Oxytocin (OXT) is traditionally viewed as a female hormone that is primarily associated with labor and it has a very special affect on mothering. In mothers it increases their attachment to their infant, promoting the feeling of love, and makes her infant more valuable to her. Oxytocin has been called the love and bonding hormone. Furthermore, oxytocin mediates attachment behavior over the course of development, with lower urinary concentrations of oxytocin found in maltreated children and in adult males with a history of early separation. Psychologically, oxytocin promotes a feeling of well being and tranquility. It also suppresses the fear that would normally cause a mother to back off from a threat. In humans, based on the animal literature, it has been postulated that beyond these peripheral actions, central OXT modulates cognition in the context of social interactions, thus promoting positive sociality.
In particular, recent experiments have shown that OXT promotes trusting behavior, enhances facial emotion recognition and memory for positive social information, reduces social stress, improves social cognition in socially impaired individuals with autism, and alters dysfunctional cognition in social phobia.
Functional imaging studies have just begun to elucidate the underlying neural correlates of these pro-social effects. A number of studies have provided evidence that the amygdala might be a key structure for the mediation of the social cognitive effects of OXT. Several studies have shown that a single dose of OXT reduced amygdala reactivity to pictures of aversive scenes and faces with negative valence.
While studies of oxytocin and monogamous behavior in humans have not been conducted to date, one study found that in co-habiting couples, greater partner support is associated with higher plasma oxytocin in both men and women before and after a period of warm partner contact.
The OXT system is a sexual dimorphic system. For example, OXT plasma levels tend to be higher in females and synthesis, as well as OXT receptor affinity, appears to be modulated by gonadal steroids such as estradiol and progesterone. It has been shown, in a study on prairie voles, that female parenting behavior is more dependent on OXT, whereas male parenting behavior is associated with vasopressin. Another study demonstrated that aggression is associated with OXT in females, but not in males. However, the hypothesis of homology between paternal and maternal behavior has not yet been adequately tested and it is possible that different neuroendocrine circuits could lead to the same behavior in males and females. Future studies should include both sexes to determine a possible sexual dimorphism in the neural effects of OXT, considering gonadal steroids and OXT receptor affinity.