Reward Maximization Assessed Using a Sequential Patch Depletion Task in a Large Sample of Heterogeneous Stock Rats

Abstract

Choice behavior requires animals to evaluate both short- and long-term advantages and disadvantages of all potential alternatives. Impulsive choice is traditionally measured in laboratory tasks by utilizing delay discounting (DD), a paradigm that offers a choice between a smaller immediate reward, or a larger more delayed reward. This study tested a large sample of Heterogeneous Stock (HS) male (n = 896) and female (n = 898) rats, part of a larger genetic study, to investigate whether measures of reward maximization overlapped with traditional models of delay discounting via the patch depletion model using a Sequential Patch Depletion procedure. In this task, rats were offered a concurrent choice between two water “patches” and could elect to “stay” in the current patch or “leave” for an alternative patch. Staying in the current patch resulted in decreasing subsequent reward magnitudes, whereas the choice to leave a patch was followed by a delay and a resetting to the maximum reward magnitude. Based on the delay in a given session, different visit durations were necessary to obtain the maximum number of rewards. Visit duration may be analogous to an indifference point in traditional DD tasks. While differences in traditional DD measures (e.g., delay gradient) have been detected between males and females, these effects were small and inconsistent. However, when examining measures of reward maximization, females made fewer patch changes at all delays and spent more time in the patch before leaving for the alternative patch compared to males. This pattern of choice resulted in males having a higher rate of reinforcement than females. Consistent with this, there was some evidence that females deviated from the optimal more, leading to less reward. Measures of reward maximization were only weakly associated with traditional DD measures and may represent distinctive underlying processes. Taken together, females performance differed from males with regard to reward maximization that were not observed utilizing traditional measures of DD, suggesting that the patch depletion model was more sensitive to modest sex differences when compared to traditional DD measures in a large sample of HS rats.

Environmental enrichment promotes adaptive responding during tests of behavioral regulation in male heterogeneous stock rats

“… 102 . However, the present study used a sequential patch depletion (i.e., foraging) procedure, which requires the animal to make sequential choices between staying in a “patch” and leaving it for a new patch, rather than typical delay discounting procedures in which the animal has to make mutually exclusive choices between two simultaneously presented discrete alternatives 46 , 47 , 103 . One consequence of the parameters in this task (no inter-trial-interval) is that relatively delayed patch-leaving yielded more water reward during sessions.…”

“…The sequential patch depletion is a foraging task procedure described previously 46 , Fig. 6 A, Ref.…”

Environmental enrichment promotes adaptive responding during tests of behavioral regulation in male heterogeneous stock rats

“…Others have also reported an increased preference for sooner, smaller rewards over delayed, larger ones by EE rats compared to SH and isolation-reared rats (e.g., (Hellemans et al, 2005). However, the present study used a sequential patch depletion (i.e., foraging) procedure, which requires the animal to make sequential choices between staying in a "patch" and leaving it for a new patch, rather than typical delay discounting procedures in which the animal has to make mutually exclusive choices between two simultaneously presented discrete alternatives (Gancarz et al, 2023;Hayden, 2016;Richards et al, 2013). One consequence of the parameters in this task (no inter-trial-interval) is that relatively delayed patch-leaving yielded more water reward during sessions.…”