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Researchers have found new evidence that maltreatment during childhood can lead to long-term changes in the brain. NPR's Jon Hamilton reports these changes could explain why abused children are much more likely to develop problems like anxiety and depression.

JON HAMILTON, BYLINE: Maltreatment can be physical or emotional and it ranges from mild to severe. So, researchers at the University of Wisconsin had a pretty typical group of 18-year-olds answer a questionnaire designed to assess childhood trauma. The young adults are part of a larger study of more than 500 families that has been tracking children's social and emotional development since 1994. Ryan Herringa says in this part of the research, adolescents were asked how strongly they agreed or disagreed with statements like these...

RYAN J. HERRINGA: When I was growing up I didn't have enough to eat, my parents were too drunk or high to take care of the family, I had to wear dirty clothes, or I thought my parents wished I had never been born, or somebody in my family hit me so hard that it left me with bruises or marks.

HAMILTON: There were also statements about emotional and sexual abuse. The researchers assessed 64 teenagers. Some had been maltreated, some hadn't. Then the scientists used a special type of MRI to measure connections among three areas of the brain involved in processing fear. One area is the prefrontal cortex, which orchestrates our thoughts and actions. Herringa says when it comes to fear, the prefrontal cortex gets a lot of input from the amygdala.

HERRINGA: The amygdala is really the brain's emotion and fear center.

HAMILTON: And it triggers the so-called fight or flight response when we encounter something scary. Herringa says messages from the amygdala, though, are often balanced by input from the hippocampus, which helps decide whether something is truly dangerous.

HERRINGA: So, for example, if you're at home watching a scary movie at night, the hippocampus can tell the prefrontal cortex that you're at home, this is just a movie, that's no reason to go into a full fight or flight response or freak out.

HAMILTON: At least that's what happens when there's a strong connection between the hippocampus and prefrontal cortex, and the fear circuitry is working correctly. But Herringa says brain scans showed that in adolescents who had been maltreated as children, the connection with the hippocampus was relatively weak. He says, in girls who had been maltreated, the connection with the amygdala was weak, too.

HERRINGA: And importantly, we found also that these weaker connections actually mediated or led to the development of anxiety and depressive symptoms by late adolescence.

HAMILTON: Herringa says that seems to explain something he sees in many young patients with anxiety and depression.

HERRINGA: These kids seem to be afraid everywhere. It's like they've lost the ability to put a contextual limit on when they're going to be afraid and when they're not.

HAMILTON: Greg Siegle, a psychologist at the University of Pittsburgh, says the new study is important for several reasons. For one thing, he says, many young people who have been maltreated don't realize that they are unlike their peers when it comes to fear and anxiety.

GREG SIEGLE: Maltreatment is a disorder where often people are not even aware of the extent of their symptoms.

HAMILTON: Siegle says having a way to measure the effects of maltreatment in the brain also could help doctors know whether therapy for their patients is working. At another level, he says, the study represents progress in a national effort to find objective tests to help diagnose and treat mental disorders.

SIEGLE: In psychiatry, in psychology, we very rarely have those tests because we just don't know the biological and brain mechanisms. This study for maltreatment is starting to get at what mechanisms we should be looking at.

HAMILTON: And Siegle says it's a reminder that even relatively mild maltreatment can do lasting harm. The study appears in the Proceedings of the National Academy of Sciences. Jon Hamilton, NPR News.

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