Seth Pollak, a psychologist at the University of Wisconsin, led a research team that compared the progress of children raised by their biological parents with children who had come from crowded orphanages in Russia and Romania and had been adopted by parents in the US. "When these [orphanage] children were babies there were so few adults around that there was rarely one available to respond to their needs," Dr Pollak said.

The children studied had an average age of 4½ years, and the orphans had been settled with their foster parents for two years and 10 months on average. Eighteen of the 39 children studied were from orphanages. They were observed at home playing interactive games and sitting on their mother's lap.

Before and after this physical contact, the children provided a urine sample to measure levels of two hormones: vasopressin, thought to help us recognise familiar individuals and live in social groups; and oxytocin, the release of which makes us feel secure and protected.

It was discovered that the children from orphanages had lower underlying levels of vasopressin and, unlike children raised by their biological parents, their levels of oxytocin did not rise with cuddling. "It is remarkable that the children's deficiencies in these affection hormones could still be detected now, after they had spent three years in loving adoptive homes," said Terrie Moffitt, a developmental psychiatrist at King's College London. "An unanswered question is whether or not the hormonal deficiencies will result in any behavioural difficulties for the children in the long term."

The researchers suspect that if deprived of close adult contact soon after birth, children will never fully develop the brain pathways. "It used to be thought that the brain came all wired up, but now it seems that social experiences after birth are vital for opening up the pathways and strengthening the connections in the brain for these hormones," Dr Pollak said. The research team plans a follow-up study with the same children to see if this is the case. He also speculates that giving children plenty of cuddles at birth leads to an "addiction" to close relationships in later life.

"The area of the brain that acts as the receptor for oxytocin is also the reward centre associated with drug addictions. It is possible that close relationships function like an addiction, making us go and seek them out in later life," he said.

Report by Kate Ravilious in London
November 23, 2005

Full research article:

Early experience in humans is associated with changes in neuropeptides critical for regulating social behavior, Proceedings of the National Academy of Sciences, November 22, 2005, vol. 102, no. 47, 17237-17240.