Slide 1
Sleep alternates among measured stages
Sleep alternates among stages with different patterns of brain activity. A sleeping brain is not simply switched off for the night.
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Sleep studies classify stages using physiological measurements, including electrical activity recorded from the scalp. These observations let researchers compare the organization of sleep across a night.
Slide 2
Non-REM sleep has three stages
Non-REM sleep includes three stages. The first is a transition from wakefulness, while the deepest is associated with prominent slow brain waves.
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REM stands for rapid eye movement; non-REM refers to the other sleep stages. Deep non-REM sleep is often more concentrated earlier in a night, while stage proportions change with age and other conditions.
Slide 3
REM combines rapid eyes with a different brain pattern
During REM sleep, rapid eye movements accompany an active brain pattern. Many skeletal muscles become much less active.
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Dreaming is strongly associated with REM, but dreams can also occur during non-REM sleep. Remembering a dream does not by itself identify precisely which stage preceded awakening.
Slide 4
Later cycles generally contain longer REM periods
Sleep stages recur in cycles, but the cycles are not identical. REM periods generally become longer toward the later part of the night.
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A recording can also show brief awakenings and transitions. The architecture of a night is richer than a simple count of hours between lying down and getting up.
Slide 5
Stage labels guide research rather than describe a switched-off brain
Sleep-stage labels summarize measured patterns. They help researchers ask how sleep relates to memory, development and health.
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A wearable estimate is not identical to a laboratory recording of brain activity. Interpreting a person’s sleep requires attention to how the data were collected and the question being asked.
Sources
- Sleep Phases and Stages
NHLBI, NIH
- What happens during sleep?
NICHD, NIH