REM sleep is important in memory consolidation. However, the idea that only REM sleep and no other stage of sleep is important in memory consolidation was a result of some of the early studies during the 1970s and 1980s that demonstrated that REM sleep would increase after learning but the same increase would not be seen for slow wave sleep.
What evidence do we have that dreaming has anything to do with the consolidation of memories? The idea stems from the notion that if a dream reflects events recently experienced while awake, it may be that the rehearsal of learned information in dreams results in their consolidation into memory.
Some of the most impressive research on REM sleep and memory to date is that of REM sleep windows. The nutshell of what this research shows is that there are specific time windows following learning during which REM sleep must be allowed to occur in order for the consolidation of memory to occur.
Back in 1885, a researcher named Ebbinghaus was interested in how long it takes the brain to consolidate memories. He wanted to determine the optimum time required in the consolidation of a memory, but he was concerned that if actual words were used, participants in the study may be more or less familiar with certain words which could then affect the ease or difficulty of learning them.
Although dream imagery can occur during other stages of sleep, Rapid Eye Movement (REM) sleep is loosely known as dream sleep. The hallmarks of REM sleep are a low voltage mixed frequency EEG, low muscle tone, and bursts of rapid eye movements punctuated by periods when the eyes remain relatively motionless.