THC and CBD had opposite effects on brain areas that process sound and vision | Research

The takeaway

In 14 healthy volunteers, THC decreased brain activation during auditory processing while CBD increased it, with opposite effects in a region linked to language comprehension and psychotic symptoms.

Read this if you want to understand the brain mechanisms behind how THC and CBD differently affect perception.

THC and CBD had opposite effects in the brain's language comprehension area

What the researchers found

Fourteen healthy volunteers were scanned with fMRI on three occasions after receiving THC (10 mg), CBD (600 mg), or placebo. During auditory processing, THC decreased activation in bilateral temporal cortices, while CBD increased activation in the right temporal cortex.

The most striking finding was in the right posterior superior temporal gyrus, the right-hemisphere counterpart to Wernicke's area (critical for language comprehension). THC and CBD had directly opposite effects in this region. THC's attenuation of activation here correlated with its tendency to induce psychotic symptoms.

During visual processing, THC both increased and decreased activation in different visual areas. CBD produced anxiety or psychotic symptom increases in no participants, while THC increased anxiety, intoxication, and positive psychotic symptoms.

Why it matters

The finding that THC-induced changes in a language-related brain area correlated with psychotic symptoms provided a neural mechanism linking cannabis use to psychosis risk. CBD's opposite effect suggested it might counteract this specific vulnerability.

The numbers in context

14 volunteers, 3 sessions each. THC: 10 mg oral. CBD: 600 mg oral. THC and CBD had opposite effects at coordinates 61, -15, -2 (right posterior superior temporal gyrus).

How the study worked

Double-blind, pseudo-randomized crossover design with 14 healthy volunteers. Each participant received 10 mg THC, 600 mg CBD, or placebo on separate occasions. fMRI was recorded during passive listening to words and viewing a radial checkerboard.

What this study cannot tell us

Small sample size (14 volunteers). Single acute doses may not represent chronic use patterns. The tasks were passive (listening, viewing) and may not capture the full range of perceptual effects. CBD dose (600 mg) was much larger than typical consumer doses.

How to read the evidence

Well-designed crossover RCT with neuroimaging, but limited by small sample size. The within-subjects design strengthens internal validity.

When this study was published

Published in 2011. The opposing effects of THC and CBD on brain function have been replicated in subsequent neuroimaging studies.

The bigger picture

Auditory hallucinations are a hallmark of psychosis, and they involve aberrant activation of temporal cortex language areas. THC's disruption of these same areas, correlated with acute psychotic symptoms, provided a potential neurobiological bridge between cannabis use and psychosis.

Questions still open

Could CBD's opposite effect in auditory cortex explain why high-CBD cannabis strains might be less psychotogenic? Do chronic cannabis users show persistent changes in temporal cortex function? Could these findings inform early detection of psychosis vulnerability?

Common questions

Does THC change how the brain processes sound?

Yes. In this study, THC reduced activation in brain areas that process auditory information, particularly in a region important for language comprehension. This disruption correlated with THC-induced psychotic symptoms like altered perception.

Does CBD protect against THC's brain effects?

This study found THC and CBD had directly opposite effects in a key auditory processing region. While this suggests CBD might counteract some of THC's perceptual disruptions, the study tested them separately rather than together.

Read the original research

Modulation of auditory and visual processing by delta-9-tetrahydrocannabinol and cannabidiol: an FMRI study.

Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 36(7), 1340-8

View on PubMed ↗Publisher’s paper ↗

Citation

Winton-Brown, Toby T; Allen, Paul; Bhattacharyya, Sagnik; Borgwardt, Stefan J; Fusar-Poli, Paolo; Crippa, Jose A; Seal, Marc L; Martin-Santos, Rocio; Ffytche, Dominic; Zuardi, Antonio W; Atakan, Zerrin; McGuire, Philip K. (2011). Modulation of auditory and visual processing by delta-9-tetrahydrocannabinol and cannabidiol: an FMRI study.. Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 36(7), 1340-8. https://doi.org/10.1038/npp.2011.17