Can the 'love hormone' oxytocin keep men from cheating?

Oxytocin is often called the "love hormone" because of its unique ability to help couples bond on a deeper level. Lesser known is the hormone's rumored ability to keep partners from straying while in a monogamous relationship. To see if that is indeed the case, researchers at the University of Bonn in Germany set up an experiment to put committed men, not so different from Gen. David Petraeus and his now-public indiscretions, to the test. Here's what went down:

First things first: What is oxytocin?

It's a "powerful hormone" crucial to building feelings of attachment, says Psychology Today. "When we hug or kiss a loved one, oxytocin levels drive up." Levels of the hormone also increase dramatically during sex, birth, and breast feeding. According to Dr. René Hurlemann at Bonn University, previous research showed that oxytocin plays a key role in the "monogamous fidelity" of prairie voles. He and his team wanted to test if the same was true for human couples.

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How was the experiment conducted?

Hurlemann enlisted a group of 57 heterosexual men — some of whom were in relationships — and administered a nose spray containing either oxytocin or a placebo to each of them. They were then put in the same room with an attractive woman, who, as the experiment progressed, would stand at various distances from the subjects. Participants were asked to indicate whenever the woman was at an "ideal distance" or a distance that made them feel "slightly uncomfortable." In another phase of the experiment, the men were told to approach the woman, choosing how close they wanted to get. Hurlemann had a hunch that the men given oxytocin would feel more comfortable with the woman coming closer.

What happened?

"Surprisingly, the exact opposite happened," says George Dvorsky at io9. Men in committed relationships who were given the oxytocin, or as some call it, the "trust hormone," kept a greater physical distance from the woman than did single men. The betrothed men who inhaled oxytocin also insisted on more distance than did the committed men who took a placebo. This was true whether the experimenter maintained eye contact or averted their gaze and regardless of who was doing the approaching. Interestingly, the oxytocin did not affect the men's attitude toward the experimenter, who was rated "attractive" whether the subject was given the oxytocin or the placebo.

What does that mean?

When oxytocin is administered as a spray, says Hurlemann, "what we actually simulate is a kind of post-coital posture." The hormone presumably makes men in committed relationships think, why "approach another woman when you're in a post-coital situation? It doesn't make much sense." More importantly, this study shows that "one's relationship status affects how oxytocin affects the brain" and "provides some evidence that our brains evolved to form long-term romantic relationships," says Paul Zak, founding director of the Claremont Graduate University's Center for Neuroeconomics Studies, who wasn't involved in the study. Playboy magnate Hugh Hefner "is the exception, not the role model for men."

Sources: io9, LiveScience, The Los Angeles Times, Psychology Today, Telegraph