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.
Marinus van IJzendoorn
In humans, oxytocin has been shown to be associated with delivery, mood regulation, sexual functioning and parenting behaviours. Emerging studies are showing an increasing link between oxytocin levels in humans and parent-child relationships. One idea is that increased oxytocin levels facilitates postnatal parental behaviour and the formation of an emotional bond between parent and infant, in mothers and fathers alike, by acting to reduce anxiety and ameliorate responses to external stresses. Parents who have a less anxious state of mind are able to increase their focus on infant care, improve mood, and facilitate the capacity to read non-verbal infant cues and stimulate the social learning and reward system in response to infant cues. Although there are strong animal models for the role of oxytocin in parental behaviour, one of the key questions in the development of a psychobiology of human care-giving and attachment is the degree to which the considerable variation in parenting can be accounted for through similar biological mechanisms such as the moderating role of the oxytocin receptor gene (OXTR) polymorphisms and experimentally induced oxytocin levels.
Van IJzendoorn and colleagues conducted several correlational studies documenting the role of OXTR in parenting, and carried out various randomized control trials showing that oxytocin enhances male and female sensitivity to child signals, in natural play settings as well as with a cry test, using behavioural assessments, EEG/ERP, and fMRI. A meta-analysis of experimental studies with intranasal oxytocin administration was conducted showing that feelings of trust are elevated and that the expected lowering of out-group trust was not confirmed.