Oxytocin
Nasally administered oxytocin has been reported to reduce fear, possibly by inhibiting the amygdala (which is thought to be responsible for fear responses). Indeed, studies in rodents have shown oxytocin can efficiently inhibit fear responses by activating an inhibitory circuit within the amygdala. Some researchers have argued oxytocin has a general enhancing effect on all social emotions, since intranasal administration of oxytocin also increases envy and "Schadenfreude". Individuals who receive an intranasal dose of oxytocin identify facial expressions of disgust more quickly than individuals who do not receive oxytocin. Facial expressions of disgust are evolutionarily linked to the idea of contagion. Thus, oxytocin increases the salience of cues that imply contamination, which leads to a faster response because these cues are especially relevant for survival. In another study, after administration of oxytocin, individuals displayed an enhanced ability to recognize expressions of fear compared to the individuals who received the placebo. Oxytocin modulates fear responses by enhancing the maintenance of social memories. Rats that are genetically modified to have a surplus of oxytocin receptors display a greater fear response to a previously conditioned stressor. Oxytocin enhances the aversive social memory, leading the rat to display a greater fear response when the aversive stimulus is encountered again.
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.