Philadelphia, January 22, 2019 People with schizophrenia have a hard time integrating information about a reward—the size of the reward and the probability of receiving it—when assessing its value, according to a study in Biological Psychiatry: Cognitive Neuroscience and Neuroimaging. The inability to integrate the two factors correlated with more severe motivational deficits, suggesting that the impairment may contribute to decreased value placed on a reward, and thus reduced motivation to complete the task required to receive it.
Using a computational model to tease apart components of reward estimation for decision making, the researchers, based at the Maryland Psychiatric Research Center, found that the impaired ability to integrate the size and probability of a reward was primarily caused by a lack of consideration of the reward magnitude.
“The paper is a valuable contribution to the new field of Computational Psychiatry,” said Cameron Carter, MD, Editor of Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, adding that computational models, such as the one used in the study, can lead to new insights into the nature of impaired processing in the brain that forms the basis of symptoms and deficits in mental disorders.
“In this study the authors show that people with schizophrenia, whose motivational deficits lead to much of the social and occupational disability in the illness, perform poorly on reward-based decision making because they fail to compute the expected value of a specific action and instead rely on non-value based information available in the task,” said Dr. Carter.
To assess the information that participants used to make their decision, the researchers developed a learning task that required participants to consider both the size of a reward and the probability of receiving it. Participants were presented with two choices, and asked to select the choice with the highest reward value.
“Using the rewarded learning task, we showed that people with motivational deficits focus too much on how often a reward is presented (i.e., probability), at the cost of learning about the size of the reward (i.e., magnitude). Our mathematical model helped determine that these ‘reward integration’ deficits—that is, an inability to combine information about reward probability and magnitude—were linked to a decreased ability to precisely represent reward value, which is thought to involve a brain area called the orbitofrontal cortex,” said lead author Dennis Hernaus, PhD, now based at Maastricht University, The Netherlands.
Participants with schizophrenia who had motivational deficits did worse when the choice was easier (when the objective value between the choices was larger), indicating that their performance declined as the demands on this brain region to assess value increased.
The findings suggest that the mathematical model used in the study could be useful as a diagnostic tool to help identify motivational deficits in patients. The association between poor motivation and reward integration deficits identified in the study helps explain why problems with motivation arise, and hints at deficits within a specific brain region. The researchers plan to study deficits within this brain region and the link to motivational deficits in future studies using neuroimaging.
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Notes for editors
The article is "Impaired expected value computations in schizophrenia are associated with a reduced ability to integrate reward probability and magnitude of recent outcomes," by Dennis Hernaus, Michael J. Frank, Elliot C. Brown, Jaime K. Brown, James M. Gold, and James A. Waltz (https://doi.org/10.1016/j.bpsc.2018.11.011). It appears in Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, published by Elsevier.
Copies of this paper are available to credentialed journalists upon request; please contact Rhiannon Bugno at BPCNNI@sobp.org or +1 214 648 0880. Journalists wishing to interview the authors may contact Dennis Hernaus at dennis.hernaus@maastrichtuniversity.nl or +31 43 388 3893.
The authors’ affiliations and disclosures of financial and conflicts of interests are available in the article.
Cameron S. Carter, MD, is Professor of Psychiatry and Psychology and Director of the Center for Neuroscience at the University of California, Davis. His disclosures of financial and conflicts of interests are available here.
About Biological Psychiatry: Cognitive Neuroscience and Neuroimaging
Biological Psychiatry: Cognitive Neuroscience and Neuroimaging is an official journal of the Society of Biological Psychiatry, whose purpose is to promote excellence in scientific research and education in fields that investigate the nature, causes, mechanisms and treatments of disorders of thought, emotion, or behavior. In accord with this mission, this peer-reviewed, rapid-publication, international journal focuses on studies using the tools and constructs of cognitive neuroscience, including the full range of non-invasive neuroimaging and human extra- and intracranial physiological recording methodologies. It publishes both basic and clinical studies, including those that incorporate genetic data, pharmacological challenges, and computational modeling approaches. http://www.sobp.org/bpcnni
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