NREMsömn

NREMsömn, or non-rapid-eye-movement sleep, is the Swedish term for the non-REM phase of sleep in humans and many mammals. It is one of the two primary sleep phases, alternating with REM sleep, and typically accounts for about three-quarters of total sleep in healthy adults. NREMsömn is characterized by progressive disengagement from wakefulness and physiological changes such as reduced metabolic rate and decreased responsiveness to external stimuli.

NREMsömn is divided into three stages. N1 is a light transitional stage between wakefulness and sleep, marked by a shift from alpha to theta brain activity and slow eye movements. N2 features sleep spindles and K-complexes on the electroencephalogram (EEG), with continued relaxation and a further drop in heart rate and body temperature. N3, also known as slow-wave sleep, is the deepest NREM stage, dominated by high-amplitude delta waves and marked by substantial muscle relaxation and reduced arousal threshold.

Physiologically, NREMsömn involves lower cortical activity than wakefulness but distinct thalamocortical patterns, autonomic stabilization, and enhanced restorative processes. Sleep cycles typically last about 90 to 110 minutes and repeat several times per night, with deeper NREM sleep more common earlier in the night and REM sleep increasing in later cycles.

Functions associated with NREMsömn include memory consolidation for declarative information, synaptic homeostasis, metabolic restoration, and clearance of neuronal waste via the glymphatic system. Clinically, disruptions to NREMsömn can contribute to insomnia, sleep apnea, and parasomnias such as sleepwalking and night terrors, which often occur during N3. Age-related changes frequently involve reduced depth and duration of NREM sleep. Diagnosis and staging rely on polysomnography, combining EEG with eye and muscle activity measures.