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    早期应激经历往往会提高个体患病的风险和几率，其背后的机制是当前研究的前言和热点。在己有的研究中，主要从生理和心理功能两个方面来考量。其中，从生理的神经内分泌层面来说，下丘脑一垂体一肾上腺皮质轴(HPA轴)是个体应对应激时的主要响应机制，如果个体长期处于应激状态，HPA轴会被反复激活，从而改变其响应的程度。从心理功能的角度来看，前额叶是应激作用的主要靶脑区，而早期应激发生的时间刚好处于前额叶发育成熟的关键时期，考虑到前额叶在执行功能中扮演的重要角色，早期应激还可能导致前额叶相关的执行功能的改变，甚至对执行功能产生深远的影响。
    在以往的研究中，早期应激对HPA轴影响存在不一致结果，而且被试样本多包含临床样本，因此结果不一致可能是受到了当前疾患的影响。同时早期应激对执行功能的研究多集中在行为层面，有极少量的核磁研究，脑电研究几乎没有。因此，本论文将继续从这两方面开展研究，首先从神经内分泌层面上考察早期应激对于成年期HPA轴反应性(用其最终产物皮质醇为指标来衡量)的长期影响;其次，从行为和神经机制两个层面探讨早期应激对执行功能主要成分产生的长期影响。在本论文中，我们针对健康大学生/研究生被试群体进行了研究。在早期应激对皮质醇反应性的影响研究中，我们通过应激诱发范式成功诱发了心理应激，并在此过程中采集唾液皮质醇随时间变化的数据。在早期应激对执行功能影响的研究中，采用经典的持续性注意任务和N-back任务来分别测量抑制控制和工作记忆，采集并分析任务过程中的行为和脑电数据。除了关注任务中行为数据一一正确率、反应时等，我们关注了相关的脑电成分。在持续性注意任务中，主要关注了Nog。试次中的N2成分和P3成分，这两者和冲突检测、行为抑制过程相关。在N-back范式中，主要关注了P2成分和P3成分，这两者分别和早期注意分配、匹配等神经加工过程相关。本研究成果从不同层面说明早期应激对身心造成长期影响的机制，对应激相关疾病的预防和治疗有一定的启发意义。主要研究结果如下:
    (1)早期应激与心理应激任务下皮质醇反应负相关，即早期应激越严重，皮质醇升高越小。结合文献，我们认为这种降低的皮质醇变化反映了一种适应性的机制即早期应激者HPA轴反应性降低，从而避免了长期皮质醇过量可能带来的问题，有利于机体维持自身的内稳态。
    (2)在早期应激对冲突监控和抑制控制影响的研究中，我们未发现行为数据上的显著相关。但脑电数据显示，与冲突检a)n(相关的Nogo-N2的波幅随着早期应激程度的增大而减小，但与行为抑制和结果评估相关的P3波幅与早期应激相关不显著。这可能反映了在冲突监控过程中，早期应激的被试分配了相对较少的加工资源，冲突检测能力所下降。
    (3)在早期应激对工作记忆影响的研究中，我们发现早期应激和P3成分的潜伏期显著正相关。这可能反映了早期应激个体工作记忆中的匹配神经加工速度更慢，需要更长的时间来进行信息提取并与当前刺激进行比对。

    Previous studies showed that early life stress (ELS) is a risky factor causing physical and mental diseases. However, the underlying mechanism between ELS and many diseases were not very clear. After reviewing related literatures, we found two perspectives to see this problem. On the neuroendocrine level, the hypothalamic-pituitary-adrenal axis (the HPA axis) is an important stress response system. And the chronic or repeated exposure to stress during early life may cause the dysfunction of the HPA axis. On the other hand, the executive functions might be prone to be influenced by the ELS. Executive functions are depend on the frontal cortex which is the target area of cortisol (the end-product of the HPA axis). Besides, the frontal cortex is under an essential developing stage during childhood and adolescence.
    Considering the effect of the ELS on cortisol reactivity were inconsistent which might due to the current disorders. And the exploration of how the ELS affect the executive functions was mainly focusing on the behavioral level. Therefore, we tried to continue the exploration of the effect of the ELS on two aspects一HPA axis reactivity and executive functions.
    In the first part, Stress response was induced by a laboratory psychosocial stressor and the HPA axis reactivity was measured by salivary cortisol. In the second part, the executive functions were measure by the continuous performance test (CPT, mainly measuring inhibitory control) and N-back test (measuring working memory) on both behavioral level and neural level. On the neural level, we focused on the N2 component and P3 component of   Nogo trials' in CPT, they were associated with conflict monitoring and behavioral inhibitory process. In the N-back task, we paid attention to the P2 and P3 component, they were separately associated with attention distribution and matching process. The main results were fisted below:
    (1)ELS was negatively correlated with the cortisol reactivity to psychosocial stressor, which demonstrated that severe ELS was related to blunted cortisol reactivity. We suppose this is a sign of adaption to the early life adversities. And the blunted cortisol reactivity helped to avoid the toxic effect on our body and keep homeostasis.
    (2) In the CPT test, we found no significant correlation of ELS and behavioral indexes. However, the ERP results exhibited that ELS was related to lower Nogo-N2 amplitude. This might demonstrated the less resources was allocated in the conflict monitoring process.
    (3)In the N-back test, we found significant correlation between ELS and latency of P3 component, which might represent longer processing time before matching process of N-back task in the ELS individuals. They may need more time to extract related information and processing the new stimulus.