Reducing impulsive choice: VI. Delay-exposure training reduces aversion to delay-signaling stimuli.

Delay-exposure (DE) training consistently and robustly reduces impulsive choice in rats, but the behavioral mechanisms behind this effect are not yet understood. The present study evaluated if DE training works by mitigating aversion to delay-signaling stimuli-those encountered when rats chose the larger-later reward in impulsive choice assessments. Fifty-seven rats were randomly assigned to 120 days of training with delayed reinforcement, training with immediate reinforcement (IE), or to a no-training Control group. Consistent with prior experiments, DE rats made significantly fewer impulsive choices than IE or Control rats. Subsequently, in a separate assessment of delay aversion, rats were given the opportunity to press a lever to temporarily escape from stimuli correlated with long or short time-intervals to food. When these escape opportunities terminated delay-signaling stimuli in the impulsive-choice task, DE rats escaped significantly less than IE and Control rats. When escapes terminated FI-signaling stimuli (a procedure in which there is no response-reinforcer delay), the difference only approached significance. These results support the hypothesis that DE training reduces impulsive choice, in part, by reducing aversion to delay-signaling stimuli. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

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

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.

How suboptimal is suboptimal choice?

In a frequently used suboptimal-choice procedure pigeons choose between an alternative that delivers three food pellets with p = 1.0 and an alternative that delivers ten pellets with p = 0.2. Because pigeons reliably choose the probabilistic (suboptimal) alternative, the procedure has been proposed as a nonhuman analog of human gambling. The present experiments were conducted to evaluate two potential threats to the validity of this procedure. Experiments 1 and 2 evaluated if pigeons obtained food at a lower unit price (i.e., pecks per pellet) on the suboptimal alternative than on the optimal alternative. When pigeons worked under this suboptimal procedure they all preferred the suboptimal alternative despite some pigeons paying a higher price for food on that alternative. In Experiment 2, when the unit price ratio more closely approximated the inverse of the expected value ratio, pigeons continued to prefer the suboptimal alternative despite its economic suboptimality. Experiment 3 evaluated if, in accord with the string-theory of gambling, the valuation of the suboptimal alternative was increased when pigeons misattributed a subset of the suboptimal no-food trials to the optimal alternative. When trial sequences were arranged to minimize these possible attribution errors, pigeons still preferred the suboptimal alternative. These data remove two threats to the validity of the suboptimal choice procedure; threats that would have suggested that suboptimal choice reflects economic maximization.

Impulsive choice, alcohol consumption, and pre-exposure to delayed rewards: II. Potential mechanisms.

In a prior study (Stein et al., 2013), we reported that rats pre-exposed to delayed rewards made fewer impulsive choices, but consumed more alcohol (12% wt/vol), than rats pre-exposed to immediate rewards. To understand the mechanisms that produced these findings, we again pre-exposed rats to either delayed (17.5 s; n=32) or immediate (n=30) rewards. In posttests, delay-exposed rats made significantly fewer impulsive choices at 15- and 30-s delays to a larger, later food reward than the immediacy-exposed comparison group. Behavior in an open-field test provided little evidence of differential stress exposure between groups. Further, consumption of either 12% alcohol or isocaloric sucrose in subsequent tests did not differ between groups. Because Stein et al. introduced alcohol concentration gradually (3-12%), we speculate that their group differences in 12% alcohol consumption were not determined by alcohol's pharmacological effects, but by another variable (e.g., taste) that was preserved as an artifact from lower concentrations. We conclude that pre-exposure to delayed rewards generalizes beyond the pre-exposure delay; however, this same experimental variable does not robustly influence alcohol consumption.