Why We Sleep

You may think it's for your body, but it's really for your brain. The latest research is full of surprises

Maybe you have a big report due first thing in the morning. Or you're trying to deliver a truckload of fish before the wholesale market opens 150 miles away. Whatever the reason, you decide to stifle that yawn and push through the night. Sure, you've been awake 16 hours, but you have a giant thermos of coffee and a few tunes to keep you going. Your body, of course, is fighting you every step of the way. Whether or not you realize it, your brain has already started to check out for the night.

That yawn was the first sign that...

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