Oxytocin, a hormone that is involved in a range of psychological processes, plays an important role in social relationships, such as the development of the bond between a parent and child, and the formation of trust, and social understanding, across the lifespan.

For the research, published in Development and Psychopathology, 62 new mothers aged between 23 and 44 years old, and who had an infant between three and nine months old, were filmed interacting naturally with their baby for five minutes.

The researchers analysed the videos to see how well the mother accurately referred to her infant’s internal experience (e.g., their thoughts, feelings, desires and perceptions) during the interaction.

They also collected saliva samples from the infant and measured the level of the hormone oxytocin.

When the relationship between these two measures was analysed, the researchers found a positive correlation.

Lead author, Dr Kate Lindley Baron-Cohen (UCL Psychology & Language Sciences), said: “It has long been known that the hormone oxytocin is involved in intimate social relationships, including the attachment bond between a mother and her child. It is also known that how well a mother is attuned to her infant’s thoughts and feelings in the first year of life is a long-term predictor of the child’s social and emotional development. But the pathways underlying these effects have been unclear.

“We have, for the first time, discovered that the amount that a mother talks to their infant about their infant’s thoughts and feelings is directly correlated with their infant’s oxytocin levels. This suggests that oxytocin is involved in regulating children’s early social experience, and this is itself shaped by the way a parent interacts with their infant.”

For example, when a child demonstrates interest in a toy, a parent who displays understanding of their child’s internal state might say “Oh, you like this toy” or “You’re excited” and might imitate their child’s actions or facial expression. In this way the parent is mirroring the child’s internal experience, and the new results now reveal that this influences the infant’s oxytocin system as well.

The team also found that mothers who were experiencing postnatal depression referred less to their infant’s internal states than mothers who were not experiencing depression.

Dr Lindley Baron-Cohen said: “This study demonstrates a new psychobiological link between mothers and their infant, in which the mother’s emotionally sensitive speech is reflected in her infant’s hormone levels.

“This highlights the key role mothers play in their child’s early development, and indicates how mothers who are experiencing depression could be supported to facilitate their child’s social development.”

This research was funded by the National Institute for Health Research (NIRH) ARC North Thames, the Lord Leonard and Lady Estelle Wolfson Foundation, Wellcome Trust, the University of York, the Fund for Psychoanalytic Research through the American Psychoanalytic Association, the International Psychoanalytical Association, the Michael Samuel Charitable Trust, the Denman Charitable Trust, and the Galvani Foundation.