A study published Tuesday in the Journal of Neuroscience has uncovered a surprising new property of oxytocin, finding that when men in monogamous relationships got a sniff of the stuff, they subsequently put a little extra space between themselves and an attractive woman they'd just met.
Oxytocin didn't have the same effect on single heterosexual men, who comfortably parked themselves between 21 and 24 inches from the comely female stranger. The men who declared themselves in "stable, monogamous" relationships and got a dose of the hormone chose to stand, on average, about 6 1/2 inches farther away.
When researchers conducted the experiment with a placebo, they found no differences in the distance that attached and unattached men maintained from a woman they had just met.
Even when an attractive woman was portrayed only in a photograph, the monogamous men who received oxytocin put a bit more distance between themselves and her likeness. But when the new acquaintance was a man, administration of oxytocin did not prompt attached men to stand farther away than single men, the researchers reported.
The latest findings suggest that oxytocin, which floods the body in response to orgasm, early romance, breast-feeding and childbirth, may act more subtly in humans than has been widely understood.
A mounting body of recent research suggests that boosting oxytocin in the human brain will indiscriminately promote trusting, friendly behavior. Research on female prairie voles has suggested the chemical might play some role in pair-bonding, and in humans playing games of risk and power, it increased empathy and trust in males and females alike. Injected into the cerebrospinal fluid of male rats, oxytocin causes spontaneous erections.
Accordingly, researchers examining oxytocin's effects on people — including the authors of the latest study — assumed that men under its influence would draw closer to women, not farther away.
"This was quite surprising," said Dr. Rene Hurlemann, a psychiatrist at the University of Bonn in Germany, who led the study.
At the same time, the new findings make evolutionary sense, Hurlemann added: As human societies evolved to give men an increasing role in safeguarding and supporting their mates and offspring, it appears that oxytocin may have taken on a more discriminating role in human interaction by favoring staying over straying behavior among men who've already found a mate.
Paul Zak, founding director of Claremont Graduate University's Center for Neuroeconomics Studies, said the new findings squared nicely with research, including his own, suggesting oxytocin doesn't merely make people friendlier — it makes them more empathetic, more attuned to social cues, and more inclined to adjust their behavior accordingly.
But the study also suggests something important about the ways in which the human brain differs from those of other animals, said Zak, who was not involved in the German experiments.
"The finding that one's relationship status affects how oxytocin affects the brain provides some evidence that our brains evolved to form long-term romantic relationships," Zak said. "Hugh Hefner is the exception, not the role model for men."
Inhaled oxytocin was marketed until 1997 in the United States under the name Syntocinon as an aid to new mothers having difficulty with breast-feeding. (It was withdrawn for business reasons unrelated to safety concerns.) In recent years, it has been under investigation as a drug that may help those with autism or schizophrenia to strengthen social skills.
Oxytocin's effects in women are quite clear. It plays a pivotal role in childbirth (its infused synthetic form, called Pitocin, is used to induce labor) and in breast-feeding, where it facilitates the "letdown" of milk.
For men, however, the chemical's effects have been mysterious. High levels of testosterone, for instance, inhibit the release of oxytocin.
Asked whether an oxytocin nasal spray might be used to help philandering males resist temptation, Hurlemann chuckled and asked whether any drug could be so powerful. At the same time, he underscored that high levels of oxytocin — or its more masculine counterpart, the hormone vasopressin — are produced by the body in response to sexual activity, cuddling or even the touch or close physical presence of a mate.
"What we actually simulate is a kind of post-coital posture" with the nasal administration of oxytocin, Hurlemann said. "And why should you actually approach another women when you're in a post-coital situation? It doesn't make much sense."
For women whose partners seem to get a little too friendly with new female acquaintances at parties, he said, the effects of inhaled oxytocin might be achieved by other means.
"It might make a lot of sense to remind him of the relationship, and sexual activity might be one means of achieving this," Hurlemann said. "I'm not sure it's politically correct to say so, but from a biological point of view, it makes sense."
