Sleep phases
All about sleep phases
What phases of sleep are there?
Human sleep is a complex process consisting of different sleep phases that are repeated throughout the night. These phases play a crucial role in the recovery and regeneration of the body and mind. Each phase has its own significance and the duration of sleep phases varies throughout the night. Sleep is divided into two main categories: Non-REM sleep (NREM) and REM sleep. NREM sleep itself is divided into three stages (1, 2 and 3), ranging from light to deep sleep, while REM (Rapid Eye Movement) sleep is responsible for most dreams.
The sleep phases
Light sleep (NREM phase 1)
This phase is the transition between the waking state and sleep. It only lasts a few minutes and is characterized by slow eye movements and decreasing muscle tone. During this phase, the body is still influenced by external stimuli, so people can wake up easily. Sometimes hypnotic twitches or a sudden “fall” occur at the beginning of this phase, which is a typical phenomenon of falling asleep.
Light sleep (NREM phase 2)
This phase accounts for around 40-50% of the entire sleep. The body temperature drops and the heart rate slows down. During this phase, rapid and short brain waves occur, which serve as a kind of protective mechanism to protect the brain from external disturbances and facilitate the transition to deeper sleep. The phase lasts around 20 minutes and is important for processing experiences and reinforcing new information in the memory.
Deep sleep (NREM phase 3)
During this phase, the body sleeps most deeply and recovers the most. The brain produces slow waves that characterize deep sleep. This phase is particularly important because this is when the body regenerates best, releases growth and healing hormones and strengthens the immune system. Deep sleep is the most restorative sleep phase and it is very difficult to wake someone in this state.deep sleep (NREM phase 3).
REM sleep (Rapid Eye Movement)
The last phase of sleep, the REM phase, is the one in which most dreams occur. The eyes move jerkily while the body is in a kind of “paralysis” to prevent us from physically acting out our dreams. This phase is particularly important for memory and emotional processing. During the REM phase, the heart rate increases and breathing becomes more irregular. On average, the REM phase lasts between 1.5 and 2 hours and increases in duration as the night progresses.
Duration and sequence of sleep phases
A complete sleep cycle lasts around 90 to 120 minutes, with the body going through all phases – from light NREM sleep to REM sleep. The progression of these phases changes throughout the night: At the beginning of the night, deep sleep (phase 3) is longer, while the REM phases tend to be shorter. The further the night progresses, the longer the REM phases last, while the deep sleep phases become shorter. On average, a person goes through about 4 to 5 cycles per night, which means that the sleep phases total about 6 to 8 hours in a normal sleep pattern.
Sleep phases in babies
The sleep phases of babies are slightly different from those of adults. Newborns sleep between 16 and 20 hours a day, although their sleep is not yet fully structured. They are often in a state that corresponds to REM sleep, as the body and brain are still developing and sleep contributes to essential development processes.
From around four months, the sleep rhythm of infants (4 months to 1 year) begins to stabilize. They still spend a large part of their time in REM sleep, which is important for their brain development. A typical infant sleeps about 12-16 hours per day, with several naps supplementing the night sleep.
Toddlers (1-3 years) usually sleep 10-13 hours per day. The proportion of deep sleep (NREM phase 3) is relatively high, which is crucial for growth and recovery. Afternoon naps become less and less, but these hours are still important for their development.
