When her daughter was preschool-aged, Rebecca Spencer experienced something familiar to many parents and childminders: the power of a nap. Without it, her daughter would be giddy, grumpy, or both. Spencer, a neuroscientist focusing on sleep at the University of Massachusetts Amherst, wanted to investigate the science behind this anecdotal experience. “The observation of a lot of people is that a napless kid is emotionally dysregulated,” she says. “So that spurred us to ask this question of, ‘Do naps actually do something to process emotions?’”