Rat study finds high-THC cannabis smoke impairs working memory but not attention, while high-CBD smoke does not | Research

The takeaway

In rats, acute exposure to high-THC cannabis smoke impaired working memory but left attention and impulsivity unaffected, while high-CBD cannabis smoke had no measurable cognitive effects.

Readers interested in how different cannabis strains affect specific types of thinking and memory.

Working memory impaired by THC; attention and impulsivity unaffected

What the researchers found

High-THC cannabis smoke and THC injections impaired working memory on the TUNL task but had no effect on attention, impulsivity, or perseveration on the 5-CSRTT. High-CBD, low-THC smoke produced no cognitive impairments.

Why it matters

This study directly compares different cannabis chemotypes (high-THC vs. high-CBD) on specific cognitive domains, helping clarify which cognitive functions are most vulnerable to THC.

The numbers in context

THC injections produced significantly higher plasma THC than smoke exposure at 30 minutes post-treatment. High-CBD smoke significantly increased plasma CBD levels. Performance was worse at smaller spatial separations across all groups.

How the study worked

Adult male rats were acutely exposed to smoke from high-THC (Mohawk) or low-THC/high-CBD (Treasure Island) cannabis strains via inhalation chamber, or received THC injections (3.0 mg/kg i.p.). Cognitive performance was assessed using touchscreen-based TUNL (working memory) and 5-CSRTT (attention) tasks. Plasma cannabinoid levels were measured.

What this study cannot tell us

Only male rats were tested. Acute exposure only, so chronic effects remain unknown. Smoke inhalation dosing is less precise than injection. The specific cannabis strains used may not represent all products available to humans.

How to read the evidence

Well-controlled animal study with multiple comparisons, but findings may not directly translate to humans.

When this study was published

Published in 2022.

The bigger picture

The finding that working memory is more sensitive to THC than attention or impulsivity suggests these cognitive domains have different thresholds for cannabinoid disruption, which may inform understanding of how different cannabis products affect daily functioning.

Questions still open

Would chronic exposure produce different patterns? Do female rats show the same selective vulnerability of working memory? Could CBD in the high-CBD strain be actively protecting against cognitive impairment?

Common questions

Which cognitive function was most affected by THC?

Working memory, tested using a touchscreen spatial task, was significantly impaired by both THC smoke and injection. Attention and impulsivity were not affected by any treatment.

Did the high-CBD cannabis strain cause any cognitive problems?

No. The low-THC, high-CBD strain (Treasure Island) did not impair working memory, attention, or any other measure, despite significantly increasing CBD levels in blood.

Read the original research

The effects of acute Cannabis smoke or Δ9-THC injections on the trial-unique, nonmatching-to-location and five-choice serial reaction time tasks in male Long-Evans rats.

Neurobiology of learning and memory, 192, 107624

View on PubMed ↗Publisher’s paper ↗

Citation

Barnard, Ilne L; Onofrychuk, Timothy J; Sandini, Thaísa M; McElroy, Dan L; Zagzoog, Ayat; Roebuck, Andrew J; Austin-Scott, Faith V; Laprairie, Robert B; Howland, John G. (2022). The effects of acute Cannabis smoke or Δ9-THC injections on the trial-unique, nonmatching-to-location and five-choice serial reaction time tasks in male Long-Evans rats.. Neurobiology of learning and memory, 192, 107624. https://doi.org/10.1016/j.nlm.2022.107624