Young Adult Cannabis Users Show Thinner Cortex and Smaller Thalamus
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.
Quick Facts
What This Study 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.
Key Numbers
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 They Did This
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.
Why This Research 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 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.
What This Study Doesn't 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.
Questions This Raises
- ?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?
Trust & Context
- Key Stat:
- Smaller thalamus volume correlated with greater impulsivity in cannabis users
- Evidence Grade:
- Small cross-sectional neuroimaging study with well-matched groups but unable to establish causation or directionality.
- Study Age:
- Published in 2015. Neuroimaging techniques and cannabis potency have both evolved.
- Original Title:
- Cortical thinness and volume differences associated with marijuana abuse in emerging adults.
- Published In:
- Drug and alcohol dependence, 155, 275-83 (2015)
- Authors:
- Mashhoon, Y, Sava, S, Sneider, J T, Nickerson, L D, Silveri, M M
- Database ID:
- RTHC-01011
Evidence Hierarchy
A snapshot of a population at one point in time.
What do these levels mean? →Frequently Asked Questions
Does cannabis shrink the brain?
This study found specific structural differences (thinner fusiform gyrus, smaller thalamus) in cannabis users, but could not determine whether cannabis caused these changes or whether pre-existing brain differences made people more likely to use cannabis.
What does the thalamus do?
The thalamus acts as a relay station, routing sensory information and cognitive signals to appropriate brain regions. It plays roles in attention, consciousness, and sensory processing. Smaller thalamic volume was associated with greater impulsivity in this study.
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Cite This Study
https://rethinkthc.com/research/RTHC-01011APA
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
MLA
Mashhoon, Y, et al. "Cortical thinness and volume differences associated with marijuana abuse in emerging adults.." Drug and alcohol dependence, 2015. https://doi.org/10.1016/j.drugalcdep.2015.06.016
RethinkTHC
RethinkTHC Research Database. "Cortical thinness and volume differences associated with mar..." RTHC-01011. Retrieved from https://rethinkthc.com/research/mashhoon-2015-cortical-thinness-and-volume
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.