REM and NREM Sleep Mentation Differences: A Question of Story Structure?

Dreaming is an expression of vivid imagery with a seemingly storylike structure (1-3). Early observations (4,5) temporally linked vivid dreaming with REM sleep, an association which many took to be an exclusive one (e.g., 6-8). However, when the definition of dreaming was expanded to include more general forms of cognition (9), more serious consideration was given to the notion that dreaming is also a feature of NREM sleep. Indeed, dozens of studies reported evidence that awakenings from any NREM stage can produce recall of cognitive activity and in many instances recall of mentation that appears wholly dreamlike (for review see 10). Opinions are still mixed, however, as to whether the quality of mentation occurring in REM and NREM sleep stages is, in fact, identical. Whereas many have reported qualitative differences between the two types of mentation (for reviews see 10-12), many such differences are diminished when steps are taken to statistically control the length of reports REM and NREM Sleep Mentation Differences: A Question of Story Structure?