NREM Sleep.
NREM sleep or Non rapid eye movement sleep is a dreamless sleep and is also called the quiet sleep. This stage of sleep consists of four stages each being deeper than the previous one. N1, N2, N3 and the 4th stage of NREM sleep which is also known as the delta sleep or slow wave sleep. In NREM sleep, as the stages of sleep progress the brain waves become slower and more synchronized. NREM sleep forms an important part of the sleep cycle.
On EEG, the brain waves during NREM sleep are typically slow and of high voltage. The sleeper is still and the blood pressure is low and there are no eye movements as seen in REM sleep. About 80% of your sleep hours consists of NREM sleep. NREM sleep lasts for 4 to 6 hours during the night that you sleep while REM sleep lasts for only 2 hours.
Stages of NREM Sleep.
Stage N1 – Transition to sleep.
This is light sleep which lasts briefly for 5 to 10 minutes. It is a transition from wakefulness to sleep. You are easily awakened in this stage of sleep and when awakened you may feel that you were not asleep at all. During this stage, the muscle activity slows down and the eyes move slowly under the closed eyelids.
In this stage you may experience sudden jerky movements of some muscles, giving a sensation of falling down from the bed. These are called myoclonic jerks and are caused by the spontaneous stimulation of the motor centers of the brain. On EEG, this stage produces theta waves which are high amplitude slow waves.
Stage N2 – Stage of light sleep.
This is the beginning stage of true sleep which lasts for 10 to 25 minutes. In this stage, there are no eye movements, heart rate slows down and body temperature decreases. About 50 % of the sleeping time is spent in this stage. Brain waves become slower indicating slower brain activity. However there will be brief bursts of rapid and rhythmic brain activity shown by sleep spindles on EEG. Sleep talking usually occurs during stage N1 and N2.
Stage N3 – Stage of transition to deep sleep.
This is a stage of transition from light sleep to deep sleep and it is difficult to awaken a person from this stage and if awakened the person is groggy and disoriented for a few minutes. Blood is directed away from the brain to the muscles to restore physical energy. Deep slow brain waves called delta waves emerge during this stage combined with fast waves. During this stage your blood pressure and heart rate decline.
Stage of delta sleep.
This is so called because of the exclusive high amplitude low-frequency delta waves which are seen in this stage. This is a stage of deep sleep which lasts for about 30 minutes. Sleep walking and bedwetting occur toward the end of this stage of sleep. Stage N3 and this stage are important for a satisfying sleep and to feel refreshed in the morning.
Though NREM is a dreamless sleep, it is found that you do dream in the 3rd and 4th stage of this sleep than in the other NREM stages, though not as commonly as in REM sleep. The dreams of this deep sleep stage of NREM sleep tend to be disconnected, less clear and less memorable.
Picture showing NREM sleep stages.
As of 2008, Stage N3 and the stage of delta sleep (stage 4) were combined to form one stage labeled as N3 or the third stage which is the stage of deep sleep by American Academy of Sleep Medicine (AASM). NREM sleep is therefore now considered by many as having three stages only.
NREM and REM Sleep.
NREM sleep and REM sleep are both important. Both are required to rest the body fully. Without one, the other would be ineffective.
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