When you spend the night tossing and turning, your brain feels like a pile of mush the next day. No matter how hard you try to comprehend the new system they've adopted at work, it just won't compute. But why? Your brain is pretty high maintenance—in order to learn efficiently, it requires not only sleep, but deep sleep. For a study published in Nature Communications in 2017, researchers from Zurich, Switzerland developed a new, non-invasive way to disturb deep sleep in people's motor cortex. They recruited six men and women to sleep in the lab overnight, once with regular deep sleep, and again after a night of manipulated sleep. The day after each night of sleep, they were asked to participate in a "learning assessment" where they were trained to tap their fingers in a particular order. The participants felt like they had the same quality of sleep both nights, but there was a marked decrease in their ability to learn the new tasks after the night of disturbed sleep