Do motivation deficits in schizophrenia-spectrum disorders promote cannabis use? An investigation of behavioural response to natural rewards and drug cues

Deficits in incentive motivation are often present in both Schizophrenia Spectrum Disorders (SSD) and substance-use disorders. The current study aims to test whether the presence of such deficits confers vulnerability to cannabis use in individuals with SSD. SSD patients (n=35) and healthy controls (n=35) were each divided into a group with (n=20) and a group without (n=15) current cannabis use disorder. Subjects performed a behavioural task designed for schizophrenia patients in which they could seek exposure to pleasant and cannabis visual stimuli on the basis of internal representations of these stimuli. Intensity of cannabis use was assessed by self-report. SSD patients were significantly less likely than controls to exert effort to try to re-view pleasant stimuli but were not significantly less likely to work to avoid unpleasant stimuli. Lack of response to re-view pleasant stimuli significantly predicted higher subsequent cannabis self-administration in patients but not controls, after controlling for degree of prior exposure to cannabis. Deficits in incentive motivation may be an aspect of SSD which promotes cannabis use in this population.