Underwater explorer and photographer Jill Heinerth has dived into unmapped caves deep in the earth, and beneath a giant iceberg. She's seen hidden creatures old as dinosaurs, and witnessed scenes of surreal beauty. Her work is so dangerous, over a hundred of her friends and colleagues have died in caves. She talks about the risks and rewards of her work.
We tend to think of being asleep or awake as an either-or prospect: If you're not asleep, then you must be awake. But sleep disorder specialist and neurologist Guy Leschziner says it's not that simple.