Feature interview: Why do headaches remain such a mystery?

Headaches. We all get them. Yet despite centuries of study, we still don't really understand their causes and cures. Author and journalist Tom Zeller Jr has spent years trying to understand the kind of epic headaches he gets. He says he goes into the dark valley of head pain on a regular basis. He's on a quest to understand the stubborn pain he and a billion other people endure and why headaches remain such a mystery and what might finally offer hope. His book is called The Headache: The Science of a Most Confounding Affliction-and a Search for Relief.