Effects On The Polysomnogram And Waking Electrocorticogram Of Ad-Libitum Extended-Delayed Sleep

Abstract

The influence arising from an ad-libitum extended-delayed sleep regime on the temporal distribution of REM, slow-wave NREM (stage 2) cycle durations, and waking EEG concurrent with auditory vigilance performance, was evaluated. Subjects were 16 normal healthy young adult males aged 18–24 years who slept 7–8 hr nocturnally. The experiment included an imposed 12–8:00 a.m. control condition and ad-libitum treatment of electrographically recorded laboratory sleep. On the control night the time for retiring was scheduled for 12:00 a.m. and awakening at 8:00 a.m. During the ad libitum treatment the subject was allowed to retire and awaken largely at his own inclination. From a central (C4–A₁) electrocorticogram continuously recorded 1 hr after awakening, during evaluations on auditory vigilance, 1.5-sec epochs of 8–13 Hz alpha rhythm following task-relevant (signal) stimuli were integrated and rectified. The accumulation of slow-wave sleep declined systematically across cycles during both treatments. This attenuation of stages 3–4 during the night in young adults parallels that which occurs with senescence and some clinical pathophysiologic states. Sleep contained in REM cycles across the night was influenced by delayed awakenings from the ad-libitum extended regime. A rise in the length of REM episodes occurred within an interval from 1:00 until 8:30 a.m. During the extended treatment, REM cycle duration attained a maximal level at 8:30 a.m. and declined by 33 min on average at 10:00 a.m. The duration of stage 2 systematically increased across cycles in both treatments. It was hypothesized that the rise in stage 2 may mediate homeostatic functions which allow sleep to be sustained for extended intervals and diurnal naps. There was a statistically significant larger value for integrated waking 8–13 Hz EEG with ad-libitum sleep confined to the initial 15 min of task performance. This elevation of 8–13 Hz EEG alpha rhythm which coincided with delayed (≥ 900 msec) responses-misses was distributed to the 12:37–12:51 p.m. interval during auditory vigilance. These observations indicate that lowered daytime altertness which emanates from delaying an extended interval of sleep is largely confined to variations in wakeful EEG when the requirement for discriminative responses on tasks such as vigilance begin.