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No evidence was found for long-term deficits in working memory and selective attention in frequent cannabis users after 1 week of abstinence. Nonetheless, frequent cannabis use may affect brain function, as indicated by altered neurophysiological dynamics in the left superior parietal cortex during working memory processing.

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Objective-Early-onset cannabis use has been associated with later (ab)use, mental health problems (psychosis, depression) and abnormal development of cognition and brain function. During adolescence ongoing neurodevelopmental maturation and experience shape the neural circuitry underlying complex cognitive functions such as memory and executive control. Prefrontal and temporal regions are critically involved in these functions. Maturational processes leave these brain areas prone to the potentially harmful effects of cannabis use.Method-We performed a two-site (US and NL; pooled data) functional MRI study with a crosssectional design, investigating the effects of adolescent cannabis use on working memory (WM) and associative memory (AM) brain function in twenty-one abstinent but frequent cannabis using boys (age 13 -19) and compared them with twenty-four non-using peers. Brain activity during WM was assessed before and following rule-based learning (automatization). AM was assessed using a pictorial hippocampal-dependent memory task.Results-Cannabis users performed normally on both memory tasks. During WM assessment cannabis users showed excessive activity in prefrontal regions when a task was novel, whereas automatization of the task reduced activity to the same level in users and controls. No effect of cannabis use on AM-related brain function was found.Conclusions-In adolescent cannabis users the WM system was overactive during a novel task, suggesting functional compensation. Inefficient WM recruitment was not related to a failure in automatization, but became evident when processing continuously changing information. The results seem to confirm the vulnerability of still developing frontal lobe functioning for early-onset cannabis use.

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