Variations in discount rates are associated with differences in the ability to imagine future rewards
Behavioral studies have shown that there is considerable variation across individuals on their ability to postpone gratification in order to obtain larger delayed rewards. It has been hypothesized that some of this variation might be due to differences on the ability to represent the value of future rewards. We tested this hypothesis using human functional neuroimaging while participants performed two different tasks: an intertemporal monetary choice (ITC) task where they made binary choices between a small immediate amount of money and larger delayed payments, and a visualization task in which they consumed or imagined consuming appetitive liquid rewards. Consistent with previous studies, we found that the subjective value of the monetary offers was encoded in ventral medial prefrontal cortex (vmPFC) during the ITC task. We also found a common area of left ventrolateral prefrontal cortex (vlPFC) that exhibited a pattern of activity consistent with the main hypothesis. During ITC, this region exhibited stronger activation in more difficult trials (where there is a conflict between the immediate and delayed values of the rewards), as well as increased functional connectivity with the area of vmPFC involved in valuation. During the visualization task, the same region showed stronger activation during imagining than consumption trials, and it also exhibited increased functional connectivity with vmPFC. Moreover, more patient participants exhibited enhanced responses in vmPFC during the imagination component of the visualization task. Together, these data suggest that the left vlPFC plays a critical role in computing the value of delayed rewards during decision-making.