A new study out of the University of Texas' Center for BrainHealth and the Mind Research Network is showing brain differences in regular pot users—differences that have already been reported in lab mice. The study, published in PNAS, found that 48 "chronic" users who smoked at least four times a week had less gray matter in the orbitofrontal cortex than 62 control subjects who didn't use pot, reports the Los Angeles Times. The orbitofrontal cortex "helps us determine what is good for us and what keeps us sustained," the lead author tells the Washington Post. It's unclear whether these "shrunken brains" are the result of chronic use or contribute to the tendency to use in the first place.
Researchers also found that the orbitofrontal cortex is better connected in chronic users, with a faster signal flow throughout the motivation- and decision-making network and even across the white matter connecting the brain's left and right hemispheres. One possible explanation? That increased "connectedness" might be compensating for the not-up-to-snuff gray matter. That finding was more pronounced for users who started smoking pot young, "which may explain why chronic, long-term users 'seem to be doing just fine' despite smaller OFC brain volumes," according to a release. An earlier study from 2012 found that 12-year-olds with smaller orbitofrontal cortices were more likely to start using pot by age 16, indicating a possible predisposition to marijuana use in those with deficits in this part of the brain. (Marijuana use has also been linked to heart problems.)