A new study shows that casual marijuana use can be linked to changes in brain structures.

According to Fox News researchers at Northwestern University studied the relationship between casual marijuana use and brain changes. They discovered that young people who smoke once or twice a week showed abnormalities in two areas of the brain related to emotion, motivation, and decision-making.

“Just casual use appears to create changes in the brain in areas you don't want to change,” said Hans Breiter, a psychiatrist and mathematician at Northwestern, who was in charge of the study.

Breiter and his team, who collaborated with researchers at Harvard University, studied the brains of 20 college students who use marijuana casually and 20 who don’t use at all, reports USA Today.

They saw volume, shape and density changes in the nucleus accumbens and the amygdala, two areas of the brain involved with motivation and decision-making.

“For the NAC (nucleus accumbens), all three measures were abnormal, and they were abnormal in a dose-dependent way, meaning the changes were greater with the amount of marijuana used,” Breiter said. “The amygdala had abnormalities for shape and density, and only volume correlated with use.

Despite the results, Breiter did state that there are still many unanswered questions about the long-term effects of smoking and that this is merely a “beginning pilot study”.

The study’s full findings will be published on Wednesday in the Journal of Neuroscience.