Regular marijuana users have increased connectivity in their brains, despite having some gray matter loss in areas related to addiction, a study finds.
The research, published in the Proceedings of the National Academy of Sciences, is the first to use multiple brain scanning techniques to examine both the structure and function of the brain.
Dr. Sina Aslan, one of the study’s authors, explained:
“What’s unique about this work is that it combines three different MRI techniques to evaluate different brain characteristics.
The results suggest increases in connectivity, both structural and functional that may be compensating for gray matter losses.
Eventually, however, the structural connectivity or ‘wiring’ of the brain starts degrading with prolonged marijuana use.”
The study involved 48 adult marijuana users who used the drug, on average, three times a day (Filbey et al., 2014).
They were compared to 62 matched non-users of marijuana.
The researchers found that the pattern of changes in both connectivity and structure of the brain depended on when and how often the drug was used.
Increases in connectivity were greatest when people began to use the drug and, the more they used it, the greater those increases.
Over time, though, an area of the brain called the orbitofrontal cortex is smaller in long-term marijuana users.
This area is crucial in how we make decisions and is central to how to brain processes rewards.
Taken together, this may explain why long-term marijuana users often seem to be doing reasonably well: structural losses in one area are being compensated for by connectivity gains.
It may also explain why the studies on marijuana’s effects on the brain have been so varied — some saying there is little damage, others more alarmist.
Dr. Francesca Filbey, who led the study, said:
“To date, existing studies on the long-term effects of marijuana on brain structures have been largely inconclusive due to limitations in methodologies.
While our study does not conclusively address whether any or all of the brain changes are a direct consequence of marijuana use, these effects do suggest that these changes are related to age of onset and duration of use.”
We still don’t know, though, the long-term effects of occasional marijuana use or whether the changes revert back to normal after drug-use is stopped.
Dr. Filbey concluded:
“We have seen a steady increase in the incidence of marijuana use since 2007.
However, research on its long-term effects remains scarce despite the changes in legislation surrounding marijuana and the continuing conversation surrounding this relevant public health topic.”
This study provides a fascinating insight into a controversial area.
About the author
Psychologist, Jeremy Dean, PhD is the founder and author of PsyBlog. He holds a doctorate in psychology from University College London and two other advanced degrees in psychology.
He has been writing about scientific research on PsyBlog since 2004. He is also the author of the book “Making Habits, Breaking Habits” (Da Capo, 2013) and several ebooks:
- Accept Yourself: How to feel a profound sense of warmth and self-compassion
- The Anxiety Plan: 42 Strategies For Worry, Phobias, OCD and Panic
- Spark: 17 Steps That Will Boost Your Motivation For Anything
- Activate: How To Find Joy Again By Changing What You Do
Image credit: ashton