UPDATED: April 18, 2014, at 4:42 p.m.

In a recent study, Jodi Gilman, a professor of psychiatry at Harvard Medical School, discovered brain abnormalities in young adults who are marijuana smokers. According to Gilman’s research, brain regions related to decision-making, motivation, and emotional processing in participants tended to be compromised.

In the study, which was published in the Journal of Neuroscience, findings revealed differences in the mind of young adult marijuana users, at an age when their brains were still developing.

Gilman and co-author Hans Breiter from Massachusetts General Hospital recruited 40 young adults from the Boston area ranging from 18 to 25 years old. Half of the participants smoked marijuana regularly—a minimum of one time per week—while the other half did not smoke at all. After conducting MRIs and comparing the size, shape, and density of different structures in the brain, the researchers found noteworthy differences in the nucleus accumbens and amygdala.

Gilman pointed out, however, that the study did not look for differences in the subjects’ behavior, and that more research should be done before determining the safety of marijuana use.

Nathan Greenslit, who teaches a History of Science course on “The Historical and Cultural Lives of Drugs in the U.S.,” agreed that while the study looked at changes in the brain’s physical structure, it did not necessarily indicate any changes in behavior.

“The study did not make any claims about how marijuana differently affected cognition or behavior in these groups. It literally just tried to establish that the aggregated brain images of the two groups look different,” Greenslit said.

Although it is commonly accepted that drugs affect the brain, this study is unique in that the participants were occasional users rather than long-term heavy users, Gilman said. Participant criteria dictated that they had to be “casual” users, who smoked at least once a week and showed no dependency or addiction on marijuana.

“The study in question basically invents two new categories of person: the young ‘casual’ marijuana user and the young non-marijuana user,” Greenslit said. “It’s an example of turning to brain imaging to make seemingly objective what we only care about in the first place because of a unique political history surrounding the criminalization of a plant."

Gilman said that the importance of the experiment lies in the age group of the participants, since young adults are making big decisions regarding their majors, careers, and relationships at this time of their lives.

"If the participants stopped using marijuana, we don't know if, let's say in a year, the abnormalities would normalize," Gilman said.

Gilman also admitted more research needs to be done in order to see how these brain abnormalities relate to behavior and to make larger claims.

"The marijuana used today is much stronger than what people used to see, and we don't know the effects," Gilman said. "We need to be cautious before we have the data."

This article has been revised to reflect the following correction:

CORRECTION: April 18, 2014

An earlier version of this article incorrectly stated the name of the journal in which Gilman's study was published. In fact, it was published in the Journal of Neuroscience.