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

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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

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NIDCD

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

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iStockphoto.com