The Multiple Sleep Latency Test (MSLT) is used to measure the time it takes from the start of a daytime nap period to the first signs of sleep. The test is based on the idea that the sleepier people are, the faster they will fall asleep.
It can be used to test for narcolepsy, to distinguish between physical tiredness and true excessive daytime sleepiness, or to see if sleep disorder treatments are effective. Its main purpose is to serve as an objective measure of sleepiness.
The test consists of four or five, twenty minute nap opportunities that are scheduled about two hours apart. The test is often done following an overnight sleep study and is performed in the same room as the overnight study. During the test, things such as brain waves, EEG, muscle activity and eye movements are monitored and recorded. Between naps, you are allowed to walk around the sleep lab, or watch TV in the room. The entire test typically takes about 7 hours.