SlowWaveSchlaf

Slow Wave Sleep, known in German as SlowWaveSchlaf, is the deepest phase of non-REM sleep. It is defined by slow, high-amplitude delta waves on electroencephalography and by reduced physiological arousal compared with lighter sleep stages. In modern sleep staging it corresponds to non-REM stage N3.

During Slow Wave Sleep, heart rate and breathing slow, blood pressure is lower, and muscle tone is reduced with minimal eye movements. The brain shows prominent delta activity in the range of about 0.5 to 4 Hz, reflecting synchronized neuronal activity. This stage typically occurs in the first half of the night and becomes progressively shorter across sleep cycles.

Slow Wave Sleep plays several key roles. It is important for the consolidation of declarative memories and for synaptic downscaling, a homeostatic process that helps restore neural networks after wakefulness. The glymphatic system, which helps clear metabolic waste from the brain, is particularly active during SWS, contributing to brain maintenance.

The amount of Slow Wave Sleep is influenced by age, sleep pressure, and health. It tends to be most prominent in children and decreases with age. Sleep deprivation increases delta power and SWS duration during subsequent sleep, a phenomenon known as sleep rebound. Disorders such as aging-related sleep changes, obstructive sleep apnea, and certain medications can reduce SWS.

In research and clinical settings, Slow Wave Sleep is assessed via EEG to study sleep depth, architecture, and homeostatic sleep regulation.