I'm just going to throw my opinion in here to clear up some misconceptions. The brain scans show that psychopaths cannot feel true emotions, not that they can't change their behavior. They can change their behavior, and most of them are very, very good at it. Superficial charm is one of the criteria. But, like Michael said, it doesn't last, especially in close relationships where that mask is put under close scrutiny. They can't change the fact that their behavior isn't sincere. They can't really feel the emotions that go along with that behavior. It's all a facade, and that's one of the reasons why psychopathy is such a stigmatized disorder.