Measuring the ability to stay awake: role of motivation.

The measurement of daytime sleepiness and alertness is based upon the concepts of physiologic and manifest sleepiness [1]. Physiologic sleepiness is the tendency to fall asleep in the absence of alerting factors and is measured by the multiple sleep latency test (MSLT). Manifest sleepiness changes on a moment-to-moment basis and is determined by factors such as light, noise, motivation, hunger, and recumbency. Manifest sleepiness or the ability of an individual to stay awake under soporific conditions may be more clinically relevant and may be a more important measure for situations in which alertness is warranted, such as driving or operating heavy machinery. The maintenance of wakefulness test (MWT) was developed to measure an individual’s ability to stay awake [2] and is performed with the individual sitting in a room with low ambient light. It is believed that the MWT is a valid test in that the sleep latency on the MWT is shorter for subjects with sleep disorders compared to normal controls and increases with treatment (see an excellent recent review for details [3]. Recent guidelines state that the MWT “may be used to assess an individual’s ability to remain awake when his/her inability to remain awake constitutes a public or personal safety issue” [4]. Given that motivation is considered a determinant of an individual’s ability to stay awake in certain situations, the influence of motivation on the sleep latency measured on the MWT needs to be systematically studied, especially if the test to be used is a test that determines if an individual can remain licensed to drive. Individuals who face loss of license or employment could theoretically manipulate the test, resulting in a normal sleep latency. The study by Shreter et al. [5] published in this issue of Sleep & Breathing sheds light on this issue. The authors investigated a group of patients, the majority with untreated sleepdisordered breathing, who had been referred by the National Council for Driving Safety in Israel for evaluation of daytime sleepiness. All patients were referred knowing that if they “failed” the test their driving license would not renewed. The authors hypothesized that this would be sufficient motivation to maintain wakefulness on the 20-min protocol MWT. Confirming their hypothesis, only 5 out of 54 patients fell asleep on any of the MWT trials. Of the 21 patients with severe untreated obstructive sleep apnea, only one fell asleep during the MWT. The authors conclude that motivation profoundly affects the ability of an individual to stay awake on the MWT. There was one previous study that investigated the influence of motivation on sleep latency in the MWT [6]. In this study, the authors found that motivated normal subjects could decrease their sleep latency (fall asleep faster) on the MWT but were unable to increase their sleep latency (stay awake longer). The authors concluded that the MWT is an excellent choice for measuring daytime alertness as it is minimally affected by a participant’s motivation. There are several methodological differences between the two studies that explain differing results. First, in the study of Bonnet and Arand [6], the subjects served as their own controls. Unfortunately, there is no control group in the Shreter et al. study [5]. The inclusion of patients matched for age, gender, and presence/severity of sleep-disordered breathing but without motivation to “pass the test” (driving license/ employment not at risk) would have increased the reliability of the results. If the control group had an increased rate of falling asleep and a shorter sleep latency on the MWT, then motivation would clearly have been the major reason for the lack of sleep in the at-risk patients. Without the control Sleep Breath (2006) 10:171–172 DOI 10.1007/s11325-006-0071-0