Questioning a study on pot and brain changes


On Wednesday a neuroscience study came out that indicates smoking marijuana changes the size and shape of the brain’s nucleus accumbens, the reward processing center, and the amygdala, which processes emotion.

The study found that in a small subject group, both areas were differently shaped and larger in the pot smokers.

That’s a very interesting finding, certainly.

What strikes me, though, about the study and its authors is that they are announcing the changes are bad without doing any follow up studies on how or if those enlarged regions affect behavior.

Hans Breiter, one of the study’s authors, said in the official release: “This study raises a strong challenge to the idea that casual marijuana use isn’t associated with bad consequences,” Breiter said

Announcing that the results are negative without actually studying the topic first is quintessentially bad and biased science, and it makes the real results of the study seem suspect.

I’m not saying that these enlarged regions would be good or bad.

Generally, though, brain damage coincides with reduced brain areas and activity, not larger ones. If something enlarged the brain’s area used in problem solving, would the authors also consider that bad?

I’m not saying they would or wouldn’t, but it begs the question.

I have a science degree from the University of New Mexico in Earth and Planetary Sciences, and I’m not sure my professors would have let me get away with that sort of pre-judgement.

I’ve added the release to this post. I’d love to hear your thoughts on the topic.


Sue Vorenberg
The Columbian

4/15/2014 | For immediate release


Preliminary study suggests effects of drug even in those who are not addicted

Washington, DC — The size and shape of two brain regions involved in emotion and motivation may differ in young adults who smoke marijuana at least once a week, according to a study published April 16 in The Journal of Neuroscience. The findings suggest that recreational marijuana use may lead to previously unidentified brain changes, and highlight the importance of research aimed at understanding the long-term effects of low to moderate marijuana use on the brain.

Marijuana is the most commonly used illicit drug in the United States, with an estimated 18.9 million people reporting recent use, according to the most current analysis of the National Survey on Drug Use and Mental Health. Marijuana use is often associated with motivation, attention, learning, and memory impairments. Previous studies exposing animals to tetrahydrocannabinol (THC) — the main psychoactive component of marijuana — show that repeated exposure to the drug causes structural changes in brain regions involved with these functions. However, less is known about how low to moderate marijuana use affects brain structure in people, particularly in teens and young adults.

In the current study, Jodi Gilman, PhD, Anne Blood, PhD, and Hans Breiter, MD, of Northwestern University and Massachusetts General Hospital/Harvard Medical School used magnetic resonance imaging (MRI) to compare the brains of 18- to 25-year olds who reported smoking marijuana at least once per week with those with little to no history of marijuana use. Although psychiatric evaluations ruled out the possibility that the marijuana users were dependent on the drug, imaging data revealed they had significant brain differences. The nucleus accumbens — a brain region known to be involved in reward processing — was larger and altered in its shape and structure in the marijuana users compared to non-users.

“This study suggests that even light to moderate recreational marijuana use can cause changes in brain anatomy,” said Carl Lupica, PhD, who studies drug addiction at the National Institute on Drug Abuse, and was not involved with this study. “These observations are particularly interesting because previous studies have focused primarily on the brains of heavy marijuana smokers, and have largely ignored the brains of casual users.”

The team of scientists compared the size, shape, and density of the nucleus accumbens and the amygdala — a brain region that plays a central role in emotion — in 20 marijuana users and 20 non-users. Each marijuana user was asked to estimate their drug consumption over a three-month period, including the number of days they smoked and the amount of the drug consumed each day. The scientists found that the more the marijuana users reported consuming, the greater the abnormalities in the nucleus accumbens and amygdala. The shape and density of both of these regions also differed between marijuana users and non-users.

“This study raises a strong challenge to the idea that casual marijuana use isn’t associated with bad consequences,” Breiter said.

This research was funded by the National Institute on Drug Abuse, the Office of National Drug Control Policy, Counterdrug Technology Assessment Center, and the National Institute of Neurological Disorders and Stroke.

The Journal of Neuroscience is published by the Society for Neuroscience, an organization of nearly 40,000 basic scientists and clinicians who study the brain and nervous system. Gilman can be reached at jgilman1@partners.org, Blood at ablood@nmr.mgh.harvard.edu, and Breiter at h-breiter@northwestern.edu. More information on marijuana and addiction can be found on BrainFacts.org.