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Over the years there has been a running debate among users and non-users of marijuana as to the effects the drug has on the brain. Non-users say it reacts in the body much the same as alcohol abuse, with slower memory and reflexes. Users say there is no change in the brain chemistry or function, and it is safe to use. Up until now there have been no definitive studies to prove or disprove anything.

Australian researchers from Melbourne University, along with Professor Dan Lubman from Turning Point Alcohol and Drug Centre and Monash University set out to find whether heavy marijuana (cannabis) usage would have an effect on the brain and its functions, and if there is a possibility that there are abnormalities existing in the brain prior to usage that are markers for cannabis use later on. Their study was published online in Biological Psychiatry, the official journal of the Society of Biological Psychiatry.

Researchers were able to prove that cannabis use does indeed harm the brain, but there may have been irregularities in the brain before the usage started in the frontal lobe area. “Previous evidence has shown that long-term heavy cannabis use is associated with alterations in regional brain volumes,” Professor Lubman said. “Although these changes are frequently attributed to the neurotoxic effects of cannabis, no studies have examined whether structural brain abnormalities are present before the onset of cannabis use until now.”

To answer their study, students from primary schools in Melbourne were recruited as part of a larger study on emotional development in adolescents. Four years after initial magnetic resonance imaging (MRI) tests were run on 155 12-year-old participants, 121 adolescents did a follow-up survey and measurements. Out of the remaining group that was then 16, 28 had started marijuana use.

“This is an important developmental period to examine, because 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,” Professor Lubman said.

What they found was that those who had smaller volumes of the frontal lobes of the brain, the orbitofrontal cortex (OFC) at age 12 were more likely to have initiated cannabis use by age 16. Volumes of other regions of the brain did not seem to be predicators of later marijuana use. “Given the lack of research in this area, we hypothesized that pre-drug use differences would be consistent with the structural abnormalities that have been found in studies of heavy users,” Professor Lubman said.

“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. However, we also found no differences in brain volume in other parts of the brain that we have found 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 plays a key role in reward-based decision-making and control of emotions. Previous studies of adolescent marijuana users have shown subtle damage in problem-solving, attention, memory and executive functions. “In adult cannabis users, decreased activation of the OFC has been associated with faulty decision-making, suggesting that a reduced ability to weigh the pros and costs of one’s actions might render certain individuals more prone to drug problems,” Professor Lubman said.

“These results have important implications for understanding neurobiological predictors of cannabis use, but further research is still needed to understand their relationships with heavier patterns of use in adulthood as well as later abuse of other substances,” Lubman stated. 

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About the author:

Ron White is a two-time USA Memory Champion . He speaks at seminars and to large groups all over the world on how to improve memory and memory techniques.

 

Sources:

Medical Xpress – Cannabis harms the brain – but that’s not the full story: http://medicalxpress.com/news/2011-12-cannabis-brain-full-story.html