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Previous research has shown that extended exposure to delayed reinforcement results in less impulsive choice in a subsequent delay-discounting task. Some work also suggests the opposite effect: extended exposure to immediate reinforcement may result in more impulsive choice behavior in a subsequent delay-discounting task. Understanding the impact that learning histories have on impulsive choice is important and clinically relevant because of the relationship between a strong preference for smaller-sooner over larger-later reinforcement (i.e., impulsive choice) and a myriad of other problematic health behaviors, such as substance misuse. In the present experiment, we exposed 24 rats to an immediate reinforcement intervention and 24 rats to a maturation/handle control group, followed immediately by a delay-discounting task. The procedure was designed as a systematic replication that accounted for several limitations from recent similar work. Results indicated that exposure to immediate reinforcement modestly increased impulsive choice in the delay-discounting task, but the effect was not overwhelming. These findings are consistent with previous work and have implications for understanding how experience-based interventions may affect clinically relevant impulsive choice. [ABSTRACT FROM AUTHOR]

Rodent models are commonly used in behavioral research because they offer increased experimental control and findings often generalizable to humans. However, one possible dilemma is that rodents are primarily nocturnal and research tasks often disrupt their light, rest phase. The present study used a within-subjects design to investigate possible effects of light-dark phase on delay discounting, motor coordination, open field, and elevated-plus maze behavior in Wistar rats. Rats spent significantly more time in the closed arms of the elevated plus maze when tested during the light, rest phase compared to the dark, active phase. There were no differences in motor coordination or delay discounting during the two phases. These results suggest possible important differences in certain behavioral tasks when testing in the light, rest versus dark, active phase for rats—researchers should be aware of these possible differences when planning and conducting experiments and when comparing research findings across laboratories. [ABSTRACT FROM AUTHOR]