"Trust" Hormone's Smell Helps Us Hand Over Cash, Study Says

Stefan Lovgren
for National Geographic News
June 1, 2005
When large sums of money are concerned, it is advisable to trust nobody, mystery writer Agatha Christie once said.

But what if there is a biological reason for why we would trust others with our cash?

Scientists have discovered that the hormone oxytocin, when sniffed, makes people more prone to trust others to look after their money.

To test the trusting effect of oxytocin, the researchers studied people who played an investment game. In the game, participants would choose how much money to hand over to a trustee. Investors were far more trusting after inhaling the hormone, researchers found.

"This is the first study that can describe the underlying biological mechanism of trust in humans," said Markus Heinrichs, a clinical psychologist at the University of Zurich in Switzerland. Heinrichs co-authored the study, which will appear tomorrow in the journal Nature.

The findings have important implications for the study of conditions in which trust is diminished (as in the mental disorder autism) or augmented. Ongoing research suggests that inhaling oxytocin may help reduce anxiety in people with social phobia, for example, and help them to interact better with others.

Animal Bonding

Almost all human interactions—from love and friendship to leadership and economic transactions—require an element of trust. Yet little is known about the biological underpinnings of the feeling.

"We know a lot about institutional factors that foster trust—information, repeated interaction, and so on—but nothing about why we trust when there is basically no objective reason to do so," said Michael Kosfeld, an economist at the University of Zurich. Kosfeld is a co-author of the study.

That oxytocin would promote trust is not entirely surprising. Humans release the hormone during everything from labor to sexual orgasm. But in many animals the molecule is also known to promote social interactions, including pair bonding.

"I've been doing research on oxytocin in humans for many years and found positive effects of [it] on stress and anxiety," said Heinrichs, the psychologist. "However, I was not sure to find oxytocin to influence such a complex behavior like trust."

In animals oxytocin may lower the natural resistance they have to the proximity of others, making them more likely to approach other animals. Approach behavior and trust are closely linked.

Investing Cash

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.

Reducing Anxiety

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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