Rats pursue food and leisure following the same rational principles

Animals in the wild must balance multiple, potentially mutually-exclusive goals simultaneously in order to survive. Yet laboratory tests of decision making often investigate how animals optimize their behavior to achieve a single, well-defined goal, which is often a nutritive reward. Thus, how animals solve multi-objective optimization problems is not well understood. Here, we devised an ethologically-inspired decision making task to examine how rats balance the pursuit of food and non-food reinforcement. Rats performed a free-choice patch-foraging task, in which they could earn food in one location (food patch) or interact with a rodent play structure in a different location (toy patch). The cost of switching between patches was manipulated by requiring rats to endure a long or short "travel time" penalty during which they were not able to access either patch. Rats devoted a considerable amount of their limited foraging time to patches of both types, showing a small but significant preference for food patches. In accordance with theoretical models of foraging, when the cost of switching patches was high rats chose longer stay durations in both types of patches, suggesting that similar rational principles guided their pursuit of food and non-food rewards. Examining the within-session dynamics of time allocation revealed that rats showed an early preference for spending time in toy patches that reversed over the course of the session. Satiety manipulations demonstrated that patch residence time decisions were under goal-directed control, and responsive to current needs and recent consumption. These results validate a naturalistic approach to testing decision making in rats over a range of food and non-food goods. Key words: Patch foraging, decision making, multi-objective optimization, play, leisure Significance StatementThe mechanisms by which animals trade off competing goals remain poorly understood. Here, we investigated whether rats use rational decision-making strategies to balance essential needs with non-essential pursuits like leisure by letting rats choose between earning food and engaging with a play structure. Rats performing a free-choice patch-foraging task adjusted their behavior based on opportunity costs, staying longer in patches when switching costs were high, in accordance with models of optimal foraging. Rats allocated significant time to toy patches, even at the expense of food rewards, underscoring the intrinsic value of non-food reinforcers. These results validate a naturalistic approach for studying tradeoffs between qualitatively-different rewards, and advance our understanding of multi-goal optimization in the context of a naturalistic decision problem.