Marijuana Use On A Casual Basis Still Linked To Brain Abnormalities
April 16, 2014

Casual Pot Use Linked To Brain Deformation

Brett Smith for - Your Universe Online

With the movement to legalize marijuana appearing to gain momentum across the US, new attention is being given to the negative effects the drug has on the brain.

According to a new study published on Wednesday in the Journal of Neuroscience, even causal use of marijuana can have a significant impact of the shape, volume and density of certain brain regions. The study team also found that the more marijuana a person smoked – the more abnormal their brain becomes.

"This study raises a strong challenge to the idea that casual marijuana use isn't associated with bad consequences," said study author Dr. Hans Breiter, a professor of psychiatry and behavioral sciences at Northwestern University.

"Some of these people only used marijuana to get high once or twice a week," Breiter added. "People think a little recreational use shouldn't cause a problem, if someone is doing OK with work or school. Our data directly says this is not the case."

In the study, researchers used neuroimaging to analyze the brains of two groups of 18- to 25-year-olds: 20 casual marijuana smokers and 20 participants who did not smoke marijuana. Each group included 9 males and 11 females. The researchers used interviews to confirm users were not reliant on marijuana and were not users of any other illegal drugs.

Breiter said the team used three measures to create a multidimensional integrated view of participants’ brains: shape, volume and density. Scientists focused particularly on the nucleus accumbens and the amygdala – crucial regions for feelings and motivation that are also affiliated with addiction.

"These are core, fundamental structures of the brain," said study author Anne Blood, assistant professor of psychiatry at Harvard Medical School. "They form the basis for how you assess positive and negative features about things in the environment and make decisions about them."

The study team found variations in brain components reveal that marijuana users' brains are adjusting to low-level exposure to marijuana. The result is consistent with animal reports that show when rodents are given tetrahydrocannabinol (THC) – the psychoactive ingredient in pot – their brains re-shape and generate several new links.

"It may be that we're seeing a type of drug learning in the brain," said study author Jodi Gilman, an instructor in psychology at Harvard Medical School. "We think when people are in the process of becoming addicted, their brains form these new connections."

In animal models, these new connections formed by marijuana use reveal the brain is adjusting to the unnatural degree of reward and arousal from marijuana. These connections are thought to make other normal rewards less gratifying.

"Drugs of abuse can cause more dopamine release than natural rewards like food, sex and social interaction," Gilman said. "In those you also get a burst of dopamine but not as much as in many drugs of abuse. That is why drugs take on so much salience, and everything else loses its importance."

"Further work, including longitudinal studies, is needed to determine if these findings can be linked to animal studies showing marijuana can be a gateway drug for stronger substances," Breiter said.