Polysomnography & Sleep Architecture

Sleep is formally scored in 30-second epochs using rules established by the American Academy of Sleep Medicine (AASM). The process requires simultaneous monitoring of brain activity (EEG), eye movement (EOG), and muscle tone (EMG).

NREM Sleep (Non-Rapid Eye Movement)

Stage N1 (Lightest Sleep)

The transition from wakefulness. Characterized by the disappearance of alpha waves and emergence of mixed-frequency, low-amplitude activity. Muscle tone remains relatively high. Usually comprises only 2-5% of total sleep time in healthy adults.

Stage N2 (Light Sleep)

The bulk of human sleep (45-55%). The EEG shows distinct markers: Sleep Spindles (12-14 Hz bursts) and K-complexes (large, slow negative/positive deflections). N2 is crucial for declarative memory consolidation.

Stage N3 (Slow-Wave / Deep Sleep)

The deepest, most restorative stage. Defined clinically when 20% or more of an epoch consists of high-amplitude (>75 μV), low-frequency (0.5-2 Hz) delta waves. Arousal threshold is very high. Essential for:

• Physical restoration and tissue repair.
• Glymphatic clearance (removal of metabolic waste from the brain).
• Release of Human Growth Hormone (HGH).

REM Sleep (Rapid Eye Movement)

Paradoxical sleep. The EEG resembles wakefulness (low-amplitude, mixed-frequency), but muscle tone drops to near paralysis (atonia) to prevent acting out dreams. Intermittent bursts of rapid eye movements occur. REM comprises 20-25% of adult sleep and is critical for emotional regulation and procedural memory.