Forty percent of the global population suffers from headache disorders, and scientists don’t really know why. Tom Zeller Jr. is co-founder and editor-in-chief of Undark, a nonprofit digital magazine exploring the intersection of science and society. He joins host Krys Boyd to discuss why, with so many billions of people suffering, headache research is not a top priority in medicine, why it is so difficult to study and his own experience with debilitating cluster headaches. His book is “The Headache: The Science of a Most Confounding Affliction—and a Search for Relief.”