Auditory awakening thresholds in sleepy and alert individuals.

Twenty-seven healthy men and women with regular sleep-wake habits (and no habitual napping) participated in a study to determine the relation between auditory awakening thresholds (AAT) and multiple sleep latency test (MSLT) scores. Subjects were free of any sleep complaints and were screened polysomnographically. Nine subjects had a screening MSLT of < or = 5 minutes (sleepy group), and 18 subjects had an MSLT of > or = 10 minutes. Subjects were assigned to three groups: a sleepy group, alert group and an alert sleep-deprived group. Subjects underwent 2 nights of AAT testing with at least 5 days in between each study night. AATs were determined at 0100, 0300, 0500 and 0730 hours. There were a total of 209 available AAT determinations, with a comparable number of trials across the groups. Because 68% of AAT determinations were done out of stage 2 non-rapid eye movement (NREM) sleep, the thrust of the analysis was based on the results of this stage of sleep. The AATs were averaged across the two experimental nights. Trials 1 and 2 (first half of the night) and 3 and 4 (second half of the night) were averaged for each subject. There was no main effect of group on AATs. However, there was a significant main effect of time and a significant group by time interaction. The former indicated an overall decline in AATs across the night. More importantly, the three groups had comparable AAT levels during the first half of the night:. Sleepy and alert-deprived subjects, however, failed to show a decline in AATs, whereas the alert group showed a significant decline in the second half of the night. This differential rate of decline in AATs is suggested to be related to the differences in sleep homeostasis among alert and sleepy individuals.