nietREMslaap

nietREMslaap, or non-REM sleep, is the portion of sleep characterized by reduced conscious awareness and slower brain activity compared with REM sleep. In most adults, non-REM sleep comprises three stages (N1, N2, N3) that cycle with REM periods throughout the night. NREM sleep tends to be most prominent in the first half of the night, while REM sleep increases in the later cycles.

Stage N1 is the transition from wakefulness to sleep and is considered light sleep. EEG activity shifts from alpha to theta waves; eye movements slow and may stop, and arousal is relatively easy. Stage N2 reflects deeper sleep and marks the onset of true sleep. It features characteristic EEG patterns, including sleep spindles and K-complexes, along with further slowing of heart rate and a drop in body temperature. Stage N3, often called slow-wave sleep or deep sleep, shows dominant delta waves and is the most difficult stage to awaken from. N3 is associated with restorative processes, reduced sensory responsiveness, and growth hormone release.

Functions attributed to non-REM sleep include memory consolidation for declarative knowledge, synaptic homeostasis, and metabolic clearance in the brain. The proportion and distribution of NREM stages can be influenced by age, sleep debt, and medications. Clinically, abnormalities in NREM sleep are linked to disorders such as insomnia, obstructive sleep apnea (which can reduce deep sleep), and NREM parasomnias (for example, sleepwalking and confusional arousals) that occur during N2 or N3. Non-REM sleep is a fundamental component of healthy sleep architecture and overall daytime functioning.