slowwavesömn

Slowwavesömn, commonly called slow-wave sleep (SWS) or deep sleep, is the deepest phase of non-rapid eye movement sleep. It is defined by the appearance of high-amplitude, low-frequency delta waves (approximately 0.5 to 4 Hz) on electroencephalography (EEG). In older sleep staging schemes it comprises stages 3 and 4; modern classifications call this period N3.

During the night, slow-wave sleep is most abundant in the first half of the sleep period and gradually diminishes in later cycles. The amount of SWS declines with age, with older adults showing substantially less slow-wave activity and deeper sleep time.

Physiologically, SWS involves widespread thalamocortical synchronization, resulting in brain states of reduced responsiveness. Autonomic activity slows, respiration stabilizes, and muscle tone remains low but not as complete as in REM sleep. Growth hormone release is commonly associated with SWS, and brain metabolite clearance is enhanced during this phase.

Functions: Slow-wave sleep is implicated in declarative memory consolidation and synaptic homeostasis, a process by which synaptic strength is downscaled to balance learning. It is also linked to glymphatic clearance of metabolic waste from the brain, supporting neural health, and may contribute to immune function and recovery from sleep loss.

Clinical relevance: Disruption or reduction of slow-wave sleep is observed in aging, insomnia, sleep apnea, and certain neurological conditions, and is associated with impaired cognition and mood. SWS is frequently assessed by measuring delta power in EEG or by the proportion of sleep time spent in N3.