Impact of Light–Dark Phase on Delay Discounting Behavior in Rats

Abstract

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.