Oxytocin is associated with human trustworthiness.

Human beings exhibit substantial interpersonal trust-even with strangers. The neuroactive hormone oxytocin facilitates social recognition in animals, and we examine if oxytocin is related to trustworthiness between humans. This paper reports the results of an experiment to test this hypothesis, where trust and trustworthiness are measured using the sequential anonymous "trust game" with monetary payoffs. We find that oxytocin levels are higher in subjects who receive a monetary transfer that reflects an intention of trust relative to an unintentional monetary transfer of the same amount. In addition, higher oxytocin levels are associated with trustworthy behavior (the reciprocation of trust). Absent intentionality, both the oxytocin and behavioral responses are extinguished. We conclude that perceptions of intentions of trust affect levels of circulating oxytocin.

The neurobiology of trust.

This is the first report that endogenous oxytocin in humans is related to social behaviors, which is consistent with a large animal literature. Subjects are put into a social dilemma in which absent communication, cooperative behavior can benefit both parties randomly assigned to a dyad. The dilemma arises because one participant must make a monetary sacrifice to signal the degree of trust in the other before the other's behavioral response is known. We show that receipt of a signal of trust is associated with a higher level of peripheral oxytocin than that in subjects receiving a random monetary transfer of the same average amount. Oxytocin levels were also related to trustworthy behavior (sharing a greater proportion of the monetary gains). We conclude that oxytocin may be part of the human physiology that motivates cooperation.