Most current theoretical models of dreaming are built around an assumption that dream reports collected on awakening provide unbiased sampling of previous cognitive activity during sleep. However, such data are retrospective, requiring the recall of previous mental events from sleep on awakening. Thus, it is possible that dreaming occurs throughout sleep and differences in subsequent dream reports are owing to systematic differences in our ability to recall mentation on awakening. For this reason, it cannot be concluded with certainty that sleep cognition is more predominant or in any way different during REM compared to NREM sleep. It is our contention that REM sleep and ponto-geniculo-occipital (PGO) waves do not necessarily represent “pseudosensory” stimulation of the cortex in the generation of dreams, but might rather represent enhanced arousal of attention mechanisms during sleep, which results in the subsequent recall of attended mentation on awakening.

[Hobson et al.; Nielsen; Revonsuo; Solms; Vertes & Eastman]