The Multiple Sleep Latency Test (MSLT) is a sleep disorder diagnostic tool. It is used to measure the time elapsed from the start of a daytime nap period to the first signs of sleep, called sleep latency. The test is based on the idea that the sleepier people are, the faster they will fall asleep. The MSLT is used to test for central disorders of hypersomnolence such as narcolepsy or idiopathic hypersomnia, or to distinguish between physical tiredness and true excessive daytime sleepiness. Its main purpose is to discover how readily a person will fall asleep in a conducive setting, how consistent or variable this is, and whether there are abnormalities in the rapidity of REM sleep onset. This can be used to identify and differentiate between various sleep problems. The test consists of four or five 20-minute nap opportunities set two hours apart, often following an overnight sleep study. During the test, data such as the patient's brain waves, EEG, muscle activity, and eye movements are monitored and recorded. The entire test normally takes about 7 hours during the course of a day. History The Multiple Sleep Latency Test was created in 1977 by sleep pioneers William C. Dement and Mary Carskadon. It developed out of repeating a project done in 1970 by Dr. Dement called the 90-minute day. They informally called the 0–5 minute range the twilight zone due to its indication of extreme physical and mental impairment. Typical procedure Preparation: On the day of the test the patient is asked not to consume any stimulants, such as tea, coffee, colas, and chocolate. Often a formal sleep study has been performed the night before. Sometimes urine screening is done to make sure no substances exist in the subject's body that might interfere with sleep. The patient may be asked to fill out a pre-test questionnaire. Electrodes are attached to the patient's head to record brain waves. Electrodes are attached near the eyes to record eye movement. Electrodes are attached to the chin to detect muscle tone. Heart beat may also be monitored. The patient is asked to perform simple tasks to test that the equipment is working properly. The patient is asked to nap for 20 minutes, and then is awakened. The nap process is repeated every 2 hours for a total of four or five times. The patient must remain awake for the entirety of the 2