Who's there? A radiologist studies digital X-rays in a viewing room at what is now called the Walter Reed National Military Medical Center in Bethesda, Md. Seth Rossman/U.S. Navy hide caption

itoggle caption Seth Rossman/U.S. Navy

The warmer orange colors show parts of the brain most active during improvisational rap. The blue regions are most active when rappers performed a memorized piece. NIDCD hide caption

itoggle caption NIDCD

Do you really need that MRI, or is your doctor just trying to make a buck? iStockphoto.com hide caption

itoggle caption iStockphoto.com