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According to a new paper published in The Journal of Neuroscience, young adults who casually smoke weed sustain changes to areas of the brain associated with emotion and (you guessed it) motivation. 

The study, by scientists from Northwestern Medicine and Massachusetts General Hospital and Harvard Medical School, is novel because it looks at young smokers who don't use the drug heavily, a population largely ignored by comparable studies. According to the researchers, there's a pretty direct joint-to-brain-change ratio among participants. The Boston Globe offers some detail on the methodology: 

Forty Boston-area young adults aged 18 to 25, many from Boston University, were selected for the study. Researchers used scans to measure the volume, shape, and density of two regions of the brain — the nucleus accumbens and the amygdala. Half of the group said they used marijuana at least once a week, and the other 20 had not used the drug in the past year, and reported using it less than five times in their life. Among the group that did smoke, the median use was about six joints per week. Scans revealed that the nucleus accumbens was larger in marijuana users, compared with nonusers, and its alteration was directly related to how much the person smoked. 

But the study doesn't offer much beyond the fact that, among the rather small sample size, brain changes correlate to marijuana use. The research doesn't focus on whether the alterations are related to a decline in brain function, or if they are permanent. Still, according to lead author Jodi Gilman, brain changes among teen and young-adult users are significant because “This is when you are making major decisions in your life, when you are choosing a major, starting a career, making long-lasting friendships and relationships." 

The findings come at a time when most Americans support legalizing marijuana, and a number of states are following in Colorado's lucrative footsteps by planning to make commercial weed sales legit. But it also follows the first death officially linked to pot use in Colorado, and the authors say that the study suggests that "further study of marijuana effects are needed to help inform discussion about the legalization of marijuana." We'll see about that. 

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