It only took one mean comment from a classmate to send Caroline down a dangerous road.
"A girl called me fat. I stopped eating because I thought I was fat and I thought it was true," said Caroline. "So I wanted to make myself skinnier."
At 9 years old, she weighed 50 pounds. A healthy girl should weigh twice that. In the hospital and hooked up to a feeding tube, doctors told Caroline she was killing herself.
"That kind of made me break out in tears because I didn't really want to die," said Caroline.
Studies using MRI imaging of anorexic brains are turning the world of eating disorders upside down.
Psychiatrist Dr. Walter Kaye says traits that contribute to developing anorexia are genetic.
"Heritability is a much more powerful influence than culture is," Dr. Kaye said.
What's the difference between an anorexic brain and a healthy one?
In one study, participants were given a taste of sugar. In healthy people, the insula and frontal cortex areas of the brain lit up, signaling "Wow, that tastes good." That pleasure light didn't turn on in the anorexic's brain.
Dr. Kaye says they may literally not recognize when they're hungry or when something tastes good.
"Which actually may explain why it's possible for them to lose so much weight," said Dr. Kaye.
Studies helping doctors and patients see and understand a mysterious problem.
"There's really a very powerful biology that's driving this eating behavior," said Dr. Kaye.
Caroline is now at a healthy weight. "I had to keep on eating or else I wouldn't get any better," she said.
Dr. Kaye and others are now using their brain scan studies to develop new treatments that target the biology -- not just the psychology -- of eating disorders.
He says anorexics have many of the same personality traits, including attention to detail, concern about consequences and a drive to accomplish and succeed.