April 29, 2014
Rhesus Monkey Infants Express Sociability While On Oxytocin: Study
Brett Smith for redOrbit.com - Your Universe Online
Involved in child birth and the production of breast milk, oxytocin is a hormone produced in the pituitary gland. A new study published in the Proceedings of the National Academy of Sciences has found that this hormone also promotes social behavior in infant rhesus monkeys, or macaques.
While the hormone has been shown to promote a number of social behaviors in adults before, the recent study has shown this effect in primate infants of any species for the first time.
"It was important to test whether oxytocin would promote social behaviors in infants in the same respects as it appears to promote social interaction among adults," said study author Elizabeth A. Simpson, a genetics researcher currently at the NIH's Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD). "Our results indicate that oxytocin is a candidate for further studies on treating developmental disorders of social functioning."
Previous research has shown that oxytocin is important in parental bonding, mating, and also in social dynamics. Due to its role in social experiences, many scientists have indicated that oxytocin could be valuable as a remedy for disorders affecting social behaviors, such as autism spectrum disorders.
In the new study, the scientists started by evaluating the ability of rhesus macaques to replicate two facial gestures: lip smacking and sticking out the tongue. For lip smacking, the lips are extended and open, then smacked together over and over again – an activity that rhesus mothers will do with their infants in the first weeks after giving birth. Although tongue protrusion is seen in other primates and normally not observed in macaques, the animals will imitate it when their human caregivers show it, the study authors said.
By tracking the monkeys' capability to mimic the two gestures, the scientists sought to figure out if oxytocin could foster social interaction through a gesture that was normal to them and through a gesture not in their normal communication range.
The scientists tested the newborns in the first week after birth. Three times per day, every other day, the caregivers would display the facial gestures in a pattern to the newborn monkeys, while the animals' reactions were documented on video. At this phase of the study, the scientists discovered monkeys who gestured more often and referred to them as strong imitators.
In the second week, the scientists began testing the monkeys on two different days. The newborn monkeys breathed in an aerosolized dose of oxytocin in one session, and a saline placebo in the other. In every session, the dose was provided with an inhalation mask held softly over the animal's face.
In general, the primates were more social after receiving oxytocin, making facial gestures more often, than they were after getting the saline. The monkeys were more prone to participate in lip smacking than tongue extension, but were still more inclined to take part in either of these expressions after oxytocin than after the saline. There also were inconsistencies in the regularity of gesturing among the various monkeys, with the strong imitators transforming into even greater imitators after getting oxytocin.
After the oxytocin dose, the strong imitators were more prone to look at caregivers and stand near to them than they were after the saline. Examining a caregiver's face and staying close to a caregiver are indicators of social connection and social interest, Simpson said.
In a different test, the scientists discovered that oxytocin caused the monkeys to have reduced levels of the stress hormone cortisol in their saliva – an indication that oxytocin may also diminish anxiety, the scientists concluded.