Explorer Season 6

An extremely rare genetic disease passed down through generations, fatal familial insomnia's (FFI) primary symptom is sleeplessness, but with a fatal twist: victims are dead within months. National Geographic delves into the science of sleep to find out why we need sleep and what happens to us when we don't get it. Witness the pioneering research inside the sleeping brain as well as the mind forbidden to rest for days at a time.

Leonardo da Vinci's "The Battle of Anghiari" vanished 500 years ago, with only copies rendered by other artists left behind to confirm its existence. Scientist and art enthusiast Maurizio Seracini, has dedicated 36 years to tracking down the missing mural, and seems to be on the verge of uncovering the hidden fresco behind the walls of the Palazzo Vecchio in Florence, Italy.