Oxytocin
It has been shown that oxytocin differentially affects males and females. Females who are administered oxytocin are overall faster in responding to socially relevant stimuli than males who received oxytocin. Additionally, after the administration of oxytocin, females show increased amygdala activity in response to threatening scenes; however, males do not show increased amygdala activation. This phenomenon can be explained by looking at the role of gonadal hormones, specifically estrogen, which modulate the enhanced threat processing seen in females. Estrogen has been shown to stimulate the release of oxytocin from the hypothalamus and promote receptor binding in the amygdala.
Human bonding
There is evidence in a variety of species that the hormones oxytocin and vasopressin are involved in the bonding process, and in other forms of prosocial and reproductive behavior. Both chemicals facilitate pair bonding and maternal behavior in experiments on laboratory animals. In humans, there is evidence that oxytocin and vasopressin are released during labor and breastfeeding, and that these events are associated with maternal bonding. According to one model, social isolation leads to stress, which is associated with activity in the hypothalamic-pituitary-adrenal axis and the release of cortisol. Positive social interaction is associated with increased oxytocin. This leads to bonding, which is also associated with higher levels of oxytocin and vasopressin, and reduced stress and stress-related hormones.