Dissociable contributions of the ventral hippocampus and orbitofrontal cortex to decision-making with a delayed or uncertain outcome.

In this study, we examined how risk and delay influence rats' decision-making, and the role of the ventral hippocampus (VHC) and orbitofrontal cortex (OFC) in the valuation of these two factors. We used a touchscreen testing method in which rats with VHC lesions, OFC lesions and sham control surgery made choices in two decision-making tasks. In the delay discounting task, rats chose between two visual stimuli, one of which indicated a small, immediate reward, and the other of which indicated a large, delayed reward. In the probability discounting task, two stimuli indicated, instead, a small, certain reward or a large, uncertain reward. The two lesion groups showed a double dissociation with respect to the two tasks. Rats with VHC lesions were intolerant of delay, and were strongly biased towards the small, immediate reward. However, the same rats were indistinguishable from sham controls in the probability discounting task. The opposite pattern was observed for rats with OFC lesions; they performed normally in the delay discounting task, but showed a reduced tolerance for uncertainty as compared with sham-operated controls. These data support the conclusion that the VHC and OFC contribute differentially to decision-making that involves delayed or uncertain outcomes. This provides a means for understanding the neural basis of a range of neurological and psychiatric patients who show impaired decision-making and executive dysfunction.