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Study shows pot has impact on brain

While initial results cannot say whether the enduring effects of cannabis are positive or negative, one thing is certain — habitual use changes the structure of the brain.

Distinguished professor Vince Calhoun, executive science officer at The Mind Research Network, said most of what he does is focused on developing ways to process complex brain imaging data.

The main goal of this study is to evaluate brain volume, functional connectivity and the wiring of the brain, as a measure of overall function in the brains of people who habitually smoke marijuana versus people who don’t, he said.

“We focused on the orbital frontal cortex, which is a frontal portion of the brain that is focused on decision making, inhibition and things like that,” Calhoun said. “One of the things we found is that the grey matter volume was decreased in the cannabis users compared to the healthy controls.”

Grey matter is a region in the brain where the neuron bodies are held. It is essentially where the processing of information occurs and is very important, he said.

Eswar Damaraju, a doctoral candidate in electrical engineering who was involved in the study, said in addition to decreased grey matter volume, they also found initial increases in the corresponding white matter tracts in cannabis users.

White matter refers to regions of the brain that serves as connections between the hemispheres that allows them to communicate. While the study revealed initial increases in white matter, meaning increased connectivity, the effects dropped off over time, he said.

“We used data that we collected from the MRI machine which allowed us to look at how the differ ent regions of the brain communicate with each other,” Damaraju said. “Depending on the duration of marijuana use, we were able to determine the amount of change in the structure of the brain.”

Calhoun said increased connectivity could be positive or negative. One interpretation of the results is that the increased connectivity in cannabis users may have resulted from a compensatory action by the brain to make up for the loss of grey matter volume, he said.

“We thought that perhaps the grey matter regions are working harder to maintain a similar level of function given a decrease in volume,” Calhoun said. “That’s just one interpretation, but what it looks like is that marijuana changes your brain along multiple dimensions.”

More than 100 habitual users of marijuana were matched with healthy non-users based on age, gender and duration of use. All subjects were scanned using the same variety of fMRI techniques in a cross sectional effort to analyze the effects of cannabis on the brain, he said.

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“These folks were chronic marijuana users, so about three times a day typically,” Calhoun said. “We found these effects got bigger the longer they’d smoked and there was a point where it looks like if you smoke it long enough the higher connectivity levels start to drop off, so you lose that compensatory connectivity.”

Calhoun said this is one of the largest studies ever conducted into the effects of habitual cannabis use. Additional research is still needed to reach a definitive conclusion as to whether smoking marijuana has positive of negative effect on the brain.

However, the initial results suggest habitual use of marijuana changes the structure of the brain and therefore should be researched further, he said.

Tomas Lujan is a staff reporter for the Daily Lobo. He can be contacted at or on Twitter @TomasVLujan.

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