麻豆传媒

MADISON, Wis., Nov. 22 - Children raised in the uncaring environment of some eastern European orphanages ended up with a long-lasting deficit in two hormones involved in forming social bonds, reported researchers here.

In other words, nurture -- or the lack of it -- can trump nature when it comes to the ability to form social bonds, according to Seth Pollack, Ph.D., and assistant professor of psychology and of psychiatry and pediatrics at the University of Wisconsin.

The deficits in oxytocin and arginine vasopressin persisted even after the children were removed from the orphanages and placed with loving and stable families in Wisconsin, Dr. Pollack and colleagues reported in the Nov. 21 online edition of the Proceedings of the National Academy of Sciences.

The two hormones are known to play a role in the ability to form social bonds, Dr. Pollack said, and the deficit he and colleagues found is the first demonstration that early neglect can have a direct effect on neurobiology in ways that may later influence emotional behavior.

Normally, Dr. Pollack said, infants begin to bond with caregivers almost immediately after birth and it is difficult to separate the influences of social experience and biology on such complex behavior.

But the "aberrant social environments" of some orphanages in Russia and Romania -- where "a prominent lack of emotional and physical contact from caregivers" was standard -- provide a unique natural experiment, he and colleagues wrote.

They compared 18 four-year-olds who had spent an average of 16.6 months in the orphanages and who were then adopted by families in Wisconsin to 21 children who were living with their biological parents.

At the time of the study, the former orphans had been living with their new families for an average of 34.6 months.

A baseline analysis showed that the former orphans began with markedly lower levels of vasopressin than the control children. The difference was statistically significant at p<0.01.

That suggests, Dr. Pollack and colleagues said, that social deprivation may inhibit the development of the vasopressin system. Since the hormone appears to be critical for recognizing familiar people, that may in turn affect the formation of social bonds.

There was no difference in the baseline levels of oxytocin, which is thought to confer a sense of security and protection.

In the experiment itself, the children were asked to sit on the lap of a woman and play a 30-minute computer game that directed them to engage in various forms of physical contact, such as whispering, tickling, or patting each other on the head.

Each child played the game twice, once with his or her mother and once with a stranger.

After each game, the researchers collected a urine sample to measure oxytocin and vasopressin levels.

The study found:

• The control children tended to have higher levels of oxytocin than the former orphans after they interacted with their mothers. The difference approached statistical significance at p=0.056.
• There were no differences between the groups after the interaction with the unfamiliar adult.
• There were no differences in vasopressin between groups after either interaction.

Dr. Pollack said the results may help explain why many neglected children have difficulties forming secure relationships, but added it should not be taken as evidence that the damage is permanent.

"It's extremely important that people don't think this work implies that these children are somehow permanently delayed," he said. "All we are saying is that in the case of some social problems, here is a window into understanding the biological basis of why they happen."

The researchers also noted that the findings don't apply to all adopted children; those in this study were subjected to an unusually deprived environment.

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