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.
Social connection
In mammals, oxytocin has been found to be released during childbirth, breastfeeding, sexual stimulation, bonding, and in some cases stress. In 1992, Sue Carter discovered that administering oxytocin to prairie voles would accelerate their monogamous pair-bonding behavior. Oxytocin has also been found to play many roles in the bonding between mother and child. In addition to pair-bonding and motherhood, oxytocin has been found to play a role in prosocial behavior and bonding in humans. Nicknamed the “love drug” or “cuddle chemical,” plasma levels of oxytocin increase following physical affection, and are linked to more trusting and generous social behavior, positively biased social memory, attraction, and anxiety and hormonal responses. Further supporting a nuanced role in adult human bonding, greater circulating oxytocin over a 24-hour period was associated with greater love and perceptions of partner responsiveness and gratitude, however was also linked to perceptions of a relationship being vulnerable and in danger. Thus oxytocin may play a flexible role in relationship maintenance, supporting both the feelings that bring us closer and the distress and instinct to fight for an intimate bond in peril.