[Normal sleep].
Level 5 - mechanism / opinion, no new human data
Narrative review without systematic methodology or primary empirical data
What was done
Narrative review summarizing the physiological structure of normal human sleep, the organization of non-rapid eye movement (NREM stages 1 through 4) and rapid eye movement (REM) sleep, and typical alterations in sleep architecture observed during normal aging.
What was found
The review outlines that sleep is organized into cycles lasting 90 to 110 minutes, with 4 to 6 cycles occurring per night and REM episodes lengthening toward morning. NREM sleep accounts for 70% to 80% and REM sleep accounts for 20% to 25% of the total sleep process. Normal aging is described as involving a reduction in slow high-voltage delta activity with relatively constant REM duration, along with an increased number of sleep stage shifts, increased awakenings, and a shift toward superficial sleep stages. The abstract provides no primary experimental data, sample sizes, or statistical tests.
Why it matters
It provides a baseline overview of normal sleep cycle parameters and age-associated architecture changes for clinical reference.
Limits
This is a brief narrative review without primary empirical data, defined study population, systematic search methodology, or quantitative error estimates.
Cited by
- supports Human sleep cycles repeat approximately every 90 minutes across the night.