Authors of the latest research on cannabis and the brain initially predicted that long-term cannabis consumption would shrink certain brain regions of the participants in the study. Quite to the contrary, they found grey matter volumes did not shrink after four years of “heavy” cannabis consumption, and one region shrank less over time in pot smokers than in the cannabis naive.
Researchers in the Netherlands looked at the conflicting findings between scientists that say pot smokers have smaller brains, bigger brains, and everything in between. Some of these cross-sectional studies analyze brain volumes in a sample of smokers, and compare them to non-tokers. Cross-sectional studies only represent a moment in time and they cannot prove causality in most cases. To be able to say make a real call on the matter, Dutch scientists decided to do a longitudinal experiment to study how cannabis consumption affects the brain over a period of time.
Throughout the experiment, researchers regularly performed MRI’s on 33 weed smokers and 43 “healthy controls.” Starting at an average age of about 20, the participants stayed with study until an average age of 24. Many dropped out of the experiment or were excluded from the dataset, but the sample remained large enough to draw significant conclusions.
With their results they could conclude that smoking cannabis “during late adolescence and early adulthood does not change GM [grey matter] morphology.” Dutch researchers did not observe a reduction in grey matter volumes, but the cross-section still showed cannabis consumers had less grey matter in their medial-temporal lobes. It seems many of the smokers simply started out with slightly smaller medial-temporal lobe, but they don’t know if cannabis caused the reduced volume, or whether reduced volume makes a person more likely to consume cannabis.
Surprisingly, their research found that pot smokers had larger cerebelli. The cerebellum (a region at the back of the brain that contributes to motor control, coordination, language, etc.) naturally shrinks as we get older, it seems cannabis may somehow prevent shrinkage.
The main limitation of this study was that the researchers could not observe the adolescents’ brains as they started to smoke weed; they caught them after they were already habitual smokers. This could lead them to think that smoking cannabis at an early age caused certain regions of the brain to shrink during development, but what if their brains’ happen to start out that way?
A study published in October of 2015 used data from the Human Connectome Project (a massive, multinational research effort to unravel the links between all the neurons in the brain) to show that cannabis isn’t the cause for the brain abnormalities, genetics are. They looked at MRI’s from pairs of twins in which one twin smoked weed, and the other did not. They found that even though a pot-smoking twin may have had a smaller medial-temporal lobe, the other, straightedge twin did also.
Despite this research, other studies show that smoking cannabis during early adolescence can have a negative impact on the white matter in the brain. However, the “age of initiation” had a huge effect on the severity of the disturbances. Though chronic cannabis consumption may not have a significant negative impact on cognition in grown adults, young adolescents shouldn’t smoke so as to not harm their developing brains. Cannabis isn’t alone on this list; nicotine, alcohol, caffeine and many prescription drugs can also cause harm to minds and bodies of children and adolescents.
Photo Credit: Vortex Farmacy
