Experimental mice have been telling us this for years, but pot-smoking humans didn’t want to believe it could happen to them: 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.
More ambiguously, in regular pot smokers, that region is better connected than it is in nonusers: 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 underperforming gray matter. Whether these “complex neuroadaptive processes” reverse themselves when marijuana use stops is an important unanswered question, they added.
The new findings, reported in the journal PNAS, confirm findings about chronic marijuana use from rodents. But scientific evidence in humans has been more mixed.