Public perception of cannabis as relatively harmless, alongside claimed medical benefits, have led to moves towards its legalization. Yet, long-term consequences of cannabis dependence, and whether they differ qualitatively from other drugs, are still poorly understood. A key feature of addictive drugs is that chronic use leads to adaptations in striatal reward processing, blunting responsivity to the substance itself and natural (non-drug) rewards. Against this background, the present study investigated whether cannabis dependence is associated with lasting alterations in behavioral and neural responses to social reward in 23 abstinent cannabis-dependent men and 24 matched non-using controls. In an interpersonal pleasant touch fMRI paradigm, participants were led to believe they were in physical closeness of or touched (CLOSE, TOUCH) by either a male or female experimenter (MALE, FEMALE), allowing contextual modulation of the perceived pleasantness and associated neural responses. Upon female compared to male touch, dependent cannabis users displayed a significantly attenuated increase of pleasantness experience compared to healthy controls. Controls responded to female as compared to male interaction with increased striatal activation whereas cannabis users displayed the opposite activation pattern, with stronger alterations being associated with a higher lifetime exposure to cannabis. Neural processing of pleasant touch in dependent cannabis users was found to be intact. These findings demonstrate that cannabis dependence is linked to blunted striatal processing of non-drug rewards and suggest that these alterations may contribute to social processing deficits.
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