In healthy cannabis users, THC reduced connectivity between the prefrontal cortex and striatum while CBD enhanced it, with opposite patterns also seen in hippocampal-prefrontal connections.
Read this if you're interested in how THC and CBD affect the brain differently.
THC and CBD had opposite effects on fronto-striatal connectivity
What the researchers found
Researchers administered THC, CBD, or placebo to healthy occasional cannabis users and scanned their brains during a task involving processing novel and salient stimuli. THC and CBD produced opposite effects on functional connectivity between brain regions central to attention and salience processing.
THC reduced connectivity between the dorsal striatum and prefrontal cortex, and this reduction was related to poorer task performance. CBD enhanced this same connection. Conversely, THC increased connectivity between the hippocampus and prefrontal cortex, while CBD reduced it.
These opposite effects on brain network communication occurred in regions involved in determining what is relevant and worth attending to, a process called salience attribution. Disrupted salience processing is a leading theory for how psychotic symptoms arise.
Why it matters
The finding that THC and CBD have opposite effects on brain connectivity in salience-processing regions provides a neural basis for why THC can induce psychotic-like experiences while CBD may protect against them. This has implications for understanding how different cannabis strains or ratios affect the brain.
The numbers in context
Three conditions compared: THC, CBD, placebo. Three key brain regions analyzed: dorsal striatum, prefrontal cortex, hippocampus. THC and CBD showed opposite effects on fronto-striatal and mediotemporal-prefrontal connectivity.
How the study worked
Randomized, placebo-controlled study in healthy occasional cannabis users. Participants received oral THC, CBD, or placebo and underwent fMRI during an oddball salience processing task. Seed cluster-based functional connectivity analysis examined correlations between salience-processing brain regions.
What this study cannot tell us
The sample included only occasional cannabis users, so results may differ in regular or heavy users. Single-dose design does not capture effects of chronic use. The study used oral administration, which differs from smoked or vaped cannabis in onset and metabolism.
How to read the evidence
Randomized, placebo-controlled fMRI study in healthy volunteers. Well-designed but single-dose, single-session protocol.
When this study was published
Published in 2015. THC-CBD interaction research has expanded significantly since.
The bigger picture
The psychosis theory of aberrant salience attribution proposes that psychotic symptoms arise when the brain incorrectly tags irrelevant stimuli as important. THC's disruption and CBD's enhancement of the brain connections involved in this process help explain the contrasting psychiatric profiles of these two cannabinoids.
Questions still open
- Would cannabis strains with higher CBD-to-THC ratios show less disruption of salience network connectivity? Could CBD be used as an adjunct treatment for psychosis by restoring salience processing? Do these connectivity changes persist after chronic use?
Common questions
Do THC and CBD affect the brain differently?
What is salience processing?
Read the original research
Cannabinoid modulation of functional connectivity within regions processing attentional salience.
Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 40(6), 1343-52
Citation
Bhattacharyya, Sagnik; Falkenberg, Irina; Martin-Santos, Rocio; Atakan, Zerrin; Crippa, Jose A; Giampietro, Vincent; Brammer, Mick; McGuire, Philip. (2015). Cannabinoid modulation of functional connectivity within regions processing attentional salience.. Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 40(6), 1343-52. https://doi.org/10.1038/npp.2014.258
Explore the wider topic
- How THC Affects Your Amygdala: The Brain's Threat Detector and Cannabis
- The Anandamide Connection: Your Body's Natural Bliss Molecule
- How Long for Cannabinoid Receptors to Return to Normal
- Cannabis and the Developing Brain: What Every Teenager (and Parent) Should Know
- Why Can't I Enjoy Anything Without Weed? The Science Behind It
- Dopamine Recovery After Quitting Weed: What the Science Says
- The Endocannabinoid System Explained Simply: What It Does and Why It Matters
- Your Endocannabinoid System Explained: Why Withdrawal Happens
- Your Nervous System After Quitting Weed: Fight or Flight
- Using Weed Under 18: What It Does to Your Developing Brain
- What THC Does to Your Brain: Why Withdrawal Happens
- THC and Your Prefrontal Cortex: What Cannabis Does to Your Decision-Making Brain
- Weed, Cortisol, and Stress: What Cannabis Does to Your Stress Hormones
- Weed and Memory: What the Science Says About THC and Your Hippocampus
- Weed and Motivation: Is Amotivational Syndrome Real?
- Weed and Your Nervous System: What THC Actually Does to Your Brain and Body
- How Weed Rewires Your Reward System (And How to Reset It)