Heavy marijuana use dulls the brains of young people, mostly affecting their short-term working memory, according to a new study.
Magnetic resonance imaging scans showed weaker brain activation in marijuana users who performed tasks that tested their ability to temporarily store a limited amount of information in readiness for immediate mental use, according to results published in JAMA Network Open.
"A lifetime history of heavy cannabis use is associated with lower brain activation associated with working memory, with a small to medium effect size," concluded the research team, led by Joshua Gowin, associate professor of radiology at the University of Colorado Anschutz Medical Campus.
Previous research has linked marijuana use to reduced memory, planning, decision-making, and social abilities, but those studies typically contained few participants who were regular or heavy pot users, the team notes.
For the study, the researchers analyzed MRI scans and cognitive tests performed on more than 1,000 young adults as part of a large-scale project to comprehensively map the human brain.
Participants underwent MRI brain scans while performing 7 different tasks related to brain function, researchers say.
They classified about 9% of the participants as heavy pot users, as they indicated in the questionnaire that they had used cannabis 1000 times or more.
Another 18% were considered moderate users because they reported having used pot 10 to 999 times. The remainder were considered non-users.
The results showed lower activation of certain brain regions during the working memory task among heavy pot users, the researchers said.
These regions included the anterior insula, a region associated with emotional processing, and the medial prefrontal cortex and dorsolateral prefrontal cortex, regions associated with higher-level functions such as planning, decision making, cognitive flexibility, and working memory.
"These are regions that have a relatively high density of (cannabinoid) receptors," the researchers write, and may therefore be affected by heavy pot use.
The study also found that recent pot use was associated with poorer performance and less brain activation during working memory tests, but the associations were not statistically significant.
"The association we observed between recent use and activation on working memory and performance tasks suggests that abstaining from cannabis before situations requiring cognitive effort is likely to help performance. The exact duration of this period of abstinence is unclear, but studies suggest that residual cognitive effects of cannabis may persist for 2 to 4 weeks after abstinence," the researchers state.
According to the researchers, larger studies are needed to track the effects of pot use on brain function.
In the meantime, "our findings underscore the need to educate cannabis users about the effects of recent and intensive lifelong cannabis use on cognitively demanding working memory tasks," they conclude. | BGNES
