MONDAY, July 7 (HealthDay News) -- Science may have confirmed what most moms already know: When a woman sees her baby smile, certain areas of her brain activate, stimulating happy feelings.

"There's a definite biological origin to these feelings that mothers have," said study author Dr. Lane Strathearn, an assistant professor in the department of pediatrics at Baylor College of Medicine in Houston. "The contrast that showed the most response in the dopaminergic system of the brain was when a mother's own baby smiled compared to an unknown baby face."

"A baby's smile is a very powerful stimulus," noted Strathearn. "It makes sense biologically. Babies are completely and utterly dependent on their caregivers. It makes sense that nature would build in a system that would reinforce that relationship."

A woman's crying infant, or even her baby with a neutral expression, doesn't evoke the same type of brain response as occurs when her baby is smiling, the study found.

Strathearn said they haven't had a chance to look at the effects on fathers. His team published its findings in the July issue of Pediatrics.

For the study, the researchers recruited 28 first-time mothers during their last trimester of pregnancy. At that time, Strathearn said the women completed "attachment interviews" to assess the types of experiences they had when being raised and what type of relationship these mothers had with their own parents.

The average age of the women was 29, and most had at least a college degree. Thirteen of the women were white, seven were black, four were Hispanic, and four listed their race as other. Most of the women -- 20 -- were married.

Then the researchers met with the mothers and the babies when the babies were about 6 months old. At that time, they videotaped them and captured smiling, crying and neutral pictures of the babies. When the babies were about 10 months old, they asked the mothers to come back in for a functional MRI (fMRI) scan that shows which areas of the brain are activated.

When the mother's saw photos of their own baby's face, an extensive brain network was activated, according to the study. But, it was when mothers saw their own infant's happy face that the dopaminergic reward system in particular was activated. This system was not activated when mothers saw their own children looking either sad or neutral.

"This study is fascinating. It's a step towards unraveling the chemistry of emotion, and it begins to show the complex chemistry of the mother-child relationship," said Dr. Michael Wasserman, a pediatrician at Ochsner Health System in New Orleans.

Strathearn explained that for some mothers, there may be a problem in this natural reward system, and that may help to explain why some women never bond with their children or even abuse their children.

More information

The Nemours Foundation has more on bonding with your baby.

SOURCES: Lane Strathearn, M.B.B.S., assistant professor, pediatrics, Baylor College of Medicine, Houston; Michael Wasserman, M.D., pediatrician, Ochsner Health System, New Orleans; July 2008 Pediatrics

Last Updated: July 07, 2008

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