Separate Neural Systems Value Immediate and Delayed Monetary Rewards

TLDR

When humans choose between rewards at different times, the value of each option is discounted by its delay. Using fMRI, we examined neural correlates of time discounting while subjects chose between monetary rewards varying in delivery delay. We found that limbic midbrain dopamine and paralimbic cortex activity preferentially marked immediate rewards, while lateral prefrontal and posterior parietal regions were engaged uniformly across delays, and the relative balance of these systems predicted selection of longer‑term options.

Abstract

When humans are offered the choice between rewards available at different points in time, the relative values of the options are discounted according to their expected delays until delivery. Using functional magnetic resonance imaging, we examined the neural correlates of time discounting while subjects made a series of choices between monetary reward options that varied by delay to delivery. We demonstrate that two separate systems are involved in such decisions. Parts of the limbic system associated with the midbrain dopamine system, including paralimbic cortex, are preferentially activated by decisions involving immediately available rewards. In contrast, regions of the lateral prefrontal cortex and posterior parietal cortex are engaged uniformly by intertemporal choices irrespective of delay. Furthermore, the relative engagement of the two systems is directly associated with subjects' choices, with greater relative fronto-parietal activity when subjects choose longer term options.