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Heavy Marijuana Use Shrinks Brain, But Compensates With More Connections: Study

11/11/2014 12:43 EST | Updated 11/11/2014 12:59 EST

Don't be alarmed, but smoking a lot of pot for a long time may shrink your brain.

At least, that's the conclusion U.S. neuroscientists have reached from the first long-term probe into the brains of heavy marijuana smokers.

But they also suggest a silver lining: The heavy pot smoker's brain may be a whiz at making connections.

In the study, conducted at the Centre for Brain Health at the University of Texas, researchers noted key differences between the brains of long-term pot smokers and their non-smoking peers.

“We have seen a steady increase in the incidence of marijuana use since 2007," Dr. Francesca Filbey, lead author of the study noted. “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.”

Specifically, they looked at the orbitofrontal cortex, or OFC, a murky region of the brain often associated with decision-making.

Or, as scientists Carmen Cavada and Wolfram Schultz pointed out in a 2000 paper, "social adjustment and the control of mood, drive and responsibility, traits that are crucial in defining the ‘personality’ of an individual."

In the University of Texas study, researchers used multiple MRI scans to detect differences in the volume of a pot smoker's OFC, compared to that of a non-smoker.

To put it bluntly, the pot-smoker's cortex did not appear quite so weighty.

If a subject started smoking marijuana at a relatively young age, however, researchers found a compensating trend — the brain showed a knack for connectivity, specifically in how intricately connected the OFC was to other areas of the brain.

“What’s unique about this work is that it combines three different MRI techniques to evaluate different brain characteristics,” Dr. Sina Aslan of the University of Texas explained. “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.”

How long one had been smoking pot for, as well as their age at the time of the study, were key factors in the brain's seemingly heightened connectivity.

For the study, the team looked a relatively big sample size -- 48 adult pot smokers, as well as 62 gender- and age-matched non-smokers.

Result-skewering biases, such as gender, age and ethnicity, were ironed out. And pot users were categorized according to how heavily they indulged.

The study was published this week in the Proceedings of the National Academy of Sciences. You can read it here.

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