Abstract:

Disgust, as an important basic emotion, is commonly recognized as a toxin (pathogens) avoidance mechanism to protect individuals from diseases, and has far-reaching evolutionary implications and specific physiological mechanisms. Hormones are chemical messengers synthesized and secreted by endocrine cells, which affect the physiological activities of individuals by regulating the metabolism of various tissue cells. A large number of studies have found that the generation and expression of disgust involve many different hormones, including oxytocin, progesterone, estrogens, testosterone, corticosteroids, arginine-vasopressin, etc. These various systems of neuroendocrine regulations make individuals rapidly evaluate and integrate the information related to toxins and pathogen cues, and thus producing appropriate disgust and avoidance behaviors. In the current researches, oxytocin, progesterone and estrogens are the most widely studied hormones in the field of disgust. Based on animal and human researches, this article reviews and summarizes some evidence that the three hormones affect the processing of disgust and their neurophysiological mechanism and predicts future research direction.
Oxytocin is synthesized in the hypothalamus and is widely involved in social cognition and social behaviors, such as attachment. Studies have proved that oxytocin affects the generation and acquisition of disgust based on olfaction and taste, and recognition of disgust expression by regulating the activities of several brain regions such as insula, anterior cingulate gyrus, amygdala, piriform cortex, putamen, and middle frontal gyrus. Among them, oxytocin may participate in disgust learning by modulating the activity of serotonin receptors.
According to the compensatory prophylaxis hypothesis supported by quantities of animal and human researches, progesterone promotes the individuals’ sensitivity of disgust to potentially infectious stimuli, thereby producing avoidance behaviors to reduce the risk of infection. At the same time, progesterone also affects the recognition of disgust expressions, but has no significant effect on the disgust learning of rodents. And amygdala activity is the main brain area affecting the processing of disgust and can be both promoted and inhibited by progesterone in the processing of disgust. Estrogens also play regulatory roles in perception and acquisition of disgust and recognition of facial expression of disgust. The amygdala and the anterior cingulate gyrus may also be the neural substrates that progesterone affects the processing of disgust, but further research will be necessary before we can draw firm conclusions.
It is noteworthy that oxytocin, progesterone and estrogens affect the generation and expression of pathogen disgust to varying degrees, except for moral disgust. This may be because pathogen disgust is more closely related to hormones than moral disgust which has a higher cognitive component, and its physiological basis is more evident in evolution. However, this may be due to current questionnaires used to measure moral disgust making the measurement indicators insensitive enough, which causes no significant effects of the three hormones on moral disgust.
In short, most of the current studies in this field are still confined to describe phenomena and doing correlational research, but know little about its internal mechanisms. Besides, there are still many contradictions in results. Future studies should explore the effects of these hormones on disgust in different sensory channels and consider their moderating roles in different genders by accurately measuring hormone levels and controlling the task difficulties. In addition, researchers can combine neuroimaging technologies with behavioral studies to clarify the neuroendocrine mechanism of these hormones affecting disgust processing.

Key words: disgust, oxytocin, progesterone, estrogen, neurophysiological mechanism