Rats Delay Gratification During a Time-Based Diminishing Returns Task

The rat is a common animal model used to uncover the neural underpinnings of decision making and their disruption in psychiatric illness. Here, we ask if rats can perform a decision-making task that assesses self-control by delayed gratification in the context of diminishing returns. In this task, rats could choose to press one of two levers. One lever was associated with a fixed delay (FD) schedule that delivered reward after a fixed time delay (10 s). The other lever was associated with a progressive delay (PD) schedule; the delay increased by a fixed amount of time (1 s) after each PD lever press. Rats were tested under two conditions: a reset condition where rats could reset the PD schedule back to its initial 0-s delay by pressing the FD lever and a no-reset condition in which resetting the PD schedule was unavailable. We found that rats adapted behavior within reset sessions by delaying gratification to obtain more reward in the long run. That is, they selected the FD lever with the longer delay to reset the PD delay back to zero prior to the equality point, thus achieving more reward over the course of the session. These results are consistent with other species, demonstrating that rats can also maximize the net rate of reward by selecting an option that is not immediately beneficial. Moreover, use of this task in rodents might provide insights into how the brain governs normal and abnormal behavior, as well as treatments that can improve self-control.