Masahiro Takamura1, Yasumasa Okamoto2, Go Okada1, Shigeru Toki3, Tetsuya Yamamoto4, Naho Ichikawa1, Asako Mori1, Hideaki Minagawa5, Yoshiyuki Takaishi6, Yasutaka Fujii7, Yoko Kaichi8, Yuji Akiyama9, Kazuo Awai8, Shigeto Yamawaki1. 1. Department of Psychiatry and Neurosciences, Institute of Biomedical and Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan. 2. Department of Psychiatry and Neurosciences, Institute of Biomedical and Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan. Electronic address: oy@hiroshima-u.ac.jp. 3. Daijikai Mihara Hospital, 6-31-1, Nakano-cho, Mihara, Hiroshima 723-0003, Japan. 4. Graduate School of Integrated Arts and Sciences, Tokushima University, 1-1, Minamijosanjima-cho, Tokushima 770-8502, Japan. 5. Hiroshima City Mental Health and Welfare Center, 11-27 Fujimi-cho, Naka-ku, Hiroshima, Hiroshima 730-0043, Japan. 6. Department of Psychiatry, Yoshida General Hospital, Yoshida-cho Yoshida, Akitakata, Hiroshima 731-0595, Japan. 7. Fujii Psychosomatic Clinic, 10-18, Teppo-cho, Naka-ku, Hiroshima, Hiroshima 730-0017, Japan. 8. Department of Diagnostic Radiology, Institute of Biomedical and Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan. 9. Department of Clinical Radiology, Hiroshima University Hospital, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan.
Abstract
BACKGROUND: Anhedonia is a core symptom of major depressive disorder (MDD). While recent evidence suggests that reduced motivation for reward may be a core feature of anhedonia, the abnormalities in modulatory neural responses to variable reward amounts in MDD patients remain unclear. We investigated whether MDD patients' ability to represent variable-sized monetary rewards in the striatum is disrupted. METHODS: Twelve MDD patients and 12 healthy volunteers completed an assessment of psychometric status and participated in a functional magnetic resonance imaging (fMRI) task that involved the anticipation of financial reward (monetary incentive delay task). The size of the monetary reward was varied among trial conditions and was cued with geometric stimuli. Patients participated in additional fMRI sessions after a 6-week pharmacological treatment with escitalopram, an SSRI. RESULTS: In healthy volunteers, striatal activity increased in proportion to the size of the monetary reward during reward anticipation. This pattern was altered in MDD patients, and significant group-by-reward size interaction effects were observed in the bilateral putamen and the left ventral striatum. Reward sensitivity in motor response and striatum activity at three regions were correlated in healthy controls. In MDD patients, this neurobehavioral coupling was not observed. In addition, changes in the neural reward sensitivity parameter at the left ventral striatum in response to treatment were positively correlated with a reduction of depressive symptoms. CONCLUSIONS: Patients with MDD exhibit reduced ability to modulate neural response when adjusting for variable amount of reward. This result suggests that reward size coding in the striatum may represent a neural correlate of motivational anhedonia in MDD patients.
BACKGROUND: Anhedonia is a core symptom of major depressive disorder (MDD). While recent evidence suggests that reduced motivation for reward may be a core feature of anhedonia, the abnormalities in modulatory neural responses to variable reward amounts in MDDpatients remain unclear. We investigated whether MDDpatients' ability to represent variable-sized monetary rewards in the striatum is disrupted. METHODS: Twelve MDDpatients and 12 healthy volunteers completed an assessment of psychometric status and participated in a functional magnetic resonance imaging (fMRI) task that involved the anticipation of financial reward (monetary incentive delay task). The size of the monetary reward was varied among trial conditions and was cued with geometric stimuli. Patients participated in additional fMRI sessions after a 6-week pharmacological treatment with escitalopram, an SSRI. RESULTS: In healthy volunteers, striatal activity increased in proportion to the size of the monetary reward during reward anticipation. This pattern was altered in MDDpatients, and significant group-by-reward size interaction effects were observed in the bilateral putamen and the left ventral striatum. Reward sensitivity in motor response and striatum activity at three regions were correlated in healthy controls. In MDDpatients, this neurobehavioral coupling was not observed. In addition, changes in the neural reward sensitivity parameter at the left ventral striatum in response to treatment were positively correlated with a reduction of depressive symptoms. CONCLUSIONS:Patients with MDD exhibit reduced ability to modulate neural response when adjusting for variable amount of reward. This result suggests that reward size coding in the striatum may represent a neural correlate of motivational anhedonia in MDDpatients.