Dr. Bruce Perry, a child psychiatrist, says neglected children's brains develop differently.

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Dr. Bruce Perry is a world-renowned child psychiatrist and the author of The Boy Who Was Raised as a Dog, one of the foremost books on extreme child abuse. Oprah says he's also the first person she called when she had a crisis at the Oprah Winfrey Leadership Academy in 2007.

While extreme cases of child neglect may make headlines, Dr. Perry says these examples are just the tip of the iceberg. "Most people don't realize this, but there are twice as many neglected children in the United States as there are physically and sexually abused combined," he says.

Dr. Perry says at least 500,000 children every year are neglected by their caregivers. "It's like a silent epidemic," he says. "From a functional perspective for the developing child, neglect is the absence of necessary stimulation required to build a certain part of the brain so it can function normally."

When a child doesn't get enough stimulation early in life, Dr. Perry says the brain may develop differently. "That changes all kinds of functions, including the ability to form and maintain relationships," he says.