An improved within-session self-adjusting delay discounting procedure for the study of choice impulsivity in rats

Abstract

Rationale: Delay-discounting procedures involving choice between small immediate rewards and large delayed rewards are used to study impulsivity in rodents. Improving existing procedures may provide new insights into the neurobiological mechanisms underlying decision-making processes.

Objectives: To develop a novel delay-discounting procedure that adjusts the delay value within individual sessions based on the rat's most recent choices.

Methods: Compared to previously developed procedure, we required a more consistent demonstration of preference, five consecutive choices of the large or small reward, a criterion that is more likely to reflect deliberate choice by the animal, as opposed to two consecutive choices. In addition, delays were changed in steps of 5 s (rather than 1 s), because 5-s increments should be more easily discriminated and may produce a more distinct effect on choice. We characterized the procedure behaviorally by manipulating the duration of the session and the consecutive choice criterion, and we investigated the stability of the behavior upon interruption of training. We also characterized the procedure pharmacologically by investigating the effects of dopaminergic compounds.

Results: Our procedures allowed obtaining two complementary measures of delay discounting: (1) the percentage of choices of the delay option and (2) the mean adjusting delay, an index of the delay that animals choose more frequently. We found that our procedure rapidly establishes a baseline of choice behavior that remains stable over time and is highly sensitive to manipulations of the dopaminergic system.

Conclusions: This procedure may provide a useful tool for investigating the neurobiology of inter-temporal choice and decision-making.

Keywords: Addiction; Cognition; Decision-making; Dopamine; Intertemporal discounting; Psychostimulants.