Following driving directions or recalling a phone number are skills that require "working memory" – an executive function that helps people keep track of what they are doing.
"Working memory is sort of a category above attention," Matthew Cruger, a clinical neuropsychologist in the Learning and Development Center at the Child Mind Institute in New York, said in an article published by the institute last fall. "It's keeping in mind anything you need to keep in mind while you're doing something."
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People who have recently used cannabis, or who use it heavily, may be damaging their working memory, according to a study published Tuesday in JAMA Open Network. Heavy cannabis use was associated with reduced activity in regions of the brain involved in cognitive functions, such as decision-making, memory, attention and emotional processing. One of the largest studies on the impact of cannabis on brain function to date, these findings are important as marijuana use grows worldwide, the researchers wrote.
More than 1,000 adults ages 22 to 36 participated in the study, providing information about their cannabis use and giving urine samples tested for cannabis concentration. The researchers then used brain imaging technology to track their brain activity while they performed certain tasks. The scans showed that 63% of people who had used cannabis more than 1,000 times — defined as heavy lifetime users — had reduced brain activity during a working memory task. The results were similar for 68% of people who had recently used cannabis.
These results were "statistically significant" and unlikely due to "random chance," researchers said, adding that the age of first cannabis use, alcohol and nicotine use, and demographic variables did not account for the results.
Not using cannabis before engaging in tasks that are cognitively demanding may improve performance, the researchers wrote. But they warned that heavy users who suddenly stop using cannabis could go into withdrawal, which might also impact performance.
"Our findings highlight the need to educate cannabis users about the consequences of recent and heavy lifetime cannabis use on cognitively demanding working memory tasks," the researchers wrote. "Similarly, the association between heavy use and decreased brain function could motivate regular cannabis users to reduce their cannabis use and could encourage treatment."
