Abstract:

Psychological resilience refers to the process of effective and flexible adaptation in the face of adversity, trauma, tragedy, threats, and other significant sources of stress. It helps the organism restore to a normal physiological and psychological status. Psychological resilience plays a major mediating role in the development of post-traumatic mental illness in individuals. It can predict the negative emotions after stress and determine the adaptation to stress. It has a significant influence on physical and mental health. Previous studies have shown that the hippocampus plays an important role in psychological resilience, and oxytocin may promote psychological resilience by modulating the hippocampus. However, the specific regulation mechanisms of them have not yet been systematically researched and elucidated. This review focuses on the role of oxytocin in the hippocampus on regulating psychological resilience and try to clarify the underlying mechanisms. It can help to further understand the mechanisms of psychological resilience and help to reduce the incidence of post-traumatic mental illness.
Hippocampus regulates psychological resilience through the internal and external projection circuits. On the internal circuit of the hippocampus, studies suggest that “entorhinal cortex-dentate gyrus-CA3” circus in the hippocampus may improve psychological resilience by reducing the generalization or promoting the extinction of stress-related memory. On the external circuit of the hippocampus, the “dentate gyrus-amygdala-nucleus accumbens” circuit and the “hippocampus-nucleus accumbens” circuit may enhance or reduce psychological resilience by promoting reward and disgust, respectively. There is a opposite effect on psychological resilience from the projection of the hippocampus to nucleus accumbens directly or indirectly. The basolateral amygdala may play a key role. Studies have shown that stress can cause complex interactions among basolateral amygdala, hippocampus and nucleus accumbens, so more research is necessary conducted to better understand its specific mechanisms. 
Oxytocin may regulate the hippocampus through four ways to improve psychological resilience. First, oxytocin promotes the neurogenesis of the hippocampus under stress by acting on the oxytocin receptor at the hippocampal CA3 pyramidal neurons. This can reduce the stress-induced harm. Second, oxytocin reduces the sensitivity of mature neurons in ventral hippocampus to stress by stimulating dentate gyrus neurogenesis. This can enhance the function of “pattern separation” in the dentate gyrus–CA3 circuit and reduce the generalization of stress-associated memory. Third, oxytocin increases the synaptic cell signaling pathway kinase levels on the CA3-CA1 pathway and promotes the ability of adaptation to stress by rescuing stress-induced impairments in NMDA receptor-dependent long-term potentiation of hippocampal Schaffer collateral-CA1 synapses. At last, oxytocin interacts with glucocorticoids and catecholamine systems to increase oxytocin release. The oxytocin release can inhibit the function of the hypothalamic–pituitary–adrenal axis and reduce hippocampal glucocorticoid receptor levels. This protects the structure and function of the hippocampus from glucocorticoid damage and re-establishes brain homeostasis. So, oxytocin can further adjust the stress-related memory and enhance psychological resilience.
At the same time, research suggests that oxytocin regulates psychological resilience by affecting the structure and function of the hippocampus, which might differ among individuals of different genders or experiences. In terms of individual diagnosis and treatment, it is necessary to combine these factors for reasonable treatment. Besides, the interaction between genes and the environment is also needed to be considered. To improve psychological resilience in a targeted manner, individual characteristics, interpersonal relationships, and emotional support needs to be considered in the treatment of stress-related mental illness. Finally, exploring the neural mechanisms of psychological resilience should be closely integrated with human research and animal research to make up for the deficiencies of each research. Future research should combine various technologies such as human brain imaging and animal neural circuits technologies to determine the fine brain structures and circuits that regulate psychological resilience.

Key words: psychological resilience, stress, stress adaptation, oxytocin, hippocampus