According to a study released on Wednesday, April 16, in the Journal of Neuroscience, the shape and size of two regions in the brain differ in marijuana smokers (young adults) who smoke at least once a week. These parts, the amygdala and the nucleus accumbens, are particularly involved in motivation and emotion. Although only a small study, the findings suggest that even recreational use of the plant may lead some changes in the brain, and that further research about the long-term brain effects of moderate use of marijuana is needed.

This is not the first time that recreational marijuana smoking has been connected to significant differences in the brain, and the findings are consistent with previous experiments on rats, but other studies of humans have found no significant differences. This study did not show whether or not the changes were caused by the marijuana usage or were preexisting differences that predisposed participants to marijuana use had, nor did it address how long-lasting the differences were. The study was a collaboration led by Jodi Gilman, a psychology instructor at Harvard Medical School and a brain scientist at Massachusetts General Hospital. The subjects were 20 marijuana-smokers and 20 non-marijuana-smokers, aged 18 to 25.

Based on the imaging data, the two groups of respondents have significant brain differences. The part of the brain known as the nucleus accumbens was seen to be bigger and different in shape and structure among the users compared to non-users. This is the region of the brain associated with motivation or reward processing. The team also compared their amygdala, which is associated with emotion, taking note of differences in shape, size and nucleus density.

The pot users were instructed to note their consumption of marijuana in the last three months, which includes the amount of substance consumed each day. The researchers found that the more they use it, the more pronounced abnormalities are in the specified regions of the brain. This raises questions about the notion that casual marijuana use has no negative consequences, a question of increasing importance while several entities are affirming that marijuana can be beneficial to health, proposing that medical or recreational marijuana be legalized in many places.