Effects of THC on Behavioral Measures of Impulsivity in Humans

Abstract

This study investigated the acute effects of D 9 -tetrahydrocannabinol (THC) on four behavioral measures of impulsivity in recreational marijuana users. Although impulsive behavior has been studied using several different measures of impulsivity, few studies have utilized more than one of these measures on a single cohort. In this study, 37 healthy men and women participated in three sessions, in which they received capsules containing placebo, 7.5, or 15 mg THC in randomized order under double-blind conditions. Subjects were tested on the following four tasks: the Stop task, which measures the ability to inhibit a prepotent motor response; a Go/no-go task; a Delay discounting task, which measures the value of delayed or uncertain reinforcers; and a time estimation task, which measures alterations in time perception through a time reproduction procedure. Subjects also completed mood questionnaires and general measures of performance. THC produced its expected effects on subjective measures including increases in ARCI euphoria and marijuana scales. THC increased impulsive responding on the Stop task but did not affect performance on either the Go/no-go or Delay or Probability discounting tasks. On the time reproduction task, THC increased estimates of the duration of short intervals while not affecting estimates of longer intervals. There were no significant correlations between the four tasks either before or after drug administration. These results suggest that THC may increase certain forms of impulsive behavior while not affecting other impulsive behaviors. The dissociations between the four measures of impulsivity suggest that impulsivity is an assemblage of distinct components rather than a unitary process.

Fractionating Impulsivity: Contrasting Effects of Central 5-HT Depletion on Different Measures of Impulsive Behavior

“…These data provide direct preclinical evidence for the hypothesis that impulsivity is a nonunitary concept, which is not underpinned by a single neurobiological mechanism (Evenden, 1999;Moeller et al, 2001). In support of this suggestion, little correlation has been found between different measures of impulsivity in normal human volunteers (McDonald et al, 2003), and although clinical studies often use the Barratt Impulsiveness Scale (BIS) as an overall measure of 'trait impulsivity', factor analysis reveals that the items within this scale cluster into three independent factors (Patton et al, 1995). In a recent study using human volunteers, errors of commission on a continuous performance test (a potential measure of impulsive action analogous to the 5CSRT and 'one-choice' tasks) were strongly correlated with BIS scores, whereas performance on a delay-discounting task showed only a moderate correlation with this questionnaire measure (Swann et al, 2002).…”

“…Furthermore, the increase in impulsive choice seen in delay-discounting tasks in rats following serotonergic lesions has not always been observed (Winstanley et al, 2003), nor found to be permanent (Bizot et al, 1999). Recently, a battery of tasks was used to measure impulsive behavior in a group of human volunteers, and no correlation was observed between the different indices of impulse control (McDonald et al, 2003), strongly suggesting that impulsivity is not underpinned by a unitary process. One of the aims of this investigation was therefore to apply a similar approach to the study of impulsivity in rodents, specifically by training the same cohort of animals on a variety of different tests of impulsive behavior.…”

Relapse to smoking during unaided cessation: clinical, cognitive and motivational predictors

“…McDonald et al, 2003) and is difficult to reconcile straightforwardly with the theoretical premise that they are all similarly influenced by abnormalities of functioning in shared mesocorticolimbic brain circuitry. Whilst differences between tasks in terms of non-shared processes, content, or procedural details will tend to weaken associations, the lack of evidence for even modest interrelationships suggests either that the processes putatively tapped by the tasks do not depend on shared neuronal mechanisms or that the tasks are not, after all, sensitive to those processes.…”

Impulsive choice and environmental enrichment: Effects of d-amphetamine and methylphenidate

“…In humans, acute administration of methylphenidate [67] or d-amphetamine [20] decreases impulsive choice; however, discounting does not change with administration of alcohol [59,74], diazepam [71], or Δ 9 -tetrahydrocannabinol [53]. However, since these studies were conducted in individuals with prior drug experience, preclinical research may be better suited to determine the acute effects of drugs on impulsive choice.…”