A new study from Canada confirms that if certain areas of a person’s brain are abnormally small, that person is more likely to use marijuana. The study also suggests that using the drug probably damages other areas of the brain.
Previous studies have linked long-term abuse of marijuana to certain brain abnormalities, but no one knew if these abnormalities were the result of using the drug, if they existed before marijuana use or if people with such brain abnormalities were simply more likely to use marijuana.
Testing before and after marijuana use
For the new study, Professor Dan Lubman of the Turning Point Alcohol and Drug Center in Monash University worked with researchers from Melbourne University. The team recruited 155 non-drug using 12-year-old children and then performed scans of their brains using magnetic imaging resonance (MRI) technology. Four years later, the team took another set of brain scans. By this time, 28 of the participants were using marijuana.
Dr. Lubman said he chose preteens because “this is an important developmental period to examine. Although not all individuals who initiate cannabis use during this time will go on to use heavily, early cannabis use has been associated with a range of negative outcomes later in life.”
Brain differences are a predictor
The group that was using marijuana had smaller orbitofrontal cortex (OFC) volumes when they were 12 years old. Small OFCs could therefore become a predictor of marijuana use, according to Dr. Lubman. Other regions of the participants’ brains were similar to the non-drug users at the beginning of the study. Since adult marijuana users show lower volumes in other areas of their brains, Dr. Lubman believes that marijuana use causes brain damage.
“What we found is that only the OFC predicted later cannabis use, suggesting that this particular part of the frontal lobe increases an adolescent’s vulnerability to cannabis use,” Dr. Lubman reported. “However, we also found no differences in brain volume in other parts of the brain that we have shown to be abnormal in long-term heavy cannabis users, confirming for the first time, that cannabis use is neurotoxic to these brain areas in humans.”
The OFC is the region of the brain that primarily controls inhibitions and reward-based decision-making. Previous studies of teenage marijuana users had shown that they do not perform as well on tests of problem solving, attention, memory, and executive function as non-drug users.
“These results have important implications for understanding neurobiological predictors of cannabis use, but further research is needed to understand their relationships with heavier patterns of use in adulthood, as well as later abuse of other substances,” according to Dr. Lubman’s report published in the Society of Biological Psychiatry.