Scientists have long pondered why we sleep. Despite being nearly ubiquitous across the animal kingdom, the exact role of slumber remains an open question. While multiple studies suggest that, in both rodents and humans, it helps consolidate previously learned memories, the question of whether new information can be learned while snoozing has yet to be answered. A study published today (August 8) in Nature Communications reports that the sleeping brain can learn new information, but only during rapid-eye movement (REM) sleep, the stage when dreams typically occur.