Clifford M. Cassidy, PhD; Mathieu B. Brodeur, PhD; Martin Lepage, PhD; Ashok Malla, MD
Cassidy, Brodeur, Lepage, Malla — Department of Psychiatry, McGill University, Montréal, Que., Canada; Cassidy — Department of Psychiatry, Columbia University, New York, NY, USA
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.
Submitted Sept. 15, 2013; Revised Jan. 5, Jan. 17, 2014; Accepted Jan. 20, 2014; Early-released June 10, 2014.
Acknowledgements: This work was supported by a doctoral research award from the Canadian Institutes of Health Research (C. Cassidy). A. Malla is funded through the Canada Research Chair program. We thank PEPP staff, members of the Brodeur and Lepage laboratories, Joseph Rochford and Norbert Schmitz for assistance.
Competing interests: None declared.
Contributors: All authors designed the study. C.M. Cassidy and M. Brodeur acquired the data, which all authors analyzed. C.M. Cassidy wrote the article, which all authors reviewed and approved for publication.
Correspondence to: C. Cassidy, Department of Psychiatry, Columbia University, New York State Psychiatry Institute, 1051 Riverside Dr., New York, NY, 10032; firstname.lastname@example.org