Oxytocin, a hormone associated with trust and social bonding, also helps people recognize familiar human faces, according to a new study. Researchers say the findings, published today in The Journal of Neuroscience, could shed light on the causes of mysterious neurological and psychological disorders.

"There is initial evidence that the central oxytocin system is altered in several mental disorders that are characterized by severe social disturbances, such as autism spectrum disorders, obsessive-compulsive disorder, [and] personality disorders," says lead study author Ulrike Rimmele, a psychologist at the University of Zurich in Switzerland. "Knowing how oxytocin affects basic social mechanisms, such as recognition of another human being, is an essential pre-requisite to the study of more complex human behavior."

Oxytocin is produced in the hypothalamus (a brain structure that controls hunger and moods) and affects  several brain regions including the amygdala and the fusiform gyrus, which are believed to help us recognize faces. In response to certain stimuli, the pituitary gland, located at the base of the brain, secretes oxytocin (among other hormones) into the bloodstream. The hormone is known to trigger uterine contractions during pregnancy and  the release of milk from breast ducts during nursing; studies also suggest  that it may promote bonding between new moms and babies.

Oxytocin levels increase during sex and peak at orgasm, leading scientists to suspect that it plays a key role in forming emotional attachments.

Rimmele's team split 41 healthy men into two groups, one of which was given a nasal spray containing oxytocin and the other a nasal spray without it. About an hour later—enough time for the oxytocin to take effect in the brain—the men were shown a series of 168 images, half of human faces and half of nonliving things such as houses and landscapes.

The next day, the men were shown the exact same pictures, along with 72 new ones. When asked to identify the images they had previously seen, members of the oxytocin group had a 46 percent recognition accuracy compared with 36 percent accuracy among the placebo crowd.

"This [study] tells us the mechanism by which we allow people to get close to us—we know who they are," says Paul Zak, an economist who directs the Center for Neuroeconomic Studies at Claremont Graduate University in California. "Recognizing people around us is not a trivial task. It essentially tells us why we have civilization."

Image credit ©iStockphoto.com/Joan Vicent Cantó Roig