The present study aims to identify neural mechanisms related to brain reward function in schizophrenia and comorbid cannabis use disorder (SCZ-CUD) by examining their fMRI activity during reward anticipation.

CUD is present in up to 42% of patients with SCZ. Cannabis use worsens symptoms of psychosis and disease prognosis, yet patients with SCZ-CUD continue to use the drug. Previous research has demonstrated impaired brain reward function in SCZ. We previously hypothesized that use of cannabis may remediate impaired brain reward function in this population, a form of self-medication, yet few studies have examined reward function in this comorbid group. A better understanding of the brain reward-related neural mechanisms in SCZ-CUD may support this self-medication hypothesis and lead to the development of safe and effective treatments.

Using fMRI, we assessed 34 abstinent patients with SCZ-CUD, 51 abstinent CUD-only patients (without SCZ), 18 SCZ-only patients (without CUD) and 28 healthy controls during a Monetary Incentive Delay task. Group differences in activity during reward anticipation were examined through voxel-wise whole-brain analyses.

For reward contrasts, SCZ-CUD patients showed greater task-related activity compared to healthy controls in a cluster including the right parahippocampal gyrus and the cingulate gyrus (cluster size = 1000). SCZ-CUD patients also showed increased activity compared to SCZ-only patients in a cluster consisting of the precuneus, posterior cingulate, and the limbic lobe (cluster size = 529). For reward magnitude contrasts, SCZ-CUD patients showed significantly decreased activity compared to CUD-only group in the cingulate gyrus (cluster size = 280).

This whole-brain study presents evidence for atypical task-related activity in areas related to reward processing during reward anticipation in SCZ-CUD patients compared to healthy controls and SCZ-only patients. Future research will examine the impact of consumption of cannabis on brain reward function, which may inform the development of targeted treatments for patients with SCZ-CUD.