The brain is a mysterious organ, locked in a bony case and all but inaccessible to the world. Until recently, if you wanted to look at the brain, you had to wait until people died, or snatch glimpses during brain surgery. Much of what was known came from trying to match symptoms seen during life with structural damage observed during autopsy. That's what Anne Foundas did.
Many kids stutter for a while, but then recover.
So Foundas took MRI images of the brains of 16 people with PDS, and compared them with 16 people with normal fluency. The two groups were carefully matched to try to eliminate any extraneous factors, such as handedness or sex. In Foundas's study, the stutterers tended to have a more symmetric planum temporale, although the region was larger overall. The stutterers in the study tended to have several extra gyri. Not every stutterer had all those odd features, Foundas said, but they all had some.