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).
- 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
- 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
- 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
- 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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