Reactive oxygen species in the guts of flies glow depending on the concentration of the molecules.Credit: Alexandra Vaccaro and Yosef Kaplan DorWhen neurobiologist Dragana Rogulja began studying sleep in her laboratory at Harvard Medical School in Boston, Massachusetts, in 2013, she had no idea what her experiments would tell her about how sleep affects the body. She wasn’t assuming — as many people do — that it’s a function mainly of the brain. She was just starting her lab and decided to throw...