Abstinent adolescent marijuana users show altered fMRI response during spatial working memory

Abstract

Marijuana is the most widely used illicit substance among teenagers, yet little is known about the possible neural influence of heavy marijuana use during adolescence. We previously demonstrated an altered functional magnetic resonance imaging (fMRI) activity related to spatial working memory (SWM) among adolescents who were heavy users of after an average of 8 days of abstinence, but the persisting neural effects remain unclear. To characterize the potentially persisting neurocognitive effects of heavy marijuana use in adolescence, we examined fMRI response during SWM among abstinent marijuana-using teens. Participants were 15 MJ teens and 17 demographically similar nonusing controls, ages 16-18. Teens underwent biweekly urine toxicology screens to ensure abstinence for 28 days before fMRI acquisition. Groups performed similarly on the SWM task, but MJ teens demonstrated lower activity in right dorsolateral prefrontal and occipital cortices, yet significantly more activation in right posterior parietal cortex. MJ teens showed abnormalities in brain response during a SWM task compared with controls, even after 1 month of abstinence. The activation pattern among MJ teens may reflect different patterns of utilization of spatial rehearsal and attention strategies, and could indicate altered neurodevelopment or persisting abnormalities associated with heavy marijuana use in adolescence.

1301 – Structural and functional imaging studies in chronic cannabis users: a systematic review of adolescent and adult findings

“…Additionally, cannabis users demonstrated greater performance-related activation in the right basal ganglia, precuneus, postcentral gyrus and bilateral superior parietal lobe [179], again suggesting a compensatory neural effort. Consistent with this, Schweinsburg et al (2008) [180] also found a different pattern of activation in abstinent adolescent cannabis users who performed the SWM task similarly to the control group. Thus, cannabis users demonstrated higher activation in the right parietal cortex but also lower activity in the right dorsolateral prefrontal and occipital cortices [180].…”

“…Consistent with this, Schweinsburg et al (2008) [180] also found a different pattern of activation in abstinent adolescent cannabis users who performed the SWM task similarly to the control group. Thus, cannabis users demonstrated higher activation in the right parietal cortex but also lower activity in the right dorsolateral prefrontal and occipital cortices [180]. Finally, in a cross-sectional study, Schweinsburg et al (2010) [181] compared fMRI responses using the same task among adolescent cannabis users with brief and sustained cannabis abstinence and healthy controls.…”

“…However, the level of performance of the cannabis users on the cognitive tasks employed was generally similar to that of controls [164,165,168,171,174,177], or at least within what may be considered a normal range of test performance. Therefore, these findings may be interpreted as reflecting neuroadaptation, perhaps indicating the recruitment of additional regions as a compensatory mechanism to maintain normal cognitive performance in response to chronic cannabis exposure [151,152,164,166,171,172,175,[179][180][181]183], particularly within the prefrontal cortex area [151,166,168,169,171,181,183]. In this regard, the brain seems able to achieve some degree of reorganization, activating brain regions not usually needed to perform the cognitive task in response to an impaired ability of the normally engaged task network.…”

“…In the present review, although we excluded studies involving subjects with alcohol dependence, some included subjects with alcohol misuse (abuse [145,179] or excessive consumption [150]), or reported differences in alcohol intake parameters to]despite alcohol consumption was within safe limits [143,144,147,156,157,163,164,169,170]. Moreover, given the relatively modest number of studies in the adolescent population, we included four studies which may involve some participants with comorbid alcohol dependence [154,155,180,181]. In all these studies, the interaction of alcohol with cannabis use, as well as its contribution to the brain effects cannot be ruled out.…”

The Influence of Marijuana Use on Neurocognitive Functioning in Adolescents

“…Those with a later age of onset and briefer duration of regular use showed the greatest increase in brain response. This could indicate an inverted U-shaped pattern of activation, such that youths with relatively recent initiation show compensatory increases in activation, while those with more long-term use demonstrate neuroadaptive processes resulting in similar response patterns as controls.In a related fMRI study of 15 28-day abstinent marijuana users and 17 controls, teens performed a spatial working memory task that contrasted 2-back location working memory with simple attention (dot detection) [45]. Relative to controls, marijuana users demonstrated reduced fMRI response to spatial working memory trials in right dorsolateral prefrontal cortex, and increased response in right posterior parietal cortex, despite equivalent behavioral performance between groups.…”