A hug from Mom can help soothe a stressed child, but new research shows that just hearing her voice can initiate the same biochemical responses—even if the mother is speaking over the phone.

The hormone oxytocin promotes bonding between mother and child and has long been associated with close physical contact (often through early-infant skin-to-skin interaction such as breastfeeding and soothing).

"It was understood that oxytocin release in the context of social bonding usually required physical contact," Leslie Seltzer, a post-doctoral fellow at the University of Wisconsin-Madison's Child Emotion Lab and lead author on the study, said in a prepared statement. "But it's clear from these results that a mother's voice can have the same effect as a hug, even if they're not standing there."

For the experiment, Seltzer and her colleagues had 61 seven- to 12-year-old girls perform math and public-speaking tasks in front of an audience of strangers. (These are frequently employed stress tests for children.) Afterward, 19 girls were turned back over to their mothers, who gave comfort for 15 minutes, in part through reassuring physical contact with the girls. Alternatively, 20 of the girls received a 15-minute-long call from their mothers on a phone provided by the researchers. The remaining 22 girls watched an emotionally neutral movie for 75 minutes. (The two other groups also were shown 60 minutes of the same neutral movie after their 15 minutes of maternal contact.) To test levels of the stress hormone cortisol, samples of spit were collected seven times over the course of the experiment, and levels of oxytocin were monitored through four urine samples that were collected.

The researchers found that "the children who got to interact with their mothers had virtually the same hormonal response, whether they interacted in person or over the phone," Seltzer said. The results were published online May 11 in the journal Proceedings of the Royal Society B.

By the end of the experiment, those girls who had spoken with their mothers over the phone had about the same levels of cortisol as those who had met with their mothers in person (though the phone group's levels took longer to arrive at that lower amount). Both of these groups had much less cortisol in their saliva than those who had had no contact with their mothers after the stressful endeavor.

The effect of talking to Mom was even more dramatic when assessed via subjects' levels of oxytocin. "Girls released conspicuously similar levels" of the bonding hormone whether they had spoken with their mothers or had physical contact with them by the end of the session, Seltzer and her team found. (The girls who did not have contact with their mothers after the stress event had consistent, lower levels of oxytocin.)

"That a simple telephone call could have this physiological effect on oxytocin is really exciting," Seth Pollak, director of the lab, said in a prepared statement.

"For years I've seen students leaving exams and the first thing they do is pull out their cell phone and make a call," Pollak said. "I used to think, 'How could those over-attentive, helicopter parents encourage that?' But now? Maybe it's a quick and dirty way to feel better. It's not pop psychology or psychobabble."

The researchers are now wondering if other species have the same hormonal response. "Lots of very social species vocalize," Seltzer said, noting that findings across the animal kingdom could shed light on "questions of social behavior and evolutionary biology."

But in the meantime she's exploring the impact of other forms of communication on hormone levels. Could a text from Mom help calm the nerves as well?

Image courtesy of iStockphoto/sjharmon