For pathological liars -- eg., those who do it so often they can't help themselves, it's an integral part of their lives, their identity, etc. -- I think this is pretty surprising (to me, anyways). It's an interesting behavior and while it's easy I think to point to some brain tumor or something, the view I subscribed to was this was learned behavior -- the person was reinforced early in their lives for lying (e.g., they found they could get away with stuff, rewards, etc.).

This study indicated their brain is wired a little differently from the rest of us, increasing their likelihood to lie and not feel any inhibition about doing so...

Interesting stuff....
DocJohn