父母躯体虐待（physical maltreatment）是指父母对儿童实施的严重身体攻击行为，其严重程度超出了通常所认为的管教儿童的正常范围，对儿童有伤害风险，如对儿童拳打脚踢，掐脖子等。遭受虐待被公认为是早期逆境（early adversity；即童年期创伤性经历和消极成长环境）的核心指标之一，会对儿童发展和适应产生严重的不良影响，因此备受心理学研究者的关注。 尽管研究者围绕着父母躯体虐待与儿童行为适应之间的关系开展了一系列的实证研究，且获得了一些重要的研究成果。然而，相比于国外积累多年的有关父母躯体虐待影响儿童发展的丰富研究成果，国内相关领域的研究尚处于起步阶段，缺少整合性的理论模型，且已有研究较为零散，缺乏系统性。 首先，国内关于父母躯体虐待与儿童外化问题行为之间关系的研究大多为横断研究，缺少纵向追踪数据，难以推断二者之间的因果关系。第二，已有相关研究大多考察父母躯体虐待与儿童外化问题行为之间的直接关系，而对于二者之间的具体作用机制知之甚少。随着理论和研究手段的发展，该领域的研究也在不断深入，近年来国外研究者越来越多地借助生物学和神经科学的方法，开始探究包括父母躯体虐待在内的早期逆境与儿童发展之间的作用机制，试图理解早期的消极环境因素是如何通过关键的内在生理过程（“get under the skin”）影响儿童的行为适应结果。其中，应激系统（包括生理系统和情绪系统），尤其是生理应激系统的作用在早期逆境和儿童行为问题研究领域，受到越来越多研究者的关注。而目前国内父母躯体虐待领域更多关注心理行为层面的研究，探究内在生理机制的研究尚少。第三，已有相关研究大多将父母躯体虐待视为一个单一指标，关注整体父母躯体虐待的作用，较少考虑不同的躯体虐待指标和特征的作用，例如是否受虐待和虐待严重程度，以及父亲躯体虐待和母亲躯体虐待。最后，现有的父母躯体虐待与儿童外化问题行为之间关系及作用机制的结论主要源于西方文化背景下的研究，是否适用于中国文化背景尚不明确。 针对上述问题，本研究拟结合追踪问卷调查、日常自然情境动态测量和实验室急性心理应激测试等多种研究方法和研究范式，深入探讨父母躯体虐待与儿童外化问题行为之间的关系及其生理和情绪机制。研究一采用追踪研究考察父母躯体虐待对儿童外化问题行为的直接影响，并验证二者之间的因果关系，为后续考察二者之间的作用机制奠定基础。研究二和研究三考察父母躯体虐待和儿童外化问题行为之间的作用机制，本论文聚焦于与应激和儿童行为适应均密切相关的生理（下丘脑-垂体-肾上腺皮质（hypothalamic-pituitary-adrenocortical, HPA）轴）和情绪系统的作用。由于HPA轴的基础活动性和应激下反应性，可能反映了HPA轴功能的不同侧面，且均对维持和调节机体的正常运转和身心健康具有重大意义。因此，研究二先考察父母躯体虐待与儿童在日常“基础条件”下的HPA轴活动性（以基础皮质醇为指标）和情绪体验的关系，以及这种基础活动性的异常是否会预测儿童的外化问题行为。研究三则进一步考察父母躯体虐待与儿童在实验室“应激条件”下的HPA轴反应（以皮质醇反应为指标）和情绪反应的关系，以及这种反应功能的异常是否会预测儿童的外化问题行为。对上述问题的探讨，能够回答在基础和急性应激两种不同的条件下，受躯体虐待儿童的HPA轴活动性异常是否表现出一致的方向。同时，也有助于更全面和深入地理解父母躯体虐待与儿童行为适应问题之间关系的生理和情绪通路。 研究一采用纵向设计，实施两次问卷调查，在1099名儿童（10.82±0.89岁）中考察父母躯体虐待的发生率，以及父母躯体虐待对儿童外化问题行为的影响，并采用交叉滞后模型验证二者之间的因果关系，为后续研究做铺垫。结果发现，父母躯体虐待现象较为普遍，有40.9%的儿童在基线时报告曾经受过父母躯体虐待；父母躯体虐待是儿童外化问题行为的重要且稳定的预测因素（反之则不然），且在排除了人口学变量和其他负性生活事件后依然显著。此外，上述预测作用不存在显著的儿童性别差异。 研究二采用日常自然情境中多日重复测量和问卷调查相结合的方法，分别考察父亲和母亲躯体虐待、儿童日常基础皮质醇和日常消极情绪、以及儿童外化问题行为之间的关系（N=111，10.78±0.93岁）。结果发现，以日常皮质醇分泌总量为HPA轴基础活动性的指标能揭示受躯体虐待儿童的生理应激系统机能障碍，体现为HPA轴基础活动性不足。此外，儿童的日常皮质醇分泌总量偏低能在父亲和母亲躯体虐待与儿童外化问题行为之间起到中介作用，而日常消极情绪水平的中介作用则不显著。 研究三采用实验室应激测试和问卷调查相结合的方法，分别考察父亲和母亲躯体虐待、儿童应激下皮质醇反应和消极情绪反应、以及儿童外化问题行为之间的关系（N=138，10.67±0.94岁）。结果发现，以皮质醇分泌总量为应激下HPA轴活动性的指标，也能够揭示受躯体虐待儿童的生理应激系统机能障碍，体现为应激下HPA轴反应不足，皮质醇分泌偏少，而情绪系统的机能障碍则体现为应激下消极情绪过度强烈。此外，儿童在应激下的皮质醇分泌总量偏低和消极情绪总体水平偏高均能在父亲和母亲躯体虐待与儿童外化问题行为之间起到中介作用。 本研究有效地结合了多种研究范式，首次在中国文化背景下较为细致、深入地探讨了父母躯体虐待与儿童外化问题行为之间的关系及其生理和情绪机制。结果表明，父母躯体虐待是儿童外化问题行为的稳定预测因素，反之则不然；基础皮质醇水平偏低和应激下皮质醇反应不足，以及应激下消极情绪反应过度均能在父母躯体虐待与儿童外化问题行为之间起中介作用。此外，在基础和急性应激两种不同的条件下，受躯体虐待儿童的HPA轴功能异常表现出一致的方向，即均为活动性不足。在应激条件下，受躯体虐待儿童的生理反应和情绪反应表现出一定程度的差异性（生理反应不足，而情绪反应过度）。本论文的研究结果，有利于丰富父母躯体虐待与儿童发展领域的理论研究，同时，也能够为儿童虐待领域的预防和干预实践工作提供的科学依据。

Parental physical maltreatment refers to parents’ acts of severe physical aggression (e.g., punching, kicking, burning) to inflict pain on their children, which is more severe than that allowed by laws for disciplining children. Exposure to childhood physical maltreatment, which, being regarded as one of the early adversities, is linked to elevated externalizing behavior problems across development. It is critical to identify mechanisms that explain the link between physical maltreatment and behavioral problems, as such mechanisms may serve as targets for early intervention efforts. As research on early adversity, stress biology, and child development has grown exponentially in recent years, activity and regulation of stress responses (both biological and