Anhedonia and amotivation are common symptoms in patients with schizophrenia, major depressive disorder and bipolar disorder, suggesting a necessity to explore the underlying behavioural and neural mechanisms to facilitate the development of effective therapeutic programmes and social function rehabilitation. Accumulating evidence indicated that the nature of anhedonia may not be only due to deficits in pleasure experience or reward pursuit motivation, but may also be related to failure in translating emotional salience into effortful behaviour. Most of the previous studies were mainly limited to behavioural measures and examination of patients with only one diagnostic group without comparing to other mental disorders. Dr. Raymond Chan and his team from the Neuropsychology and Applied Cognitive Neuroscience Laboratory, CAS Key Laboratory of Mental Health, Institute of Psychology has recently showed that although patients with schizophrenia, major depressive disorder and bipolar disorder all exhibit a lowered capacity to experience pleasure as well as a lack of motivation, the pattern of emotion-behaviour dissociation is different across these patients.
To-date, however, no neuroimaging study has been done to compare and contrast the neural mechanisms underlying the observed anhedonia and amotivation in patients with schizophrenia, major depressive disorder and bipolar disorder. In order to bridge such a gap, Dr. Chan and his team has conducted a study to examine the neural correlates of effort-expenditure for reward across these three groups of patients. They recruited 20 schizophrenia patients, 23 major depressive patients, 17 bipolar disorder patients, and 30 healthy controls to complete an Effort-Expenditure for Reward Task (EEfRT) inside a 3T brain scanner. The task used an event-related design and consisted of 6 conditions, through the crossing of reward magnitude (low, high) with reward probability (20%, 50%, 80%). The ratio of high-effort tasks chosen under different probabilities reflects a participant’s motivation to pursue rewards.
Their results showed that the three patients groups exhibited shared activations in the cingulate gyrus, the medial frontal gyrus and the middle frontal gyrus during the EEfRT administration. Patients with schizophrenia showed stronger variations of functional connectivity between the right caudate and the left amygdala, the left hippocampus and the left putamen, with increase in reward magnitude comparing to healthy controls. Patients with major depressive disorder exhibited an enhanced activation compared to healthy controls in the right superior temporal gyrus when there was an increase of reward magnitude. The variations of functional connectivity between the caudate and the right cingulate gyrus, the left postcentral gyrus and the left inferior parietal lobule with increase in reward magnitude were weaker than that found in healthy controls. Patients with bipolar disorder exhibited an increased activation in the left precuneus but a decreased activation in the left dorsolateral prefrontal cortex when there was an increase in reward probability compared to healthy controls. Taken together, these findings demonstrate patients with schizophrenia, major depressive disorder and bipolar disorder exhibit both shared and distinct neural mechanisms associating with effort-based decision-making. These findings may have potential important implications for the development of neuro-modulation intervention to alleviate anhedonia and amotivation in these disorders.
This study was supported by grants from the National Key Research and Development Programme, the National Science Fund China, the Beijing Municipal Science & Technology Commission Grant, the Beijing Training Project for the Leading Talents in Science and Technology, the Philip K. H. Wong Foundation, the CAS Key Laboratory of Mental Health, Institute of Psychology, the Natural Science Foundation of Shandong Province, and the Humanities and Social Sciences Research Project of Ministry of Education.
This study entitled "Shared and distinct reward neural mechanisms among patients with schizophrenia, major depressive disorder, and bipolar disorder: an effort-based functional imaging study" is now available online on 26 January 2022 from European Archives of Psychiatry and Clinical Neuroscience.
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