A baby's smile gives mothers a natural high

Scientists say the baby's smile that brightens a mother day also lights up a part of her brain.

The researchers from the Baylor College of Medicine (BCM), Houston, Texas, say a baby's smile lights up the reward centers of the mother's brain and an extensive brain network seems to be activated.

The researchers say the finding could help scientists understand the special mother-infant bond and how it sometimes go wrong.

Dr. Lane Strathearn, assistant professor of pediatrics at BCM and Texas Children's Hospital and a research associate in BCM's Human Neuroimaging Laboratory, says the relationship between mothers and infants is critical for child development and sometimes that relationship doesn't develop normally and this can result in neglect and abuse with devastating effects on a child's development.

In order to study this relationship, Strathearn and his colleagues asked 28 first-time mothers with infants aged 5 to 10 months to watch photos of their own babies and other infants while they were in a functional magnetic resonance imaging scanner.

This is a machine which measures blood flow in the brain and the scans pick up areas of increased blood flow which "light up," giving researchers a clue as to where brain activity is taking place.

Some of the photos showed the babies smiling or happy but in others they were sad, and in some they had neutral expressions.

The researchers found that when the mothers saw their own infants' faces, key areas of the brain associated with reward lit up during the scans....the areas stimulated were those associated with the neurotransmitter dopamine.

The specific areas associated included the ventral tegmental area/substantia nigra regions, the striatum and frontal lobe regions involved in emotion processing, cognition and motor/behavioural outputs.

Dr. Strathearn says the strength of the reaction depended on the baby's facial expression and the same areas have been activated in other experiments associated with drug addiction. He says maybe seeing their own baby's smiling face produced a 'natural high'.

Dr. Strathearn says the strongest activation was with smiling faces and there was less effect from pictures of their babies with sad or neutral expressions.

The researchers were expecting a different reaction to the sad faces but they found little difference in the reaction of the mothers' brains to their own babies' crying face compared to that of an unknown child.

Overall, the mothers responded much more strongly to their own infants' faces than to those of an unknown baby and Dr. Strathearn says understanding how a mother responds uniquely to her own infant, when smiling or crying, may be the first step in understanding the neural basis of mother-infant attachment.

Also involved in the study were UK researchers from University College London.

The research was funded by the National Institutes of Health, the Kane Family Foundation, the National Institute of Neurological Disorders and Stroke and the National Institute on Drug Abuse.