Impact of motivation on Multiple Sleep Latency Test and Maintenance of Wakefulness Test measurements.

BACKGROUND: The Multiple Sleep Latency Test (MSLT) and Maintenance of Wakefulness Test (MWT) are standard clinical tests used to measure sleep tendency in clinical populations in which test results may lead to significant life change for patients. Loss of a driving license or drug seeking may provide significant motivation to patients to obtain needed results on these tests. In the current study, the effect of motivation on the ability to fall asleep or stay awake was examined.

METHODS: Twelve subjects spent 3 nights and the following days in the laboratory. On the day following the first laboratory night (screen), subjects performed an MSLT and 40-minute MWT with normal test instructions. On the second or third day, subjects were randomly motivated to appear as sleepy as possible (ie, to fall asleep rapidly) on all of the tests. On the other day, subjects were motivated to be wakeful. The subject with the "best" performance in modifying their sleep latency was paid a bonus as the motivation.

RESULTS: For the MSLT, latency was significantly longer than baseline in the Wakeful condition. For the MWT, latency was significantly shorter in the Sleepy condition, as compared to baseline.

CONCLUSIONS: Subjects have the ability to increase but not decrease sleep latency on the MSLT, and this implies that the MSLT is a better measure of sleepiness rather than alertness. Subjects have the ability to decrease but not increase sleep latency on the MWT, and this implies that the MWT is a better measure of alertness, as compared with sleepiness.