MSLT (Multiple Sleep Latency Test)

The MSLT is a test for excessive sleepiness. If left alone in a dark, comfortable, quiet bed long enough, anybody will fall asleep. A well rested person, however, will usually take a significant amount of time (more than 15 to 20 minutes) before succumbing.

After spending the night in the sleep lab and undergoing a polysomnogram to rule out any obvious sleep disturbance, the MSLT patient awakens as usual and goes about their morning routine (breakfast, usual medications, get dressed, etc.). About an hour later, the patient is asked to get back into bed (some of the sensors are left in place or reattached.) The lights are turned out and the patient is instructed to try to nap. A short time later, the patient is asked if they think they fell asleep. Their perception is recorded, as is the brain activity during the test. The patient is then asked to get up and resume normal activities. (Caffeinated coffee and other stimulants are sometimes prohibited during this test.) This procedure is repeated every two hours for four or five trials (depending on the length and depth of the patient’s sleep.) After the final trial, the sensors are removed and the patient is free to leave. The entire procedure takes nine or more hours to complete.

Falling asleep on one or more naps is not unusual, but the sleepier you are, the quicker and more often you will fall asleep. The technologist is also looking at the depth (or stage) of sleep or wake every thirty seconds. Dreaming sleep (REM) during these short trials is unusual, and may signify a disorder such as narcolepsy. (Note: You may experience dreams during sleep, but not be in REM sleep. The brain waves can distinguish the difference.)