In a study that could offer a glimpse into sleep's still poorly understood functions, researchers have identified genes upregulated specifically during sleep.[1] The findings contain surprises, investigators say. One is simply that there are many such genes, at least as many as are turned on while awake, belying the common-sense view that sleep implies inactivity. Another is that the sleep-related changes in gene expression extend to the cerebellum, a structure not previously known to participate in sleep.