Since 2016, a number of U.S. diplomats and federal employees have reported symptoms of a mysterious illness, the so-called Havana Syndrome.The list of symptoms include hearing loud sounds, nausea fatigue, and dizzying migraines, among others. The cause of this mystery illness is a source of curiosity, but it remains unknown.Last year the State Department commissioned a study by the National Academies of Sciences for researchers to investigate Havana Syndrome.NPR's Sarah McCammon spoke to Dr. David Relman, a Stanford professor who headed the investigation.One possible cause their group came to was a form of microwave radiation that occurs in a pulsed or intermittent form. In participating regions, you'll also hear a local news segment that will help you make sense of what's going on in your community.Email us at considerthis@npr.org.