Exploration of Neuroscience

State	Stage	% of total sleep¹	Body and brain activity	Mechanism and benefits
NREM	1	N1	2–5	Low-voltage, mixed-frequency brain waves	Transitions from wakefulness and low arousal threshold
2	N2	45–55	Low-voltage, low-frequency brain activity with spindles; reduces muscle tension	Associated with memory consolidation and learning
3	N3	3–8	Increased high-voltage SWS activity	Transition to stage 4; HGH release [41]
4	10–15	Increased high-voltage, SWS; some body movements	HGH release [41]
REM	20–25	Low-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

State

Stage

% of total sleep¹

Body and brain activity

Mechanism and benefits

NREM

2–5

Low-voltage, mixed-frequency brain waves

Transitions from wakefulness and low arousal threshold

45–55

Low-voltage, low-frequency brain activity with spindles; reduces muscle tension

Associated with memory consolidation and learning

3–8

Increased high-voltage SWS activity

Transition to stage 4; HGH release [41]

10–15

Increased high-voltage, SWS; some body movements

HGH release [41]

REM

20–25

Low-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