Studying the firing patterns in various brain regions of dreaming mice have challenged our theories about dreams.
In this study, they were surprised to find: "that the interaction occurred in a surprising way: Instead of the hippocampus uploading information to the neocortex, the opposite is true. The neocortex seems to drive the dialogue."
The hippocampus is responsible for forming new memories, and spatial navigation . The neocortex has many functions, including conscious thought.
Here is one new hypothesis from the findings of this study: "Memories may not be stored during sleep at all, but while humans are awake. The role of sleep, he suggested, may be to erase memories in the hippocampus as a way of creating a fresh page for the brain’s scratch pad.
“All of this research raises more questions than it answers,” Mehta said. “But we do know this: How we make and store memories is a more complex process than we thought.”".
For more details of the study: http://www.sciencedaily.com/releases/2007/03/070305202818.htm