Abstract
Cannabis has been associated with deficits in memory performance. However, the neural correlates that may underpin impairments remain unclear. We carried out a systematic review of functional magnetic resonance imaging (fMRI) studies investigating brain functional alterations in cannabis users (CU) compared to nonusing controls while performing memory tasks, complemented with focused narrative reviews of relevant preclinical and human studies. Twelve studies employing fMRI were identified finding functional brain activation during memory tasks altered in CU. Memory performance studies showed CU performed worse particularly during verbal memory tasks. Longitudinal studies suggest that cannabis use may have a causal role in memory deficits. Preclinical studies have not provided conclusive evidence of memory deficits following cannabinoid exposure, although they have shown evidence of cannabinoid-induced structural and histological alteration. Memory performance deficits may be related to cannabis use, with lower performance possibly underpinned by altered functional activation. Memory impairments may be associated with the level of cannabis exposure and use of cannabis during developmentally sensitive periods, with possible improvement following cessation of cannabis use.
Highlights
Cannabis is the most-used illicit drug worldwide [1], with many beginning to use it during their adolescent years [2,3]
Memory performance deficits may be related to cannabis use, with lower performance possibly underpinned by altered functional activation
Cannabis use has been shown in some studies to negatively affect memory-related brain functioning and task performance, verbal memory and encoding in human studies, with preclinical evidence generally consistent with human evidence
Summary
Cannabis is the most-used illicit drug worldwide [1], with many beginning to use it during their adolescent years [2,3]. Acute effects of the drug have been shown on cognitive performance, in the domain of memory [4], with impairments being observed in all aspects of memory function, such as encoding, storage, and recall [5,6]. In addition to evidence about its acute effects, meta-analytic evidence has documented that long-term use of cannabis is associated with memory deficits [7]. Brain-structural alterations in cannabis users have been previously attributed to underlie deficits in memory performance. Cannabis users have shown volume reductions in the medial temporal cortex, in the parahippocampal gyrus and temporal pole [14], as well as decreased cortical thickness in the orbital frontal cortex [14,15,16,17], Brain Sci. 2020, 10, 102; doi:10.3390/brainsci10020102 www.mdpi.com/journal/brainsci
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