Do reward-processing deficits in schizophreniaspectrum disorders promote cannabis use? An investigation of physiological response to natural rewards and drug cues

Background: Dysfunctional reward processing is present in individuals with schizophrenia-spectrum disorders (SSD) and may confer vulnerability to addiction. Our objective was to identify a deficit in patients with SSD on response to rewarding stimuli and determine whether this deficit predicts cannabis use. Methods: We divided a group of patients with SSD and nonpsychotic controls into cannabis users and nonusers. Response to emotional and cannabis-associated visual stimuli was assessed using self-report, event-related potentials (using the late positive potential [LPP]), facial electromyography and skin-conductance response. Results: Our sample comprised 35 patients with SSD and 35 nonpsychotic controls. Compared with controls, the patients with SSD showed blunted LPP response to pleasant stimuli (p = 0.003). Across measures, cannabis-using controls showed greater response to pleasant stimuli than to cannabis stimuli whereas cannabis-using patients showed little bias toward pleasant stimuli. Reduced LPP response to pleasant stimuli was predictive of more frequent subsequent cannabis use (β = -0.24, p = 0.034). Limitations: It is not clear if the deficit associated with cannabis use is specific to rewarding stimuli or nonspecific to any kind of emotionally salient stimuli. Conclusion: The LPP captures a rewardprocessing deficit in patients with SSD and shows potential as a biomarker for identifying patients at risk of heavy cannabis use.