emotional responses) are widely viewed as key mechanisms through which early adversity ‘gets under the skin’ to impact physical and mental health. However, only a small literature demonstrates that alterations in activity of these systems mediate between adverse conditions and poor outcomes in children and adolescents. It is still far from understanding the various pathways through which adversity ‘gets under the skin’ to influence stress and development. Several other limitations of the previous studies in this field which are also worthy of further investigation. First, most of the previous research which explored the relationship between parental physical maltreatment and children’s externalizing behavior problems in China was cross-sectional, thus it could not draw ?rm conclusions about causality. Second, the existing research has mainly regarded the parental physical maltreatment as a single variable, without further investigating the individual effects of different maltreatment characteristics, such as paternal maltreatment versus maternal maltreatment. Final, the existing conclusions about the effects of parental physical maltreatment on child development are mostly based on the research in Western countries, while much less is known about these associations in Chinese children. Thus, this dissertation aimed to examine the associations among parental physical maltreatment, activity and regulation of stress response systems (cortisol and negative emotion), and children’s externalizing behavior. To mainly answer whether daily basal cortisol levels and negative emotion levels, as well as stress-induced cortisol and emotional responses could explain the association between parental physical maltreatment and children’s externalizing behavior. Study 1: This study aimed to investigate the direct effect of parental physical maltreatment on children’s externalizing problem behavior six months later, as well as to identify the causal relations between parental physical maltreatment and children’s externalizing problem behavior to lay foundation for the following two mechanism studies. A sample of 1099 children (10.82±0.89 years) completed measures of their parental physical maltreatment toward them and their own externalizing problem behavior at two time points (baseline survey and 6 months later). The findings revealed that: (1) The lifetime prevalence of parental physical maltreatment in the current sample was 40.9%. (2) Parental physical maltreatment significantly predicted children’s externalizing problem behavior 6 months later, but not vice versa. These associations remained significant after adjusting for covariates and other stressful life events, and did not vary by children’s gender. Study 2: This study aimed to examine whether dysregulation of daily basal cortisol concentration as well as daily negative emotion explained the association between parental physical maltreatment and externalizing problem behavior in childhood. A sample of 111 children (10.78±0.93 years) were recruited in Beijing, China. A multiple-day naturalistic salivary cortisol protocol was used. Cortisol samples were collected at morning and afternoon across 3 days at school. Also, at each day when children provided afternoon