Chronic cannabis use differentially modulates neural oscillations serving the manipulate versus maintain components of working memory processing.

Heavy cannabis users show weaker alpha brain oscillations during the encoding phase of a working memory task, particularly in superior parietal and occipital regions, compared to nonusers. During memory maintenance, a group-by-condition interaction emerged: cannabis users exhibited weaker alpha and beta oscillations during maintain trials but stronger oscillations in the same regions during manipulate trials, alongside prolonged reaction times. Nonusers showed no such differences. Neurobehavioral relationships in prefrontal cortices appeared only in nonusers. Chronic cannabis use may impair initial memory encoding but prompt compensatory neural activity during more demanding memory manipulation.

Study at a glance

Abstract

The legalization of recreational cannabis use has expanded the availability of this psychoactive substance in the United States. Research has shown that chronic cannabis use is associated with altered working memory function, however, the brain areas and neural dynamics underlying these affects remain poorly understood. In this study, we leveraged magnetoencephalography (MEG) to investigate neurophysiological activity in 45 participants (22 heavy cannabis users) during a numerical WM task, whereby participants were asked to either maintain or manipulate (i.e., rearrange in ascending order) a group of visually presented numbers. Significant oscillatory responses were imaged using a beamformer and subjected to whole-brain ANOVAs. Notably, we found that cannabis users exhibited significantly weaker alpha oscillations in superior parietal, occipital, and other regions during the encoding phase relative to nonusers. Interestingly, during the maintenance phase, there was a group-by-condition interaction in the right inferior frontal gyrus, left prefrontal, parietal, and other regions, such that cannabis users exhibited weaker alpha and beta oscillations relative to nonusers during maintain trials. Additionally, chronic cannabis users exhibited stronger alpha and beta maintenance responses in these same brain regions and prolonged reaction times during manipulate relative to maintain trials, while no such differences were found in nonusers. Neurobehavioral relationships were also detected in the prefrontal cortices of nonusers, but not cannabis users. In sum, chronic cannabis users exhibit weaker neural oscillations during working memory encoding but may compensate for these deficiencies through stronger oscillatory responses during memory maintenance, especially during strenuous tasks such as manipulating the to-be remembered items.