Table 1.

Glossary of Commonly-Used Sleep Terms.

Equipment
Polysomnography (PSG)	Sleep-assessment technology based on electrophysiological recordings of brain activity that radiates from the scalp (EEG; electroencephalogram) along with muscle activity (EMG; electromyogram) and eye movement (EOG; electrooculogram). The electrical output is scored and categorised into different stages of sleep/wakefulness to provide information about the pattern and architecture of sleep.
Actigraphy	Sleep-assessment technology that provides an estimate of sleep/wakefulness by monitoring the amount of physical motion. Aided by scoring algorithms, actigraphy provides information about the sleep pattern and diurnal variations of physical activity. Continuous use of actigraphy over successive 24 hour periods can provide reliable information about a person's sleep-wake cycle.
Measure parameters
Sleep onset latency (SOL)	The total amount of time taken to fall asleep.
Wake after sleep onset (WASO)	The total amount of time awake after sleep onset.
Total sleep time (TST)	The total amount of sleep obtained.
Sleep efficiency (SE)	The percentage of time asleep throughout the entire sleep period, which can be calculated by: (TST/total time in bed) x 100%.
Sleep quality (SQ)	A subjective rating of the quality of the sleep obtained and the restful/restored feeling upon waking.
NREM sleep	Non rapid eye movement sleep; one of the two main states of sleep alternating with REM sleep in cycles. NREM sleep is conventionally subdivided into 4 stages (Stages 1, 2, 3 and 4). Stages 1 and 2 are regarded as lighter and Stages 3 and 4 are regarded as deeper stages of sleep. NREM sleep is characterised by synchronous EEG activity and is usually associated with minimal mental and physical activity.
REM sleep	Rapid eye movement sleep; the second main state of sleep. REM sleep is defined by EEG activation, muscle atonia and episodic burst of rapid eye movements. It occurs in 4–6 discrete episodes, making up between 20% to 25% of a normal night of sleep. This state of sleep is associated with dreaming.
Spindle activity	Bursts of EEG activity (12–14 cps) of at least 0.5 seconds that occur in and define Stage 2 sleep.