Oxytocin, vasopressin and trust: Associations with aggressive behavior in healthy young males

Oxytocin enhances trust during social interactions and reduces the tendency for social betrayal. Animal studies have revealed that oxytocin is also an important factor in the establishment and regulation of aggression, for which social interaction is a critical precondition. In humans, however, the effects of oxytocin appear more nuanced and influenced by social context and personality traits. Moreover, the pro-social effects of oxytocin are not mirrored by vasopressin, despite their high chemical similarity. Rather, vasopressin has been associated with an increase of aggressive responses. Therefore, we sought to investigate the association of oxytocin and vasopressin with trust and aggressive behavior. Overnight urinary oxytocin and vasopressin levels were obtained from 62 healthy males (age range: 18-26 years) to compare with trait measures of trust and aggressive behavior. We found a significant interaction of oxytocin and trust on aggression in which low trait measures of trust, in combination with low levels of oxytocin, were associated with a history of aggressive behavior. Notably, we found no significant associations for vasopressin. Although both oxytocin and vasopressin have been shown to be important in the emergence of violent behavior, our study suggests that oxytocin may be particularly modified by affiliative behaviors. These findings provide insights into the neuropsychological influences of oxytocin, and highlights the potential for clinical translation regarding the treatment of patients who exhibit recurrent aggressive behavior.