Can normal subjects be motivated to fall asleep faster?
The Multiple Sleep Latency Test (MSLT) is widely believed to offer an objective, physiological measure of sleepiness. The speed with which a person falls asleep throughout the day is understood to be related systematically to sleep need and circadian phase. This study examined whether normal subjects (n = 14 young female adults) could achieve faster MSLT sleep onsets if they were given the incentive to do so. During week 1 baseline MSLTs were determined over 1 day for all subjects. In week 2 they were randomly assigned to two groups. Control subjects underwent a second MSLT testing day identical to that of week 1, whereas Incentive subjects had an additional financial incentive to sleep. There was a significant reduction in sleep onset latency (indicating increased sleepiness) during the 1500 h trial following the incentive, when subjects also reported a significantly greater increase in sleepiness over the trial. These findings suggest that when coupled with a mid-afternoon increase in sleepiness, increased motivation to sleep can reduce sleep onset latency.