Sleep architecture

Sleep architecture refers to the cyclical organisation of sleep stages across the night, typically comprising four to six 90-minute ultradian cycles each progressing through N1, N2, N3 (slow-wave sleep), and REM, with N3 dominating early cycles and REM expanding in later ones. Healthy adult sleep contains roughly 15–23% N3 and 20–25% REM, though normative ranges vary with age, sex, and assessment method. Disruptions to architecture—including suppression of N3 by alcohol, fragmentation of REM by sleep apnea, or the age-related decline of slow-wave sleep—have functional consequences for memory consolidation, hormonal secretion, immune regulation, and cardiovascular recovery, making architectural metrics a key target in longevity-oriented sleep assessment.