Emerging adults who used cannabis had thinner cortex in the right fusiform gyrus and significantly smaller thalamic volumes, with smaller thalamus size linked to greater impulsivity.
Read this if you are a young adult cannabis user curious about potential brain structure effects.
Smaller thalamus volume correlated with greater impulsivity in cannabis users
What the researchers found
Researchers compared brain structure in 15 cannabis users and 15 non-users (average age ~22) using high-resolution MRI. The groups were matched on age, education, and alcohol use.
Whole-brain analysis found cannabis users had significantly thinner cortex in the right fusiform gyrus, a region involved in visual processing and face recognition. The expected differences in prefrontal and limbic regions were not found.
More notably, cannabis users had significantly smaller thalamic volume bilaterally. Smaller thalamus size correlated with greater non-planning impulsivity and overall impulsivity scores, suggesting a link between cannabis-associated structural changes and impulsive behavior.
Why it matters
The thalamus acts as a relay station for sensory and cognitive information. Finding that cannabis use is associated with smaller thalamic volume and greater impulsivity suggests a potential mechanism linking cannabis to cognitive and behavioral changes in young adults.
The numbers in context
15 users vs. 15 non-users; right thalamus p=0.05, left thalamus p=0.01; smaller thalamus associated with non-planning impulsivity (p<0.01) and overall impulsivity (p=0.04); right fusiform gyrus significantly thinner (p<0.05)
How the study worked
Cross-sectional study comparing 15 marijuana users and 15 matched non-users. High-resolution structural MRI at 3 Tesla. Cortical thickness and volumetric analyses performed using FreeSurfer. A priori regions of interest included orbitofrontal cortex, cingulate cortex, amygdala, hippocampus, and thalamus.
What this study cannot tell us
Very small sample (15 per group). Cross-sectional design cannot determine whether brain differences preceded or resulted from cannabis use. Predominantly male sample (only 2 females per group). Could not fully control for all potential confounders.
How to read the evidence
Small cross-sectional neuroimaging study with well-matched groups but unable to establish causation or directionality.
When this study was published
Published in 2015. Neuroimaging techniques and cannabis potency have both evolved.
The bigger picture
The thalamus is increasingly recognized as important in addiction neuroscience. Cannabis-associated changes in this region during emerging adulthood, when the brain is still maturing, could have lasting effects on information processing and decision-making.
Questions still open
- Do thalamic volume differences precede cannabis use or result from it? Would these structural changes reverse with abstinence? Is the fusiform gyrus finding related to the subjective visual experiences reported by cannabis users?
Common questions
Does cannabis shrink the brain?
What does the thalamus do?
Read the original research
Cortical thinness and volume differences associated with marijuana abuse in emerging adults.
Drug and alcohol dependence, 155, 275-83
Citation
Mashhoon, Y; Sava, S; Sneider, J T; Nickerson, L D; Silveri, M M. (2015). Cortical thinness and volume differences associated with marijuana abuse in emerging adults.. Drug and alcohol dependence, 155, 275-83. https://doi.org/10.1016/j.drugalcdep.2015.06.016
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)