Heavy cannabis use among young adults can mess with working memory

A lifetime history of heavy cannabis use among young adults appears to exert a long-lasting detrimental effect on working memory, according to a cross-sectional study.

Researchers used data from the Human Connectome Project and identified 1,003 adults (mean age 28.7 years, 46.9 percent male, 76.0 percent White) for analysis.

History of heavy cannabis use was determined using the Semi-Structured Assessment for the Genetics of Alcoholism, with variables for lifetime history and diagnosis of cannabis dependence. Participants with greater than 1,000 uses were grouped as heavy lifetime cannabis users, those who had 10–999 uses were grouped as moderate users, and those with fewer than 10 uses were grouped as nonusers. Urine samples on the day of scanning were collected and analysed to assess recent use. All participants performed seven tasks during the functional MRI session to assess brain activation.

Of the participants, 88 were heavy lifetime cannabis users (8.8 percent), 179 were moderate users (17.8 percent), and 736 were nonusers (73.4 percent). Linear mixed-effects regression model showed an association between heavy lifetime use and lower activation on the working memory task (Cohen d, −0.28, 95 percent confidence interval, −0.50 to −0.06; p=0.02 for false discovery rate correction). Brain regions associated with a history of heavy use were the anterior insula, medial prefrontal cortex, and dorsolateral prefrontal cortex.

Meanwhile, recent cannabis use was associated with poorer performance and lower brain activation in the working memory and motor tasks. However, the associations with brain activation did not survive false discovery rate correction. No other tasks showed a significant link to lifetime history of heavy use, recent use, or a diagnosis of dependence.