Imagine an America that has been plagued for years by a mysterious epidemic of insomnia — an affliction so serious that many are dying from lack of sleep. That's the futuristic premise of Karen Russell's new novella, Sleep Donation.

What happens in our brains while we're asleep? That's one question neuroscientist Penelope Lewis is trying to answer. She directs the Sleep and Memory Lab at the University of Manchester in England. Her new book is The Secret World of Sleep: The Surprising Science of the Mind at Rest.

Lewis joins Fresh Air's Terry Gross to talk about how sleep affects memory, and how REM sleep can affect depression.

Interview Highlights

On how sleep makes memory stronger

Roger Rossing/Deutsche Fotothek / Wikimedia Commons

A scientist at Spokane’s Riverpoint campus has received a large grant to study one question: why do humans sleep?