The state of sleep (and wakefulness) can be defined based on behavioral as
well as physiological criteria. The former include posture, mobility, response to
stimulation, level of alertness, eyelids, and eye movement (Table I.4.1). The latter
are based on parameters from electroencephalography (EEG), electromiography
(EMG) to assess muscle tone, and electro-oculography, to record eye movements