Some animals do it for survival, while others have evolved this ability for different reasons. It might seem strange, but these animals have developed abilities to rest while staying alert to their ...

Every animal with a brain needs sleep. A few creatures without one do, too; even jellyfish enter a sleep-like state.

This story was originally published by CalMatters. Sign up for their newsletters. If you’re serving hard time inside a California prison, you’ll often find yourself stuck in a cramped cell with a ...

Have you heard the saying about “sleeping with one eye open”? It’s a bit of metaphoric advice about staying vigilant—and a way to describe very light restless sleep. But sleeping with eyes open is ...

A recent study observed sleeping participants' pupils during sleep, using a new method that could have implications for studying sleep disorders. Reading time 2 minutes Though sleep is a time to power ...