What causes headaches?

In ancient Greece, the best-known remedy for a long-standing headache was to drill a small hole in the skull to drain supposedly infected blood. Fortunately, doctors today don't resort to power tools to cure headaches, but we still have a lot to learn about this ancient ailment. Dan Kwartler shares what we know (and don't know) about headaches. [Directed by Sharon Colman, narrated by Addison Anderson, music by Miguel d'Oliveira].