Our findings indicate a partial neural dissociation between expected reward and risk in the anticipatory phase of reward processing.