This is the 2007 version. Click here for the 2017 chapter 03 table of contents.

Dreaming and REM sleep: Not the Same Thing

Dreams occur in both REM and non-REM sleep, if the word dream refers to mental processes during sleep that a person can report upon awakening. REM periods apparently stimulate dreaming because REM sleep is a very active state accompanied by all sorts of biological changes. But brain-scanning studies suggest that dreaming itself, as experienced by humans, occurs in a circuit involving the prefrontal cortex. Activity in that area correlates 100% with dreaming in subjects awakened suddenly and asked about their mental activity. REM sleep correlates "only" 70-80% with dream activity—still a high number.

How often do subjects report mental activity, when awakened from REM or non-REM sleep?

A classic finding from the Golden Age of Sleep Research is that very different sorts of dreams occur in REM and non-REM sleep stages. Judges presented with dream reports from REM and non-REM sleep have no trouble sorting them into two piles with high accuracy. The weird stories are almost always REM dreams; the fragments of normal thought are almost always non-REM dreams. In other words, REM dreams are like a narrative or story in which one is a believing participant. This feeling of participating in another world, an alternative reality as it were, perhaps indicates that the executive circuits of the forebrain must be engaged in some way during this type of dream.

What are typical qualities of REM and non-REM dreams?

Non-REM dreams, by contrast, feel like ordinary thinking. They are not like being in a different world; they are like thinking about recent events. People in non-REM sleep sometimes deny they have been sleeping at all, even when they have been snoring with their eyes shut, perhaps because their thoughts were so similar to normal waking thoughts.

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