With ever more refined techniques for measuring complex brain activity, scientists are challenging the understanding of thought, memory and emotion–what we have traditionally called “the self.”

We spend a third of our lives asleep. Every organism on Earth—from rats to dolphins to fruit flies to microorganisms—relies on sleep for its survival, yet science is still wrestling with a fundamental question: Why does sleep exist?

Intelligence was once thought to be uniquely human. But researchers have discovered astonishing cognitive abilities in many other species—not just our close cousins like chimps, or fellow mammals like dolphins—but …

This video is part of our Brilliant Breakthroughs series: our new 20-episode mini-series exploring the “Eureka!” moments and proud accomplishments of the greatest scientific minds of our time. Join us …

What made Albert Einstein one of the greatest scientific geniuses the world has ever known? His scientific breakthroughs revolutionized the way we understand the universe.

What’s it like to face a faceless world? Acclaimed neurologist Oliver Sacks once apologized for almost bumping into a large bearded man, only to realize he was speaking to a mirror.