Also known as a sleep study, this is a multi-parametric test used in the study of sleep and as a diagnostic tool in sleep medicine. The test result is called a polysomnogram, also abbreviated PSG. The name is derived from Greek and Latin roots: the Greek 'poly' for multi-channel (many), the Latin 'somnus' (sleep), and the Greek 'graphein' (to write).

Polysomnography is a comprehensive recording of the biophysiological changes that occur during sleep. It is usually performed at night, when most people sleep, though some labs can accommodate shift workers and people with circadian rhythm sleep disorders and do the test at other times of day. The PSG monitors many body functions including brain (EEG), eye movements (EOG), muscle activity or skeletal muscle activation (EMG) and heart rhythm (ECG) during sleep. 

This is a study used to measure how alert you are during the day. It shows whether or not you are able to stay awake for a defined period of time. This is an indicator of how well you are able to function and remain alert in quiet times of inactivity. 

The test is based on the idea that your ability to stay awake may be more important to know in some cases than how fast you fall asleep. This is the case when the MWT is used to see how well a sleep disorders patient is able to stay awake after starting treatment. It is also used to help judge whether a patient is too tired to drive or perform other daily tasks.

This is a nap study. It is used to see how quickly you fall asleep in quiet situations during the day. The MSLT is the standard way to measure your level of daytime sleepiness. Excessive sleepiness is when you are sleepy at a time and place when you should be awake and alert. It affects about 5% of the general population. 

The study is based on the idea that you should fall asleep in a shorter amount of time as your feeling of sleepiness increases. The MSLT charts your brain waves and heartbeat and records your eye and chin movements. The study also measures how quickly and how often you enter the rapid-eye-movement (REM) stage of sleep. Results of the nap study are routinely used to detect sleep disorders.