Regular Marijuana Users Have Shrunken Brains, Study Finds


Compared with a person who never smoked marijuana, someone who uses marijuana regularly has, on average, less gray matter in his orbital frontal cortex, a region that is a key node in the brain’s reward, motivation, decision-making and addictive behaviors network, says a new study reported by the Los Angeles Times. More ambiguously, in regular pot smokers, that region is better connected than it is in non-users: the flow of signal traffic is speedier to other parts of that motivation and decision-making network, including across the superhighway of “white matter” that connects the brain’s hemispheres.

The researchers who conducted the study speculate that the orbital frontal cortex’s greater level of “connectedness”–which is especially pronounced in people who started smoking pot early in life–may be the brain’s way of compensating for the region’s under-performing gray matter. Whether these “complex neuroadaptive processes” reverse themselves when marijuana use stops is an important unanswered question, they added. The new findings, reported yesterday in the journal PNAS, confirm findings about chronic marijuana use from rodents. But scientific evidence in humans has been more mixed. Even now, the authors of the study acknowledge that they cannot discern whether a pot smoker’s smaller orbital frontal cortex is the cause or the result of chronic marijuana use.

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