In the no-man’s-land between going to sleep and waking up, your brain goes through myriad states. On an electroencephalogram (EEG), or a readout of the brain’s electrical activity, scientists and doctors can tell each stage apart. But it is not totally clear what each one brings to the mix . Sleep relieves fatigue, allows the brain to process the events of the day, and appears to aid in memory and learning . But which stage does what? Answering that question may reveal how to get better quality