Recent research into chronic pain, which afflicts millions of Americans, has led to a surprising source: the brain. “Sunday Morning” host Jane Pauley talks with Dr. Sanjay Gupta (a neurosurgeon and chief medical correspondent for CNN) about his new book, “It Doesn’t Have to Hurt,” and about the body’s defenses against pain. She also talks with heavy metal musician Ed Mowery, whose decades-long experience with complex regional pain syndrome (or CRPS) led to a revolutionary surgery and treatment.