By Melissa Healy, Los Angeles Times, November 13, 2012, 6:27 p.m. Original article
Press Release from University of Bonn
Oxytocin Keeps Flirting Folks at Arm's Length
A team of researchers under the aegis of the University of Bonn tested the 'love hormone' on men
Flirting brings women and men closer. But the "social distance" ensures that they will keep a certain spatial distance from each other. Researchers under the leadership of the University of Bonn studied whether this distance can be diminished by the so-called love hormone, oxytocin. The exact opposite turned out to be true – men who were in a committed relationship even maintained a greater distance from an attractive woman when under the influence of oxytocin than their control group. The study has just been published in the renowned "Journal of Neuroscience."
When people approach each other, unconscious rules are at work. They will walk towards each other and will then talk while remaining at a very distinct distance, called "social distance" by scholars. "When they are approached beyond a certain distance, participants in a con-versation feel uncomfortable," said René Hurle¬mann, head of the research group that conducted the study at the Department of Psychiatry of the University of Bonn. A very sensitive case of social distance is the one between a woman and a man when flirting. "The magic of the initial encounter often decides what it will turn into," says Dr. Hurlemann.
Major releases of oxytocin during sex and at childbirth
Together with colleagues from the Universities of Bochum and Chengdu, his team studied the effect oxytocin, a neuro¬peptide, has on the social distance between women and men. "This neurotransmitter is often called the 'love hormone,' reports Professor Wolfgang Maier, Director of the Department of Psychiatry of the University of Bonn, who also performs research for the German research center of neurodegenerative diseases (DZNE). It has long been known that the release of oxytocin in the brain is particularly strong during sex, or in parents, after the birth of their child. "This hormone contributes to strong social attachment," adds Prof. Maier.
Researchers applied the hormone as a nasal spray
The researchers gave a total of 57 adult male subjects either oxytocin or a placebo in the form of a nasal spray. The experiment was conducted using an attractive female researcher as the experimenter. The subjects approached her and remained standing in front of her at a distance of about 60 centimeters. "We wanted to find out whether the social distance can be influenced by means of the hormone," report researchers Dirk Scheele and Dr. Nadine Striepens. They hypothesized that oxytocin would result in a diminished social distance in the subjects because this substance is reputed to promote social relationships. To their surprise, the exact opposite happened – the male test subjects who had received oxytocin as a nasal spray and were in a relationship with a woman kept a greater distance from the attractive female researcher than subjects who were single or came from the control group who did not receive the hormone.
Oxytocin acts as a kind of "fidelity hormone"
"Here, oxytocin acted as a kind of 'fidelity hormone,' Dr. Hurlemann sums up the results. Men with female partners increased the distance. Single men and control subjects who had not received oxytocin, however, were more exposed to the sexual attractiveness of the experimenter. An additional experiment yielded quite similar results. The researchers showed the subjects photos of attractive women. The test subjects had an option to zoom in on the images – i.e., to approach them more closely. When administered oxytocin, men in a relationship did this more slowly than single men.
The hormone increases the chances of survival
"This provided us with important insights into what makes men tick," Dr. Hurlemann sums it up. Oxytocin had a key role in Nature's mechanism for ensuring that both parents fully focus on their vulnerable offspring. "The fidelity hormone kept men from immediately turning to another woman, after impregnating the partner, which increased the chances of survival for human offspring in pre-civilization times."
Oxytocin Modulates Social Distance between Males and Females, The Journal of Neuroscience, DOI:10.1523/JNEUROSCI.2755-12.2012
René Hurlemann, MSc MD PhD
Attending psychiatrist and head of the Neuromodulation of Emotion (NEMO) Research Group
Department of Psychiatry of the University of Bonn
Ph: +49 228-28 71 50 57
From the study:
...While the most obvious physiological stimulus for promoting endogenous OXT [oxytocin] release in men would be having sex with their mate (Krüger et al., 2003), the simple close presence and touch of their partner at any given moment in time might also suffice (Holt-Lundstad et al., 2008). Thus OXT effects in promoting monogamy in males may normally depend upon the presence of a close positive relationship in the bond with their female partners and a close physical proximity between them.
Note: Sex may not, in fact, be as effective as touch because coitus with ejaculation leads to a rapid drop in oxytocin.