Using sign tracking to experimentally increase self-control in rats

Impulsive choice describes a preference for a smaller-sooner reward (SSR) over a larger-later reward (LLR). A large body of research has examined different procedures for decreasing impulsive choice in nonhuman subjects. One limitation of these procedures is the extensive training duration required to achieve the desired results. To address this limitation, the current experiment examined the effects of a brief course of Pavlovian training, designed to establish a conditioned stimulus (CS) that could be strategically used to encourage LLR choices. Forty male Long-Evans rats were randomly assigned to appetitive Pavlovian or unpaired training. A lever insertion signaled an upcoming unconditioned stimulus (i.e., food presentation) for Pavlovian rats and it acquired CS properties. The lever was uncorrelated with the US in the unpaired group, and it did not acquire CS properties. In the subsequent impulsive-choice assessment, the lever from the training phase served as the lever rats pressed to choose the LLR. After an LLR choice, the lever remained in the chamber during the delay to the LLR, just as the SSR lever remained in the chamber until that reward was delivered. Pavlovian-trained rats sign tracked toward the lever CS and made significantly fewer impulsive choices than did rats in the unpaired group.