Francis Csedrik remembers details of being bonked hard on the head when he was 4, and having to go to the emergency room. Meg Vogel/NPR hide caption

itoggle caption Meg Vogel/NPR

Michael Boatwright, an amnesia sufferer who now refers to himself as Johan Ek, during an interview at the Desert Regional Medical Center in Palm Springs, Calif. Jay Calderon/The Desert Sun hide caption

itoggle caption Jay Calderon/The Desert Sun