Brain imaging found that chronic cannabis users showed altered activation patterns in regions involved in understanding other people's mental states, similar to patterns seen in people at risk for psychosis.
Read this if you are a regular cannabis user and have noticed changes in how you read social situations.
Activation patterns matched those seen in psychosis at-risk populations
What the researchers found
Fifteen chronic cannabis users and 14 controls underwent brain imaging while performing a theory of mind task (interpreting cartoon stories that required understanding characters' intentions). Cannabis users showed less activation in the left parahippocampal gyrus, right precuneus, and right cuneus, but greater activation in the left cuneus and right anterior cingulate gyrus.
These activation patterns resembled those previously documented in populations at risk for developing psychosis, suggesting that cannabis use affects social cognitive processing in ways that parallel other psychosis risk factors.
Why it matters
Theory of mind, the ability to understand what others are thinking and feeling, is a core social cognitive skill that is impaired in schizophrenia. Finding that chronic cannabis users show similar brain activation abnormalities suggests cannabis may affect the neural circuits underlying social cognition.
The numbers in context
15 cannabis users vs. 14 controls. Altered activation found in 5 brain regions: reduced in left parahippocampal gyrus, right precuneus, right cuneus; increased in left cuneus and right anterior cingulate gyrus.
How the study worked
Functional brain imaging (fMRI) during performance of a cartoon story task requiring theory of mind. Fifteen chronic cannabis users were compared to 14 healthy controls. Brain activation patterns were analyzed for between-group differences.
What this study cannot tell us
The sample was small (15 users, 14 controls), limiting statistical power. The cross-sectional design cannot determine whether cannabis use caused the brain changes or whether pre-existing differences led people to use cannabis. Other substances used by participants could have contributed to the findings.
How to read the evidence
Small cross-sectional neuroimaging study; preliminary evidence that cannot establish causation.
When this study was published
Published in 2012. Neuroimaging research on cannabis and social cognition has expanded with larger samples.
The bigger picture
This study adds to the evidence linking chronic cannabis use to psychosis-like brain changes. The social cognition angle is particularly relevant because theory of mind deficits are among the most functionally disabling aspects of psychotic disorders, affecting relationships and daily functioning.
Questions still open
- Do these brain activation changes reverse with cannabis abstinence? Do they predict who will go on to develop psychotic disorders? Are the activation changes associated with actual impairments in real-world social functioning?
Common questions
What is theory of mind?
Does this mean cannabis causes psychosis-like brain changes?
Read the original research
Alterations of theory of mind network activation in chronic cannabis users.
Schizophrenia research, 139(1-3), 19-26
Citation
Roser, Patrik; Lissek, Silke; Tegenthoff, Martin; Nicolas, Volkmar; Juckel, Georg; Brüne, Martin. (2012). Alterations of theory of mind network activation in chronic cannabis users.. Schizophrenia research, 139(1-3), 19-26. https://doi.org/10.1016/j.schres.2012.05.020
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)