Research from the University of Rochester provides direct evidence for why your brain cells need you to sleep, and sleep the right way. The study found that when you sleep, your brain removes toxic proteins from its neurons that are by-products of neural activity when you're awake. Unfortunately, your brain can remove them adequately only while you're asleep. So when you don't get enough sleep, the toxic proteins remain in your brain cells, impairing your ability to think. Which is something no amount of caffeine can fix.