saliva samples, they were asked to rate how often they experienced each of the 6 negative feelings during the day. Also, children completed measures of their paternal and maternal physical maltreatment toward them separately and children’s externalizing problem behavior were rated by one of their parents. Results showed that: (1) Both paternal and maternal physical maltreatment were associated with children’s lower basal cortisol (hypoactivity of the HPA axis), as indexed by the lower total cortisol concentration (area under the curve with respect to ground, AUCg) at the daytime, which in turn led to elevated externalizing behavior. The indirect effects of parental physical maltreatment on externalizing behavior through lower basal cortisol were significant. (2) In contrast, the indirect effects of parental physical maltreatment on externalizing behavior through daily negative emotion were non-significant. Study 3: This study aimed to examine whether dysregulation of cortisol and emotional responses to stress explained the association between parental physical maltreatment and children’s externalizing problem behavior. A sample of 138 children (10.67±0.94 years) were recruited in Beijing, China. The Trier Social Stress Test for Children (TSST-C) protocol was used. A total of six segments of salivary samples and subjective stress measures were obtained throughout the test. The measurements of parental physical maltreatment and children’s externalizing problem behavior are the same as those in Study 2. Results showed that: (1) Both paternal and maternal physical maltreatment were associated with children’s blunted cortisol stress responses, as indexed by the lower total cortisol concentration (AUCg) over the course of TSST-C, which in turn led to elevated externalizing behavior. The indirect effects of parental physical maltreatment on externalizing behavior through blunted cortisol response were significant. (2) In contrast, both paternal and maternal physical maltreatment were associated with children’s heightened subjective stress responses, as indexed by the higher overall levels of negative emotion, which in turn led to elevated externalizing behavior. The indirect effects of parental physical maltreatment on externalizing behavior through heightened subjective stress response were also significant. In conclusion, findings of this dissertation highlight the role of the hypothalamic-pituitary-adrenal (HPA) axis and its hormonal end product, cortisol, in the relationship between the detrimental caregiving environment (e.g., parental physical maltreatment) and the development of externalizing problem behaviors in childhood. This notion has been supported by both findings of daily basal cortisol concentration (Study 2) and stress-induced HPA axis responses (Study 3). Also, this work provides preliminary evidence that the relationship between parental physical maltreatment and externalizing problem behavior might be explained by differences in emotional response to stress. A better understanding of individual differences in the adversity–psychopathology associations will require continued work addressing how multiple biological, emotional, and behavioral systems work in concert to shape development.