Children adopted from abroad often have difficulties adjusting to their new families and to life in the United States, exhibiting poor social skills, problems bonding with new family members and reticence in dealing with strangers.
Those difficulties are generally traced back to emotional deprivation in large orphanages, where infants often outnumber staff by 40 to 1, and caregivers do little more than feed and change the infants.
Now Wisconsin researchers have found that such deprivation can produce relatively permanent changes in a child's brain chemistry, impairing production of hormones, such as oxytocin, that are crucial to bonding and social interaction.
"This work makes a link between complex emotional behaviors and the developing brain," said lead author Seth D. Pollak, a psychologist at the University of Wisconsin.
But, he said, "It's extremely important that people don't think that this work implies that these children are somehow permanently delayed." Pollak and his colleagues reported their findings recently in the Proceedings of the National Academy of Sciences.
Many children adopted from abroad grow up to be perfectly normal, he noted.
"All we are saying is that in the case of some social problems, here is a window into understanding the biological basis ... and how we might design treatments," Pollak said.
Oxytocin, sometimes known as "the peptide of love," plays a crucial role in many social situations. Studies in animals have shown that increased levels are stimulated by pleasing sensory experiences, such as comforting touches and smells. As levels rise, animals - and presumably humans - form social bonds, display parent-child attachments and form memories of the experiences.
Another recent study in humans showed that spraying oxytocin into the nose can increase trust among strangers.
Children raised in orphanages where they don't receive contact with adults beyond the bare necessities aren't able to produce the hormone in such situations, interfering with their ability to develop normally, Pollak said.
The findings are important because about 200,000 children adopted abroad are now living in the United States and an additional 20,000 are brought in each year, a third of them from Eastern Europe.