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Since REM sleep is the phase during which dreaming occurs, the scientists speculate that this absence of memory-consolidating chatter may eventually help to explain why dreams can be so difficult to remember.

By listening in on the chatter between neurons in various parts of the brain, researchers have taken steps toward fully understanding just how memories are formed, transferred, and ultimately stored in the brain- and how that process varies throughout the various stages of sleep. Researchers don't know for sure why dreams are easily forgotten. Maybe we are designed to forget our dreams because if we remembered all our dreams, we might not be able to distinguish dreams from real memories.

Also, it may be harder to remember dreams because during REM sleep our body may shut down systems in our brain responsible for creating memories. We may only remember dreams that occur just before we wake, when certain brain activities have been turned back on. Scientists have long known that memories are formed in the brain's hippocampus, but are stored elsewhere--most likely in the neocortex, the outer layer of the brain. Transferring memories from one part of the brain to the other requires changing the strength of the connections between neurons and is thought to depend on the precise timing of the firing of brain cells.