White Matter

NPR:

If you could look into this part of the brain, which sits right behind your forehead, you would see two kinds of matter: gray and white. Gray matter is the groups of brain cells that process information. Most neuroscience studies focus on gray matter. But nearly half the brain is composed of connective tissues that carry electrical signals from one group of neurons to another. This is white matter. Roughly, gray matter is where the processing happens, and white matter connects different parts of the brain, helping us to bring different ideas together.

The liars in Yang's study had on average 22 percent to 26 percent more white matter in their prefrontal cortex than both the normal and antisocial controls.

More Connections

Yang speculates that the increase in white matter means that people who lie repeatedly and compulsively are better at making connections between thoughts that aren't connected in reality — like, say, "me" and "fighter pilot."