In the trust game participants played either the role of investor or trustee. Investors chose how much money to hand over to the trustee. The trustee, in turn, would then decide how much money to hand back after the financial stake quadrupled in size.
Investors who smelled a dose of oxytocin before playing the game were far more likely to hand over money than those in a control group who received a placebo.
Notably, the effect was not seen when the trustee was replaced with a computer. This suggests that oxytocin makes people more willing to engage in social interaction and not just more likely to take risks.
Oxytocin only increased trust, not the reliability of the trustee. "Trustee behavior is dominated by a principle of reciprocity, for which oxytocin seems irrelevant," Antonio Damasio, a neurology professor at the University of Iowa College of Medicine in Iowa City, writes in an accompanying article in Nature.
Scientists believe oxytocin could work as a kind of neurotransmitter in brain regions associated with emotional and social behaviors. A person's appraisal of a situation could trigger a chain of neural events, including the release of oxytocin.
"Particular social mechanisms and social cues that foster trust, like a smiling face of the other person, may perhaps lead to increases in oxytocin levels and therefore to higher probabilities of trust," said Kosfeld, the economist.
The findings may have direct clinical implications. Heinrichs, the psychologist, has been conducting several studies on the use of oxytocin in treating anxiety disorders, such as social phobia.
"In first analyses we see that a single dose of oxytocin enables patients with severe social phobia to reduce anxiety," Heinrichs said.
The role of oxytocin could also help scientists to better understand disorders that cause some people to display too much trust. Children with a rare genetic disorder known as Williams syndrome, for example, approach strangers indiscriminately. The children's high level of trust could be due to excessive oxytocin release, scientists speculate.
"This is the beginning of understanding human trust and positive social interaction from a biological point of view," Heinrichs said.
Of course, one could also imagine more dubious uses for the "trust potion"say, if car dealers or investment bankers sprayed their offices with oxytocin.
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