Table 1

Brain physiology shifts across sleep states. Human sleep is divided into REM and NREM, with NREM further subdivided into sleep onset (stage 1 sleep), light NREM (stage 2), and SWS (stages 3 and 4). The physiological parameters listed here are characterized by robust state-dependent changes that are thought to be linked to sleep-dependent learning and memory reprocessing. Arrow represents changes in activity relative to waking. See text for explanations.

Physiological correlates of sleep stagesREMStage 2 NREMSWS
Synchronous brain electrical activity4 to 6 Hz12 to 14 Hz0.5 to 4 Hz
Eye movements
Muscle tone
External inputs
Hippocampal-neocortical dialog (HC-NC)NC→HC?HC→NC
Cholinergic modulation (ACh)
Aminergic modulation (NE and 5-HT)
Glucocorticoids (GC)(↓)(↑)
Frontal activation (DLPFC)?
Limbic activation (e.g., anterior cingulate cortex)?
Sensory cortices?