Abstract: Fear recognition plays an important role in human survival and social adaptation. But the recognition accuracy of fear is often the lowest among the six basic emotions, especially in some patients with mood disorders. Oxytocin, a "love" and "attachment" hormone, has been widely used in recent years as a social-emotional cognitive therapy for autism patients. Oxytocin was found to bind to oxytocin receptors in the central amygdala to inhibit fear responses. However, oxytocin can also interact with the HPA axis (Hypothalamus - Pituitary - Adrenal axis), and enhance fear processing under stress. Consistently, intranasal oxytocin application reduced the accuracy and speed of fear recognition by inhibiting amygdala activation. However, some other studies with fear-recognition found that, intranasal oxytocin application enhanced amygdala responses and improved the accuracy of recognition, thereby promoted emotional understanding. These two-way effects were found in both healthy subjects and patients. The mechanism behind them may be related to the interaction between the oxytocin system with the HPA axis, both regulating fear-related behaviors in complex ways. Normally, oxytocin inhibits the medial output of the central amygdala, weakens the activity of the HPA axis, and reduces the secretion of stress hormones (cortisol, etc.) and fear recognition. However, under strong stress, the release of high concentration of oxytocin led to down-regulation of the receptors and the enhancement of HPA axis, and thus to improvement of the recognition of fear emotions. In human studies, the dose and time of oxytocin administration also affect this bidirectional mechanism. In addition, individual differences in the endogenous oxytocin system, such as experiences of early life stress, personality traits, and gender, may also influence the effects of the effects of oxytocin. In all, we can make these conclusions. First, different doses of exogenous oxytocin have different effects. High dose can improve the ability of fear recognition, whereas low dose can reduce the speed and accuracy of fear recognition. Second, the effects of oxytocin follow an "inverted U-shaped" curve after intranasal administration, peaking at about 45 minutes. Third, baseline levels of endogenous oxytocin vary significantly between individuals, and the efficacy of intranasal oxytocin application can be more easily observed by increasing oxytocin doses in attention-deficit individuals with lower baseline levels. In conclusion, there are complex combined mechanisms between exogenous and endogenous oxytocin systems. In the future, we need to pay more attention to the following aspects. First, it is better to combine eye movement with event-related potential technology, and to put more attention on regulation of oxytocin on fear recognition with different emotional cues. Second, facial perception involves multiple brain regions, but the exact mechanism by which oxytocin induces changes in amygdala functional connectivity is unclear and needs further exploration. Third, The HPA axis plays a complex role in the regulation and treatment of mood, social and behavior, but its interaction with oxytocin has been poorly studied. Finally, the individual differences of the subjects should be considered in the experiment, the changes of oxytocin levels before and after the experiment should be tracked, and the interaction between endogenous system and exogenous oxytocin drug therapy should be further studied by using biogenetic techniques.

Key words: fear recognition, amygdala, oxytocin, bidirectional effects

摘要： 恐惧情绪识别对人类社会生存与适应具有重要意义,催产素（oxytocin）已被证实既可以提高表情识别,也能抑制其加工。催产素是一种爱和依恋的激素,通过与中央杏仁核催产素受体结合抑制恐惧反应。但是,在应激状态下催产素也可以与HPA轴发生相互作用,从而增强恐惧情绪加工。此外,研究发现,催产素剂量、时间、内源水平差异都会影响其双向作用。未来需要跟踪实验前后体内催产素水平的变化,对实验给药与内源系统之间的相互作用进一步研究,为产后抑郁症等情绪疾病治疗提供理论依据。

关键词: 恐惧情绪识别, 催产素, 杏仁核, 双向作用