Δ⁹-Tetrahydrocannabinol (THC) impairs visual working memory performance: a randomized crossover trial

Area of Science:

• Neuroscience
• Psychopharmacology
• Cognitive Psychology

Background:

• Increasing legal cannabis availability necessitates understanding cognitive effects.
• Existing literature provides limited empirical support for Δ⁹-tetrahydrocannabinol (THC) impairing working memory.
• The specific cognitive mechanisms underlying potential THC-induced working memory deficits require further investigation.

Purpose of the Study:

• To quantify the effect of THC on visual working memory in a well-powered sample.
• To examine the role of mind wandering and metacognition in mediating THC's impact on working memory.
• To illustrate how insufficient sample size and task duration affect the detection of drug effects.

Main Methods:

• Two double-blind, randomized crossover experiments involving healthy adults (N=23, 23).
• Administration of oral Δ⁹-tetrahydrocannabinol (THC) (7.5 and/or 15 mg) or placebo.
• Performance on a validated visual working memory task ('Discrete Whole Report task', 90 trials), alongside assessments of mind wandering and metacognitive accuracy.

Main Results:

• Δ⁹-tetrahydrocannabinol (THC) significantly impaired visual working memory performance (d=0.65).
• THC administration led to increased self-reported mind wandering (Experiment 1).
• THC decreased metacognitive accuracy regarding task performance (Experiment 2).

Conclusions:

• Findings confirm that Δ⁹-tetrahydrocannabinol (THC) impairs visual working memory.
• Impairments may be associated with increased mind wandering and reduced monitoring of cognitive performance.
• Study highlights the critical influence of sample size and task duration on detecting acute drug effects.