Tears and smiles bond secure mothers to baby

The sight of her baby's smile or even its tears cause the reward centres in a mother's brain to light up, according to an international functional magnetic resonance imaging (fMRI) study. However, they shine brightest only if the mother herself had a secure attachment to her own parent.

According to Lane Strathearn, lead author of the current research paper and an assistant professor of paediatrics at Baylor College of Medicine and the Texas Children's Hospital, maternal "attachment" is based on a mother's perception of her own childhood experiences. Now, Strathearn and his colleagues have used fMRI to reveal that the reward signals are stronger in mothers who had a secure attachment than in those who are less securely attached or dismissing.

"In a previous study, Strathearn and colleagues looked at how mothers in general responded to seeing their own babies smiling and the effects this had on brain biochemistry. The team has now looked at variations in groups of mothers to see if there are differences depending on how well the new mothers bonded with their own mothers.

The team explains that when a mother cradles her infant in her arms or plays with them, the more secure she is herself the more she tends to release more of the chemical oxytocin than those mothers whose scores on a standard test show them to be less securely attached.

Oxytocin is a well-known mammalian neurotransmitter commonly regarded as a key molecule in female reproduction. It is released in large amounts after distension of the birth canal during labour, and after stimulation of the nipples, which normally facilitates the processes of birth and breastfeeding.

The seemingly obvious connection between oxytocin release and feelings of well being in the mother and empathy towards the child tie in neatly with the compound's putative role in social recognition, pair bonding, anxiety, trust, love, and sexual pleasure.

"Our previous research has shown the importance of the mother-infant attachment relationship in human development," Strathearn adds. "We have observed significant differences in early maternal care-giving that we think may be linked with systems in the brain related to dopamine and oxytocin."

In the new study, the team hoped to find out how the brains of different kinds of mothers react to their infants. To accomplish this, they recruited first-time mothers in the third trimester of their pregnancies and monitored them for 14 months after their babies were born. Before the babies were born, the women took part in an interview that asked about childhood relationships with their parent or guardians. From those interviews, the researchers determined each woman's attachment pattern. Neither the mothers nor the researchers involved in the study knew the outcome of these interview analyses until the study was over.

The team also periodically (three times) monitored oxytocin levels and brain activity using fMRI when they showed pictures of the mothers' babies for 15 of the women reportedly having secure attachment and 15 of those who were insecure or dismissing. They recorded oxytocin levels before, during and after the mothers played with their infants in a typical setting.

The scans showed that seeing photos of their infants caused the brains of securely attached mothers to light up more (indicating greater activity) in the brain's reward centres than did the brains of the less securely attached mothers.

"Understanding the neurobiological processes underlying these differences in maternal behaviour may help us to indentify more effective treatment and preventive strategies for neglect or abuse," explains the paper's senior author Read Montague, professor of neuroscience and psychiatry and behavioural sciences and director of the Human Neuroimaging Lab at BCM.

The team worked with Peter Fonagy of University College London, UK and Janet Amico of the University of Pittsburgh School of Medicine with funding from the National Institute of Child Health and Human Development and the National Institutes of Health, the Kane Family Foundation, the National Institute of Neurological Disorders and Stroke, the National Institute of Drug Abuse and the Menninger Foundation.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.