deepsleep

Deep sleep, also known as slow-wave sleep or stage N3, is the deepest phase of non-REM sleep. It is characterized by high-amplitude, low-frequency delta waves on electroencephalography, reduced muscle tone, and diminished responsiveness to external stimuli. During deep sleep, heart rate, blood pressure, and breathing reach their lowest levels of the sleep cycle.

Deep sleep occurs mainly during the first half of the night and tends to diminish with age. In healthy young adults, it provides roughly 13-23% of total sleep time, distributed across several episodes that last about 20-40 minutes each. The amount of deep sleep can be reduced by sleep deprivation, alcohol, certain medications, or sleep disorders, with the brain showing compensatory increases in slow-wave activity after deprivation.

Functions of deep sleep include physical restoration, growth hormone release, tissue repair, and immune support. It is associated with the consolidation of declarative memories and is thought to contribute to synaptic homeostasis by downscaling weaker synapses. The brain also engages in glymphatic clearance during deep sleep, aiding the removal of metabolic waste products.

Disruptions to deep sleep are linked to daytime fatigue, impaired cognitive performance, and reduced immune efficiency. Age-related decline in deep sleep is common, but excessive reductions may accompany insomnia, obstructive sleep apnea, and other sleep disorders.

Assessment of deep sleep is typically performed using polysomnography, where stage N3 is identified by delta-dominated EEG activity and a marked reduction in physiological arousal. Monitoring in research and clinical settings may vary in emphasis and methodology.