Scientists have long known that while we sleep, our hippocampus replays many of the day's events and consolidates what happened into memories. It works the same way for rats, and the researchers wanted to know if they could use the audio cues embedded in the day's memories to influence the progression of a dream. It turns out they can. Analysis showed that when lab rats dream (at least these lab rats), they dream of mazes. And if the researchers played the audio chimes to the rats while they were dreaming, they would immediately begin dreaming of the section of the maze associated with that particular chime.