DELAY OR PROBABILITY DISCOUNTING IN A MODEL OF IMPULSIVE BEHAVIOR: EFFECT OF ALCOHOL

TLDR

The acute effects of drugs of abuse on impulsivity and self‑control are poorly understood, and discounting quantifies how reward value diminishes with delay or uncertainty. The study aimed to assess human impulsivity by measuring delay and probability discounting with a computer task. Twenty‑four healthy adults received moderate doses of ethanol (0.5 or 0.8 g/kg) or placebo, then completed a delay‑probability discounting task that presented choices between a small immediate reward and $10 delayed or probabilistic, with indifference points determined by an adjusting‑amount procedure. Results showed delay and probability discounting followed a hyperbolic function, were positively correlated within subjects, moderately correlated with impulsivity traits, and were unaffected by alcohol.

Abstract

Little is known about the acute effects of drugs of abuse on impulsivity and self‐control. In this study, impulsivity was assessed in humans using a computer task that measured delay and probability discounting. Discounting describes how much the value of a reward (or punisher) is decreased when its occurrence is either delayed or uncertain. Twenty‐four healthy adult volunteers ingested a moderate dose of ethanol (0.5 or 0.8 g/kg ethanol; n = 12 at each dose) or placebo before completing the discounting task. In the task the participants were given a series of choices between a small, immediate, certain amount of money and $10 that was either delayed (0, 2, 30, 180, or 365 days) or probabilistic (i.e., certainty of receipt was 1.0, .9, .75, .5, or .25). The point at which each individual was indifferent between the smaller immediate or certain reward and the $10 delayed or probabilistic reward was identified using an adjusting‐amount procedure. The results indicated that (a) delay and probability discounting were well described by a hyperbolic function; (b) delay and probability discounting were positively correlated within subjects; (c) delay and probability discounting were moderately correlated with personality measures of impulsivity; and (d) alcohol had no effect on discounting.