Sleep architecture [3841]

StateStage% of total sleep1Body and brain activityMechanism and benefits
NREM1N12–5Low-voltage, mixed-frequency brain wavesTransitions from wakefulness and low arousal threshold
2N245–55Low-voltage, low-frequency brain activity with spindles; reduces muscle tensionAssociated with memory consolidation and learning
3N33–8Increased high-voltage SWS activityTransition to stage 4; HGH release [41]
410–15Increased high-voltage, SWS; some body movementsHGH release [41]
REM20–25Low-voltage, mixed-frequency brain activity; muscle atonia; bursts of REM; irregular HR and breathing (including short breathing apnea)Dreaming, mood regulation, and antidepressant effects are most often associated with REM sleep; memory consolidation in REM is still debated

HGH: human growth hormone; HR: heart rate; NREM: non-rapid eye movement; REM: rapid eye movement; SWS: slow-wave sleep; 1 Estimated for healthy young adults [38]