公平问题是人类长久以来的话题，研究已经证实人们存在着公平偏好。以往公平偏好相关的神经生物学研究所发现的脑区及五羟色胺神经递质系统一直被认为在抑郁症病理生理机制中具有重要作用。因此，公平偏好的特质可能成为抑郁症患者不良社会适应能力的一个重要行为标记。本研究的主要研究目标是探析公平偏好能否作为抑郁症的潜在的行为标记。为了回答这一问题，本文采用基于博弈论的公平偏好研究范式并通过三个研究进行了探索。
研究一采用认知行为学研究方法，通过2 个子研究对不同临床样本的抑郁症患者作为最后通牒游戏回应者的公平决策行为特征进行了初步的探索。研究结果共同发现：抑郁症患者存在社会决策功能异常。具体表现为（1）抑郁症患者的接受率低于正常对照；（2）正常对照更多地接受计算机提出的不公平方案，而患者在人和机两种情境下对不公平方案的接受率之间没有显著差异，即患者不能区分来自不同提议者的不公平分配方案。这一发现为后续从接受率和人机区分这两个指标上寻找抑郁症的潜在行为标记提供了方向和依据。
研究二采用功能磁共振成像技术，研究抑郁症患者异常公平相关博弈行为的神经基础及潜在的影像学生物标记。研究结果发现，抑郁症患者作为最后通牒博弈的回应者其社会决策相关脑区的脑激活模式及脑功能连接模式与正常对照存在差异。具体表现为（1）患者组被试其对方案接受率下降这一行为学异常表现存在相应的神经基础：右侧MFG 激活减弱、左侧Insula/ACC 脑-行为失偶联、右侧Insula-ACC 功能网络失偶联、及代偿性连接增强这些异常的脑激活模式和脑功能连接模式可能是其背后的神经机制；（2）患者组被试未能对人机提议者进行区别对待这一行为学异常表现存在相应的神经基础：左侧MPFC 脑-行为失偶联这一异常的脑功能活动可能是其背后的神经机制。该结果表明行为学研究中发现的抑郁症患者两点异常的公平决策行为模式（即：对方案接受率的下降及不能区分人机差异）存在其相应的神经基础，这些异常的脑激活模式及脑功能连接模式可能是抑郁症患者潜在的影像学生物标记。
然而，一个指标能否作为生物学标记，其核心标准之一是该指标是否具有遗传性。因此，研究三采用双生子研究，探索了人们在最后通牒博弈中的行为表现和脑功能活动是否存在相应的遗传基础。研究结果表明：（1）最后通牒博弈回应者对方案的接受率这个指标有中等程度的遗传基础，遗传因素在其中的贡献比率约为34%，这一发现为将最后通牒博弈中的方案接受率作为抑郁症的潜在行为标记提供了依据；（2）我们没有发现人机提议者间决策差异有显著的遗传基础，因而其能否作为抑郁症的潜在行为标记还有待确定；（3）影像遗传学基于感兴趣区和基于体素的分析结果共同发现双侧脑岛这一在公平相关决策中至关重要的脑区也有中等程度的遗传基础，结合研究二抑郁症的影像分析结果，双侧脑岛的脑功能活动可能可以作为抑郁症的潜在生物学标记。根据前人提出的关于生物学标记或内表型必须是可遗传的这一标准，本研究的发现为公平偏好作为抑郁症的潜在行为标记提供了直接的证据。
总之，本文基于最后通牒博弈，从行为实验，到影像学研究，再到双生子研究，逐层深入地揭示了公平偏好的特质可能作为抑郁症患者不良社会适应能力的一个重要行为标记，抑郁症患者对方案接受率的下降和双侧脑岛的脑功能活动异常是其异常公平偏好行为的重要指标。本文的研究结果发现的抑郁症的潜在行为标记，或可将其应用于抑郁症的心理社会干预和康复计划中，改善其治疗方式，从而改善抑郁患者的社会认知和社会适应能力，促进其回归社会。

Fairness has long been a topic of human society, and numerous studies confirm that people have fairness preference. Previous neurobiology researches have found that some brain regions and serotonin neurotransmitter systems play significant roles in fairness-related social behavior, and these brain regions and serotonin neurotransmitter systems have been considered to play important roles in the pathophysiology of major deoressive disorder (MDD). Therefore, the trait of fairness preference may be an important behavioral marker of maladaptation of MDD. The main objective of this study was to investigate whether fairness preference is a potential behavioral marker of MDD. To answer this question, the present thesis utilized a game theory paradigm which is often used to examine fairness preference and carried out three studies.
In Study 1, by using cognitive-behavioral research methods, we explored the characteristics of fairness-related social decision-making behavior of MDD patients who played as responders in the Ultimatum Game (UG). This study included two substudies which have different clinical samples. Both substudies found that depressed patients show abnormal decision-making behavior in a social interaction context. Specifically, (1) the acceptance rates of the patients were lower than those of the normal controls; (2) unfair proposals were accepted at similar rates from computer partners and human partners in the MDD patients, unlike the acceptance rates in the normal controls, who were able to discriminatively treat unfair proposals from computer partners and human partners. These findings light up direction and provide the basis for further investigation of MDD patients’ potiential behavioral markers from the point of acceptance rate and human-computer indiscrimination.
In Study 2, by using functional magnetic resonance imaging (fMRI), we explored the neural basis of abnormal fairness preference behaviors in MDD and the potential biomarkers. This study found that the brain activation pattern and the brain functional connectivity pattern of MDD patients were different from the normal controls when playing the UG. Specifically, (1) there are neural basis for the abnormal behavior of decreased acceptance rate in MDD. Abnormal brain activation patterns and brain functional connectivity patterns, such as decreased activation of the right MFG, brain activation-behavior uncoupling of the left insula and ACC, functional network uncoupling of the right insula-ACC, and enhanced compensatory connectivities, may be the potiential neural mechanisms; (2) there are neural basis for the abnormal behavior of human-computer indiscrimination in MDD. Brain activation-behavior uncoupling of the right insula may be the potiential neural mechanisms. These results showed that there are neural basis for the two abnormal behavioral patterns found in Study 1, i.e., decreased acceptance rate and human-computer indiscrimination. These abnormal brain activation patterns and brain functional connectivity patterns may be the potiential biomarkers of MDD patients.
However, whether a characteristic can be a biomarker, the core standard is that the characteristic must be heritable. Thus, in Study 3, by using twin studies, we explored whether there are genetic bases for the behavior performance and brain activity in the UG. This study found that (1) the acceptance rate of the responder in the UG were moderately heritable (34.0%), which provides a basis for acceptance rate in the UG as a potential marker of MDD; (2) the genetic basis of the decision differences between human and computer proposers was not found, thus whether this behavior can be a potential marker of MDD has yet to be determined; (3) ROI-based and voxel-based analysis of the fMRI data both showed that the activations of the bilateral insula which is crucial in the fairness-related decision-making also have moderately genetic basis, which indicated that brain activity of the bilateral insula may act as potential biomarkers of MDD. According to the proposed standard that biomarkers or endophenotype must be heritable, the findings in this study has provided direct evidence for the fairness preference as a potential marker of MDD.
Taken together, this study indicated that fairness preference is a potiential marker of major depressive disorder. Decreased acceptance rate and abnormal brain activation in bilateral insula are significant indeces of altered fairness preference behavior in MDD. These new potential behavioral markers may be used for early diagnosis and prognosis for MDD, and also for the psychosocial intervention and rehabilitation programs of MDD. This can further help to improve their treatment, thereby improve the social cognition and social adaptability of MDD, ultimately promote their return to society.