Here's a little Brain 101: The amygdala is the part of your brain helps you identify and "read" faces, something known as joint attention. "When you see a face, you scan it, identify if it's friend or foe and make a decision about whether to move forward or avoid it," neurologist Dr. Barry Kosofsky recently told CNN.

That small part of the brain might help researchers make big gains in autism intervention. Joint attention is an important characteristic of autism, and a recent study found that by age two, the amygdala is up to 13 percent larger in children with autism.

"Many studies have observed the brain grows too big in kids with autism, but this study finds that by age 2, the amygdala is already bigger and stops growing," says Kosofsky. "So it tells us the critical difference has already developed. It now poses the question: Are children born with autism or does it develop in the first two years of life?"

It's an exciting time, says Autism Support Network co-founder Brian Field. Autism is the fastest growing developmental disability, but researchers haven't been able to determine the exactly when and how autism starts. "Being able to assess infant and toddler brain development through MRI scans could one day become and expected diagnostic test for all children, and could help parents jump-start therapeutic services at an even earlier age," says Field. Early intervention services are crucial to children with autism.

Neurologist Dr. Robert Melillo, author of the book "Disconnected Kids," says that it's unlikely autism is related to just one area of the brain. But he thinks this study makes an important point. "What this does show is that the brain is not damaged or degenerated in any way, but certain areas are not maturing in the proper way. The amygdala seems to be an important area that is not maturing properly."

While this finding doesn't solve the mystery of autism, researchers feel like they've found an important piece of the puzzle.