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Individuals with many different psychiatric disorders have a higher tendency to choose smaller, immediate rewards over larger, delayed rewards, a study led by Hamilton researchers has found.

The findings of a meta-analysis by researchers of McMaster University and St. Joseph’s Healthcare Hamilton, which combined data from more than 40 studies, were published in JAMA Psychiatry.

That this type of decision-making tied to impulsivity, called delay discounting, is heightened in those with certain psychiatric disorders compared to others, is expected to have an important impact on future research and treatment across an array of disorders.

“The revelation that delay discounting is one of these ‘trans-diagnostic’ processes will have a significant effect on the future of psychiatric diagnosis and treatment,” said Michael Amlung, lead author of the study. He is an assistant professor of psychiatry and behavioural neurosciences at McMaster University and researcher for the Peter Boris Centre for Addictions Research at St. Joseph’s Healthcare Hamilton.

The study analyzed data from studies across eight different psychiatric disorders, including major depressive disorder, bipolar disorder, borderline personality disorder, schizophrenia, eating disorders, and others. The largest delay discounting effects were found to be associated with bipolar disorder, borderline personality disorder, and schizophrenia.

Previous research has linked a greater preference for immediate rewards and impulsivity to negative health outcomes, such as addiction, obesity, and ADHD. This study reinforced that negative association, finding that impulsive preferences are consistently observed across an even broader range of psychiatric disorders.

Interestingly, the study also found the opposite pattern in those with anorexia nervosa. The researchers explained that the greater preference for delayed over immediate rewards seen in people with anorexia is consistent with excessive self-control of their eating habits.

The study authors say this pattern suggests that delay discounting preferences are best thought of as being on a continuum, with some disorders exhibiting excessively impulsive decisions and other disorders exhibiting excessively self-controlled decisions.

“Examining factors that cut across psychiatric disorders, such as delay discounting, helps to illuminate commonalities and distinguishing characteristics amongst disorders that then guide further research on treatment and prevention,” said Randi McCabe, co-author of the paper, psychologist-in-chief at St. Joseph’s Healthcare Hamilton and professor of psychiatry and behavioural neurosciences at McMaster.

“The more we understand the nature of psychiatric illness, the better we are equipped to provide effective treatment strategies,” she said.

The authors say the study findings support the inclusion of delay discounting in the Research Domain Criteria (RDoC) framework proposed by the National Institute of Mental Health, as a potent indicator of psychiatric illness. RDoC is a biologically-valid framework for understanding mental disorders, and includes research approaches in genetics, neuroscience, and behavioural science.

“Our results provide strong evidence for delay discounting as a core behavioural process within the RDoC framework,” Amlung said. “On a broader level, this study underscores the need for future research examining common neurobiological and genetic underpinnings of this type of decision making in order to inform evidence-based treatments across psychiatric disorders.”

A unique strength of this research was the interdisciplinary team of authors that included behavioural scientists, clinical psychologists, graduate students, and research staff from St Joe's, McMaster, and the University of Kansas.

By training the next generation of outstanding mental health and addictions scientists, the study also embodied St. Joe’s commitment and vision to educating the world’s best.

“A meta-analysis of this scale requires far more than my efforts as lead author,” noted Amlung. “Conducting this study required a tremendous effort from a large group of people to locate and select studies, extract data, and generate the results. I am especially proud that this project allowed me to engage my graduate students and research assistants in high-impact psychiatry research.”

The Peter Boris Centre for Addictions Research, a partnership of St. Joseph’s Healthcare Hamilton and McMaster University, partially funded this study.

“Since the creation of the Peter Boris Centre for Addictions Research five years ago, the incredible work of our research faculty has given the Centre an international reputation for excellence,” said Dr. Gail Martin, Executive Director of the Research Institute of St. Joe’s. “This study is further proof of this high-quality mental health and addictions research that is characteristic of the Research Institute.”

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