Patients with major depressive disorders (MDD) exhibit social dysfunction, as illustrated by the lower acceptance rate of unfair proposals in the Ultimatum Game (UG) among patients with MDD compared with a control group. However, the underlying mechanisms remain largely unknown. In this study, we explored whether patients with MDD had altered perceptions of fairness or altered perception-behavior linkages compared with the control group, using a multilevel moderated mediation framework. Sixtyeight unmedicated patients with MDD and 55 members of a control group were recruited. Using generalized linear mixed effects models and multilevel structural equation modeling, we investigated the differences in the linkages between fairness level, fairness perception, and acceptance behavior among the two groups playing the UG. The results showed that the patients with MDD had a lower acceptance rate of unfair proposals than the control group. Fairness perception mediated the relationship between fairness level and acceptance behavior for both groups of participants when they played with human proposers but not computer proposers. The mediation effect was stronger among the control group than among the MDD patients. The linkage between fairness perception and acceptance behavior was attenuated among the patients with MDD compared with the control group. In conclusion, MDD patients were impaired in their ability to flexibly adjust acceptance behavior based on fairness perception in social interactions.

Background: Dysfunctional beliefs about the self are common in the development of depressive symptoms, but it remains unclear how depressed patients respond to unfair treatment, both dispositionally and neurally. The present research is an attempt to explore the differences in sensitivity to injustice as a victim and its neural correlates in patients with major depressive disorder (MDD) versus healthy controls. Methods: First episodic, drug-naïve patients with MDD (n = 30) and a control group (n = 30) were recruited to compare their differences in victim sensitivity. A second group of patients with MDD (n = 23) and their controls (n = 28) were recruited to replicate the findings and completed resting-state functional magnetic resonance imaging (fMRI) scanning. Spontaneous brain activity measured by fractional amplitude of lowfrequency fluctuation (fALFF) was used to characterize the neural correlates of victim sensitivity both in patients and in healthy controls. Results: Higher victim sensitivity was consistently found in patients with MDD than healthy controls in both datasets. Multiple regression analysis on the fALFF showed a significant interaction effect between diagnosis and victim sensitivity in the right dorsolateral prefrontal cortex (DLPFC). Conclusions: The patients with MDD show higher sensitivity to injustice as a victim, which may be independent of their disease course. The MDD patients differ from healthy controls in the neural correlates of victim sensitivity. These findings shed light on the linkage between cognitive control subserved by the DLPFC and negative bias towards the self implicated by higher victim sensitivity among the depressed patients.

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Objective Major depressive disorder (MDD) and bipolar disorder (BD) are considered whole‐brain disorders with some common clinical and neurobiological features. It is important to investigate neural mechanisms to distinguish between the two disorders. However, few studies have explored the functional dysconnectivity between the two disorders from the whole brain level. Methods In this study, 117 patients with MDD, 65 patients with BD, and 116 healthy controls completed resting‐state functional magnetic resonance imaging (R‐fMRI) scans. Both edge‐based network construction and large‐scale network analyses were applied. Results Results found that both the BD and MDD groups showed decreased FC in the whole brain network. The shared aberrant network across patients involves the visual network (VN), sensorimotor network (SMN), dorsal attention network (DAN), and ventral attention network (VAN), which is related to the processing of external stimuli. The default mode network (DMN) and the limbic network (LN) abnormalities were only found in patients with MDD. Furthermore, results showed the highest decrease in edges of patients with MDD in between‐network FC in SMN–VN, whereas in VAN–VN of patients with BD. Conclusions Our findings indicated that both MDD and BD are extensive abnormal brain network diseases, mainly aberrant in those brain networks correlated to the processing of external stimuli, especially the attention network. Specific altered functional connectivity also was found in MDD and BD groups, respectively. These results may provide possible trait markers to distinguish the two disorders.