Table 1.

Specific terminology regarding sleep physiology

Slow wave sleep	Another term for stage 3 (N3) of non-REM sleep, also referred to as deep sleep [41]
REM latency	Time between onset of sleep to the first REM stage, changes in REM latency are considered biological markers for a number of sleep-related disorders [42]
Rapid eye movement densities	Frequency of rapid eye movements, can be used as a measure of sleep need, decreases with reduction of sleep duration [43]
Sleep efficiency	Ratio of total sleep time to time spent in bed [44]
Arousals	Central nervous system activation associated with increased sympathetic tone, characterized by an abrupt EEG frequency, which may include alpha and/or theta waves and/or delta waves and/or frequencies greater than 16 Hz lasting at least 3 s [45]
Sleep spindles	Contribute to memory consolidation and neuronal plasticity [46]