Study Links Casual Pot Use With Brain Abnormalities

Apr 16, 2014
Originally published on April 16, 2014 12:30 pm

Young adults who smoke marijuana at least once a week showed changes in the size and shape of two key brain regions, according to a new study of 20 pot smokers and 20 non-pot smokers between 18 and 25.

This is the first time recreational marijuana use has been connected to significant brain changes.

The findings, a collaboration between Northwestern University and Massachusetts General Hospital/Harvard Medical School, were published in The Journal of Neuroscience.

The senior author of the study, Hans Breiter, joins Here & Now’s Robin Young to discuss the research.

Interview Highlights: Hans Breiter

On the findings of the study

“Basically we looked in at two critical structures for reward processing and judgement decision making and also the processing of emotion. And we found that these two structures were abnormal in these casual users compared to well-matched healthy controls.”

On the reward processing part of the brain

“A fundamental aspect of addiction research has been this concept of reward and that substances of abuse basically kind of hijack this system and substitute for things that are naturally rewarding such as food or playing with your kids or taking a moment to read a piece of Proust or something. Since early work in the ’90s, we found that the nucleus accumbens is basically one of many many regions of the brain that process what is positive and negative for a person and facilitates making judgments and decisions based on these assessments of what’s positive and negative.”

On the small sample size and self-reporting of pot use

“This is an excellent question and it’s a question that gets raised in any type of study where you take a sample of society and then try to extrapolate out from it. We used statistics that allow for random effects analysis. We looked at the data in multiple ways. I myself am known as a bit of a conservative neuro-imager and don’t publish things unless I believe it’s going to be replicated. But it gets to this issue, how can you extrapolate from 40 people to the rest of society — you can’t. This is a pilot study, absolutely needs to be verified with larger cohorts and in cohorts around the country. There’s no way with just 40 people that you can sample the diversity of a country with as much diversity as we have.”

Guest

  • Hans Breiter, professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine and senior author of the study.
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Transcript

JEREMY HOBSON, HOST:

From NPR and WBUR Boston, I'm Jeremy Hobson.

ROBIN YOUNG, HOST:

I'm Robin Young. It's HERE AND NOW. A new study published today concludes that casual use of marijuana, once-a-week use, can lead to previously unidentified changes in the brains of 18 to 25-year-olds.

HOBSON: In a moment, we'll talk about drug treatment for high school students right inside the school building.

YOUNG: But first to that study, a collaboration between Northwestern University Medicine and Massachusetts General Hospital Harvard Medical School. It was published in the Journal of Neuroscience. Hans Breiter is professor of psychiatry and behavioral sciences at Northwestern. He was senior author on the study. So, professor, to your findings, you say the casual use of marijuana changed the brains of young people. How so?

HANS BREITER: Well, basically, we looked in at two critical structures for reward processing and judgment and decision-making, and also the processing of emotion. And we found that these two structures were abnormal in these casual users, compared to well-matched healthy controls.

YOUNG: Well, tell us more about these parts of the brain. We know about decision-making and things like that, but the part of the brain that is involved in reward processing, what does that mean?

BREITER: A fundamental aspect of addiction research has been this concept of reward, and that substances of abuse, basically, they kind of hijack this system and substitute for things that are naturally rewarding, such as food or playing with your kids or taking a moment to read a piece of Proust or something.

Since early work in the '90s, we found that the nucleus accumbens is basically one of many, many regions of the brain that process what is positive and negative for a person and facilitate making judgments and decisions based on these assessments of what's positive and negative.

YOUNG: So, in other words, this does something to the part of the brain that might be triggering the need for more and more use of something like marijuana to feed that part of the brain, the reward part of the brain?

BREITER: Yes. And, in fact, the animal work that's been done shows that the nucleus accumbens does change. Our work, by showing that the volume, the density and the shape of this region of the brain changes and relates in a dose response way to the cannabis, is very much in parallel with what's been seen with animals.

YOUNG: Well, and you used MRIs to compare the brains of these 18 to 25-year-olds who reported smoking marijuana at least once a week with those who had little or absolutely no history of marijuana smoking. But there are questions about the research, because we understand a very small study, only 40 young people, 20 who reported smoking pot casually, 20 who didn't at all. Is that really enough people to come to a conclusion?

And these young people did self-report. I know that there was psychological testing to back up their claims, but how can you be sure?

BREITER: This is an excellent question, and it's a question that gets raised in any type of study where you take a sample of society and then try to extrapolate out from it. We used statistics that allow for random effects analysis. We've looked at the data in multiple ways. I myself am known as being a bit of a conservative neuro-imager, and don't publish things unless I believe it's going to be replicated.

But it gets to this issue: How can you extrapolate from 40 people to the rest of society? You can't. This is a pilot study, absolutely needs to be verified with larger cohorts, and in cohorts across the country. There's no way with just 40 people that you can sample the diversity of a country with as much diversity as we have.

YOUNG: Well, what do you think this does say, though, just on the face of it, to marijuana legalization advocates, who argue that marijuana is safer than alcohol? Now, we know that previous studies, as we said, looked at the brains of heavy marijuana smokers and saw some effect there. But this is casual use. So what do you say to people who say casual use is much safer?

BREITER: I say to them that this is the shot across the bow, that we need to actually study this more. By showing that there's abnormalities in the brains of people who use casually, we've indicated that there's something not right with this piece of folklore.

YOUNG: Hans Breiter, professor in psychiatry and behavioral sciences at Northwestern Medicine. He's also senior author on the study, which appears in today's Journal of Neuroscience, on the effects of casual, very casual marijuana use on the brains of young people, a study in collaboration with Mass General Hospital and Harvard Medical School, and published in the Journal of Neuroscience. Professor, I'm sure you've got some conversations started. Thank you.

BREITER: Thank you. Transcript provided by NPR, Copyright NPR.