From Time: Have you ever been so exhausted that you feel basically half-asleep? Turns out, that may be what's literally going on in your brain, according to a new study published in Nature. In a study of rats, researchers found that when the animals were deprived of sleep, parts of their brains (specifically, neurons in two areas of the cerebral cortex) switched into a sleeplike state, even while the rest of the brain stayed awake — and the rats themselves appeared completely alert. · Go to Does your brain take naps while you’re awake? →