Naturally occurring impulsive choice has been found to positively predict alcohol consumption in rats. However, the extent to which experimental manipulation of impulsive choice may modify alcohol consumption remains unclear. In the present study, we sought to: (a) train low levels of impulsive choice in rats using early, prolonged exposure to reward delay, and (b) determine the effects of this manipulation on subsequent alcohol consumption. During a prolonged training regimen, three groups of male, adolescent Long-Evans rats (21-22 days old at intake) responded on a single lever for food rewards delivered after either a progressively increasing delay, a fixed delay, or no delay. Post-tests of impulsive choice were conducted, as was an evaluation of alcohol consumption using a limited-access, two-bottle test. Following delay-exposure training, both groups of delay-exposed rats made significantly fewer impulsive choices than did rats in the no-delay group. In addition, fixed-delay rats consumed significantly more alcohol during daily, 30-min sessions than no-delay rats. Possible mechanisms of these effects are discussed, as is the significance of these findings to nonhuman models of addiction.

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Delay discounting (the devaluation of delayed rewards) has been studied extensively using animal models with psychophysical adjustment procedures. Similar procedures have been developed to assess delay discounting in humans and these procedures most often use hypothetical rewards and delays. The Experiential Discounting Task (EDT) was developed to assess human delay discounting using real rewards and delays. In the present study we examined the test-retest reliability and construct validity of the EDT. Construct validity was evaluated by comparing it to a standard delay discounting task. The EDT had poor test-retest reliability and discounting rates obtained with this task were uncorrelated with those obtained in the standard delay discounting task. Area under the EDT discounting curve was negatively correlated with scores on a measure of boredom proneness (i.e., individuals prone to boredom more steeply discounted delayed money in the EDT). This correlation may underlie previous reports that discounting in the EDT is correlated with addictions, as some evidence suggests boredom proneness is correlated with gambling, cigarette smoking, alcohol consumption, and sensation-seeking. Boredom proneness scores were correlated with no other measure of discounting. These findings suggest the EDT measures a different construct than that measured by traditional delay discounting tasks.

Discounting is a useful framework for understanding choice involving a range of delayed and probabilistic outcomes (e.g., money, food, drugs), but relatively few studies have examined how people discount other commodities (e.g., entertainment, sex). Using a novel discounting task, where the length of a line represented the value of an outcome and was adjusted using a staircase procedure, we replicated previous findings showing that individuals discount delayed and probabilistic outcomes in a manner well described by a hyperbola-like function. In addition, we found strong positive correlations between discounting rates of delayed, but not probabilistic, outcomes. This suggests that discounting of delayed outcomes may be relatively predictable across outcome types but that discounting of probabilistic outcomes may depend more on specific contexts. The generality of delay discounting and potential context dependence of probability discounting may provide important information regarding factors contributing to choice behavior.

In both humans and nonhumans, prior research demonstrates increased preference for larger‐later over smaller‐sooner rewards when rewards are bundled together in a series (i.e., when an operant choice produces multiple discrete reward deliveries, as opposed to only a single delivery). These findings can be predicted using a traditional hyperbolic delay‐discounting model. The present study was designed to examine the parametric effects of the size of the reward bundle on larger‐later reward preference in male rats. During a reward‐bundling phase, rats were exposed to bundle‐sizes of either 1 (i.e., no bundling), 3, or 9 rewards. Rats in the Bundle‐size 9 group showed significantly greater larger‐later reward preference across a range of delays (0‐17.5 s) than rats in any other group, but no other significant differences in choice were observed between groups. In addition, when choice for unbundled rewards was assessed following the reward‐bundling phase, rats in the Bundle‐size 9 group showed a significant increase in larger‐later reward preference (compared to a pre‐test). Obtained data from the reward‐bundling phase are compared to model‐predicted data, and potential mechanisms of the observed increase in self‐control for unbundled rewards are discussed.

Evaluating the effects of presession drug administration on intertemporal choice in nonhumans is a useful approach for identifying compounds that promote impulsive behavior in clinical populations, such as those prescribed the dopamine agonist pramipexole (PPX). Based on the results of previous studies, it is unclear whether PPX increases rats’ impulsive choice or attenuates aspects of stimulus control. The present study was designed to experimentally isolate behavioral processes fundamental to intertemporal choice and challenge them pharmacologically with PPX administration. In Experiment 1, the hypothesis that PPX increases impulsive choice as a result of enhanced sensitivity to reinforcer delays was tested and disconfirmed. That is, acute PPX diminished delay sensitivity in a manner consistent with disruption of stimulus control whereas repeated PPX had no effect on delay sensitivity. Experiments 2 and 3 elaborated upon this finding by examining the effects of repeated PPX on rats’ discrimination of response–reinforcer contingencies and reinforcer amounts, respectively. Accuracy of both discriminations was reduced by PPX. Collectively these results provide no support for past studies that have suggested PPX increases impulsive choice. Instead, PPX impairs stimulus control over choice behavior. The behavioral approach adopted herein could be profitably integrated with genetic and other biobehavioral models to advance our understanding of impulsive behavior associated with drug administration.