Elsevier

Biological Psychiatry

Volume 84, Issue 10, 15 November 2018, Pages 743-750
Biological Psychiatry

Archival Report
Δ9-Tetrahydrocannabinol at Retrieval Drives False Recollection of Neutral and Emotional Memories

https://doi.org/10.1016/j.biopsych.2018.04.020Get rights and content

Abstract

Background

It is well established that the main psychoactive constituent of cannabis, Δ9-tetrahydrocannabinol (THC), impairs episodic memory encoding and modulates emotional processing, but little is known about the impact of THC during the retrieval of emotional episodic memories. With the rise of cannabis to treat medical conditions, including those characterized by emotional and episodic memory disturbances, there is an urgent need to determine the effects of THC on memory accuracy and distortion. Here, we report the first study investigating the effects of THC during retrieval of neutral and emotional episodic memories.

Methods

Using a double-blind, placebo-controlled, within-subjects design, healthy volunteers (N = 23) viewed negative, neutral, and positive pictures (emotional memory task) and lists of semantically related words (false memory task). Forty-eight hours later, participants ingested a capsule containing either THC (15 mg) or placebo and completed tasks to test their memories for the previously studied pictures and words.

Results

THC during retrieval did not reduce the number of correct responses to studied items. Instead, it robustly increased false recollection on both the emotional memory and false memory tasks. This effect was found for both neutral and emotional items.

Conclusions

These findings show that THC has adverse effects during memory retrieval, distorting both neutral and emotional memories. Coupled with THC’s known effects during encoding, these new retrieval findings are important in light of the spreading acceptance of cannabis.

Section snippets

Participants

Twenty-four healthy young adults (18–29 years of age, 12 men) with some experience using cannabis (4–100 lifetime occasions) were recruited for the study, but 1 male participant was excluded for not following instructions, leaving 23 participants. Screening included a physical examination, an electrocardiogram, and a semistructured interview by a clinical psychologist. Exclusion criteria included any current DSM-IV Axis I disorder, including substance dependence, current use of >5

Cued Recollection

Full cued recollection data can be found in Table 3. Cued recollection hit rates were directly related to valence (hits [F2,44 = 27.371, p < .001, ηp2 = .554], high-confidence hits [F2,44 = 29.709, p < .001, ηp2 = .575]). As expected, negative stimuli were remembered better than neutral and positive stimuli (Figures 1A and 2A). Relative to placebo, THC did not affect hits (F1,22 = 2.025, p = .169) or high-confidence hits (F1,22 = 0.062, p > .250), nor did it modulate the effect of valence (hits

Discussion

This experiment is the first to find that selectively administering THC during episodic memory retrieval increases false recollection. Evidence for this effect was found across all emotional valences in the emotional memory task and also for neutral words in the DRM task. These findings are consistent with studies using emotionally neutral verbal stimuli showing that THC increases false recognition 2, 34 and recall intrusions 3, 35. However, in those studies participants were intoxicated during

Acknowledgments and Disclosures

This project was supported by Grant No. DA02812 (to HdW).

We thank lab personnel who recruited and screened participants and Royce Lee, M.D., for medical oversight.

HdW has received a GRAND research award from Pfizer, donation of a study drug from Indivior, support for a research study from Insys Therapeutics, and consulting fees from Bristol-Myers-Squibb, Jazz Pharmaceuticals, Marinus, and Organon. None of these were related to the research presented here. The other authors report no biomedical

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