A Maintenance of Wakefulness Test (MWT) is similar to an MLST however it tests your ability to stay awake. Often a MWT will follow an overnight night sleep study, but this is not necessary in all cases.  

A MWT is used to evaluate your ability to resist sleep in a quiet dark room without any form of stimulation such as talking to yourself, singing, pinching yourself or tapping your feet.

You will be asked to relax into a semi reclining position and instructed to resist sleep for a 40 minute time period. These tests will occur every two hours, four times during the day. In-between the test periods you will be free to watch TV, read etc. You will not however be able to nap during these free periods, it is important that you remain awake throughout the entire day.

A MWT  is most commonly used for commercial drivers, pilots and people who work around heavy equipment to help determine if they can perform their job safely, especially if they have been diagnosed with a sleep disorder.