Sleep cycle

In sleep research and sleep medicine, the sleep cycle describes the sequence of sleep stages during sleep .

Hypnogram with a sleep cycle - after a short "lying awake" (W) there was some light sleep (N1), interrupted by waking up again, then some sleep of stages N2 and extensive deep sleep (N3) as well as 13 minutes of REM sleep (R)

Healthy people have four to seven sleep cycles of around 70–110 minutes each night (90 ± 20 minutes, ultradian rhythm ), during which the NREM stages N1, N2 and N3 and again N2 followed by REM sleep are passed through .

The different phases of sleep are characterized by different characteristics and correlated brain activities:

The N1 and N2 indicate a light sleep phase, with slow to no eye movements, the heart rate and body temperature are reduced, and mainly theta frequencies (4–8 Hz), including sleep spindles and K-complexes, are measured.

During the N3 and N4 phases it is difficult to wake up, the body is relaxed, the EMG is greatly reduced and one is in deep sleep, with delta frequencies (0.5-3.5 Hz) being dominant.

All of these phases characterize the N-REM phase, with the REM (rapid eye movement) phase being characterized by the rapid phasic eye movements. There are low EMG amplitudes and theta and occasionally alpha frequencies in the brain. REM is also the phase of sleep where dreams take place.

In the following cycles, the proportion of deep sleep decreases and disappears completely in the later cycles. In contrast, the REM percentage increases towards the end of sleep.

The proportions of the total duration of a night's sleep are distributed as follows in a healthy person of middle age (approx. 30 years):

Stage N1 at about 5%
Stage N2 in about 45-55%
Stage N3 in about 15-25%
REM sleep at around 20-25%
Wakefulness below 5%.

The assignment of time segments of sleep to the sleep stages takes place during the evaluation of the measured values obtained by means of polysomnography and is shown in the sleep profile (also: hypnogram).

Significant deviations from this basic pattern often lead to sleep being perceived as less restful. Sleep-interrupting wake reactions such as the arousals in sleep apnea syndrome , as well as changes in the sequence. Special features such as REM sleep a few minutes after falling asleep, so-called sleep-onset REM periods (SOREMP), can be indications of certain sleep disorders .

literature

American Academy of Sleep Medicine (Ed.): The AASM Manual for Scoring Sleep and Associated Events. Rules, technology and technical specifications . 1st edition. Steinkopff-Verlag, Heidelberg 2008, ISBN 978-3-7985-1851-3 .
H. Peter, T. Penzel: Encyclopedia of sleep medicine . Springer, Berlin / Heidelberg 2007, ISBN 978-3-540-28839-8 .

Individual evidence

↑ Peter, Helga .: Encyclopedia of Sleep Medicine . Springer, Berlin / Heidelberg 2007, ISBN 978-3-540-28840-4 ( worldcat.org [accessed January 27, 2020]).
↑ Conrad Iber, Sonia Ancoli-Israel, Andrew L. Chesson, Stuart F. Quan: The AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology, and Technical Specifications . Ed .: American Academy of Sleep Medicine. AASM, Westchester, Ill. 2007.
↑ Hans-Günter Weeß: Phenomenology, function and physiology of sleep . In: Psychotherapy in dialogue . Vol. 10, No. 2 , 2009, p. 101-106 , doi : 10.1055 / s-0029-1223312 .

[1] Peter, Helga .: Encyclopedia of Sleep Medicine . Springer, Berlin / Heidelberg 2007, ISBN 978-3-540-28840-4 ( worldcat.org [accessed January 27, 2020]).

[Scoring2007-2] Conrad Iber, Sonia Ancoli-Israel, Andrew L. Chesson, Stuart F. Quan: The AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology, and Technical Specifications . Ed .: American Academy of Sleep Medicine. AASM, Westchester, Ill. 2007.

[pid-3] Hans-Günter Weeß: Phenomenology, function and physiology of sleep . In: Psychotherapy in dialogue . Vol. 10, No. 2 , 2009, p. 101-106 , doi : 10.1055 / s-0029-1223312 .