Impulsive choice and pre-exposure to delays: iv. effects of delay- and immediacy-exposure training relative to maturational changes in impulsivity

Abstract

Impulsive choice describes preference for smaller, sooner rewards over larger, later rewards. Excessive delay discounting (i.e., rapid devaluation of delayed rewards) underlies some impulsive choices, and is observed in many maladaptive behaviors (e.g., substance abuse, gambling). Interventions designed to reduce delay discounting may provide therapeutic gains. One such intervention provides rats with extended training with delayed reinforcers. When compared to a group given extended training with immediate reinforcers, delay-exposed rats make significantly fewer impulsive choices. To what extent is this difference due to delay-exposure training shifting preference toward self-control or immediacy-exposure training (the putative control group) shifting preference toward impulsivity? The current study compared the effects of delay- and immediacy-exposure training to a no-training control group and evaluated within-subject changes in impulsive choice across 51 male Wistar rats. Delay-exposed rats made significantly fewer impulsive choices than immediacy-exposed and control rats. Between-group differences in impulsive choice were not observed in the latter two groups. While delay-exposed rats showed large, significant pre- to posttraining reductions in impulsive choice, immediacy-exposed and control rats showed small reductions in impulsive choice. These results suggest that extended training with delayed reinforcers reduces impulsive choice, and that extended training with immediate reinforcers does not increase impulsive choice.

Keywords: delay discounting; delay-exposure training; impulsive choice; lever press; rat.