Reducing impulsive choice VII: effects of duration of delay-exposure training

Abbreviated fixed-interval interventions promote self-control in rats

Impulsive choice, defined as choices of a smaller-sooner reward over a larger-later reward, can be reduced by time-based interventions that expose rats to delayed rewards. These interventions improve temporal processing concurrent with reducing impulsive choice. Exposure to delayed reinforcement has produced improvements in self-control after 30 sessions of intervention exposure (Renda et al., 2021). Experiment 1 of the present study used a pre-/post-test design to investigate a range of intervention exposures (6, 15, 30, and 45 sessions), including shorter exposures that have not previously been examined. Peak-interval timing was also assessed to determine whether different intervention exposures would improve temporal processing. All intervention exposures, including the abbreviated intervention, reduced impulsive choice, and improved temporal processing. Experiment 2 showed that the 6-session intervention improved self-control relative to a no-delay control, further strengthening the proposal that an abbreviated intervention may be sufficient to reduce impulsive choice. Moreover, improvements in peak-interval timing were observed in groups receiving a pre-intervention impulsive choice assessment, suggesting that exposure to the impulsive choice task may improve temporal processing.

Mechanisms of impulsive choice: Experiments to explore and models to map the empirical terrain

Impulsive choice is preference for a smaller-sooner (SS) outcome over a larger-later (LL) outcome when LL choices result in greater reinforcement maximization. Delay discounting is a model of impulsive choice that describes the decaying value of a reinforcer over time, with impulsive choice evident when the empirical choice-delay function is steep. Steep discounting is correlated with multiple diseases and disorders. Thus, understanding the processes underlying impulsive choice is a popular topic for investigation. Experimental research has explored the conditions that moderate impulsive choice, and quantitative models of impulsive choice have been developed that elegantly represent the underlying processes. This review spotlights experimental research in impulsive choice covering human and nonhuman animals across the domains of learning, motivation, and cognition. Contemporary models of delay discounting designed to explain the underlying mechanisms of impulsive choice are discussed. These models focus on potential candidate mechanisms, which include perception, delay and/or reinforcer sensitivity, reinforcement maximization, motivation, and cognitive systems. Although the models collectively explain multiple mechanistic phenomena, there are several cognitive processes, such as attention and working memory, that are overlooked. Future research and model development should focus on bridging the gap between quantitative models and empirical phenomena.

Temporal expectations in delay of gratification

We examined how temporal expectations influence preference reversals in a delay of gratification task for rats based on a hypothesis of Rachlin (2000), who suggested that preference for a larger-later reward may shift in favor of a smaller-immediate reward as a result of changes in when that larger reward is expected. To explore Rachlin's hypothesis, we preexposed two groups of rats to the delays associated with a larger-later reinforcer from a delay of gratification task. One group experienced the delays as a function of their choices in an intertemporal choice task and the other group experienced delays yoked from the first group (independent of their behavior) in an exposure training procedure. In addition, we included a third group of rats that were not exposed to delays during preexposure training as a comparison to the other two groups. Overall, the two groups of rats that experienced delays during preexposure training tended to make fewer defection responses than the comparison group during the delay of gratification task. Consistent with Rachlin's hypothesis, our results suggest that temporal learning may influence preference reversals in a delay of gratification task, providing a number of future directions for research in this area.

Effects of immediate-reinforcement training on delay discounting behavior in rats

Chronic exposure to delayed reinforcement has been shown to increase choice for larger, later reinforcement in a subsequent delay discounting task. In the 3 experiments presented in this paper, the opposite was tested: effects of chronic exposure to immediate reinforcement on choice in a subsequent delay discounting task. In Experiment 1, larger, later reinforcement choice was significantly reduced as a result of exposure to immediate reinforcement, compared to a maturation/handle control group, in experienced, male Lewis rats. In Experiment 2, with naive male and female Wistar rats, and Experiment 3, with naïve male Long Evans rats, the impact of exposure to immediate reinforcement was less robust, but directionally consistent with results from Experiment 1. These results align with some previous work reporting that exposure to immediate reinforcement may decrease choice for larger, later reinforcement in a delay discounting task, and/or blunt maturational increases in choice for larger, later reinforcement. These findings have implications for future research investigating experience-based interventions to manipulate delay discounting behavior. They also have clinical implications for understanding and treating disorders involving maladaptive choice.