Selective involvement by the medial orbitofrontal cortex in biasing risky, but not impulsive, choice

Separate regions of the orbitofrontal cortex (OFC) have been implicated in mediating different aspects of cost-benefit decision-making in humans and animals. Anatomical and functional imaging studies indicate that the medial (mOFC) and lateral OFC may subserve dissociable functions related to reward and decision-making processes, yet the majority of studies in rodents have focused on the lateral OFC. The present study investigated the contribution of the rat mOFC to risk and delay-based decision-making, assessed with probabilistic and delay-discounting tasks. In well-trained rats, reversible inactivation of the mOFC increase a risky choice on the probabilistic discounting task, irrespective of whether the odds of obtaining a larger/risky reward decreased (100-12.5%) or increased (12.5-100%) over the course of a session. The increase in risky choice was associated with enhanced win-stay behavior, wherein rats showed an increased tendency to choose the risky option after being rewarded for the risky choice on a preceding trial. In contrast, mOFC inactivation did not alter delay discounting. These findings suggest that the mOFC plays a selective role in decisions involving reward uncertainty, mitigating the impact that larger, probabilistic rewards exert on subsequent choice behavior. This function may promote the exploration of novel options when reward contingencies change.