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Sleep Definitions

Sleep is defined behaviorally, electrophysiologically, physiologically, and functionally (see below).

Criteria for the definition of sleep

(Adapted from Moorcroft, 2003; Tobler, 1984; and Zepelin, 1989).
  1. Behavioral
    • typical body posture
    • specific sleeping site
    • behavioral rituals before sleep (e.g., circling, yawning)
    • physical quiescence
    • elevated threshold for arousal and reactivity
    • rapid state reversibility
    • circadian organization of rest-activity cycles
    • hibernation/torpor
  2. Electrophysiological
    • Electroencephalography (EEG)
      • NREM: high voltage slow waves (quiet sleep)
        • spindles in some animals
        • K-complexes in some primates
      • REM: low voltage fast waves (REM, Paradoxical sleep or AS [active sleep])
        • hippocampal theta; PGO waves
    • Electro-oculogram (EOG)
      • NREM: absence of eye movements or slow rolling eye movements
      • REM: rapid eye movements
      • Electromyography (EMG): Progressive loss of muscle tone from Wake to NREM to REM
  3. Physiological
    • REM: instabilities in heart-rate, breathing, body temperature, etc. Other: penile tumescence
    • NREM: reduction in physiologic/metabolic processes; reduction of ~2°C in body temperature
  4. Functional: Compensation of sleep deficit: (homeostatic regulation)
    • enhancement of sleep time
    • intensification of the sleep process (e.g., enhanced EEG power in the Delta range)
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Phylogeny of Sleep | February 13, 2009

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