Brain regions involved in the learning and application of reward rules in a two-deck gambling task

Decision-making involves the ability to choose between competing actions that are associated with uncertain benefits and penalties. The Iowa Gambling Task (IGT), which mimics real-life decision-making, involves learning a reward-punishment rule over multiple trials. Patients with damage to ventromedial prefrontal cortex (VMPFC) show deficits learning these rules, although this performance deficit is not exclusively associated with VMPFC damage. In this study, we used functional Magnetic Resonance Imaging (fMRI) to study the roles of prefrontal cortex regions involved in rule learning and rule application in healthy adults using an adapted version of the Iowa Gambling Task. Participants (N=20) were asked to infer rules over series of 16 trials in a two-deck card game. Rewards were given on each trial and punishment was unpredictable. For half of the series, those decks that gave high rewards were also better decks in the long run. For the other half of the series, the decks that gave low rewards were better decks in the long run. Behaviorally, participants started to differentiate between advantageous and disadvantageous decks after approximately four/six trials, and learning occurred faster for high-reward decks. Lateral PFC (lat-PFC) and Anterior Cingulate Coretex (ACC)/pre-supplementary motor area (pre-SMA) were most active for early decisions, whereas medial orbital frontal cortex (med-OFC) was most active for decisions made later in the series. These results suggest that lat-PFC and ACC/pre-SMA are important for directing behavior towards long-term goals, whereas med-OFC represents reward values towards which behavior should be directed.