Subjects

Forty-six healthy adults (right-handed, 23 male, age range 21–50 years, 18–30 BMI) were recruited in response to study advertisements. They reported habitual nightly sleep durations between 6.5 h–8.5 h, habitual bedtimes between 2200h–0000h, and habitual awakenings between 0600h–0900h; these reports were confirmed objectively using actigraphy. They had no evidence of habitual napping, no sleep disturbances and an absence of extreme morningness or extreme eveningness, assessed by questionnaire61. Subjects were free of acute or chronic medical and psychological conditions, as established by interviews, clinical history, questionnaires, physical examinations and blood (including a fasting blood glucose test) and urine tests. They were nonsmokers and did not participate in shift work, transmeridian travel, or irregular sleep-wake routines in the 60 days prior to the study. Enrolled subjects were monitored at home with actigraphy, sleep-wake diaries, and time-stamped call-ins to assess bedtime and waketime during the week before and after the in-laboratory phase. They were not permitted to use caffeine, alcohol, tobacco and medications (except oral contraceptives) in the week before the laboratory study, as verified by urine screenings. Sleep disorders were excluded by a night of laboratory polysomnography and oximetry measurements.

The study was approved by the Institutional Review Board of the University of Pennsylvania. All subjects provided written informed consent before enrollment, which was in accordance with the Declaration of Helsinki. Subjects were compensated for participating in the study.

Experimental Design

Subjects were screened twice prior to participating in the study; training in a mock MRI scanner occurred during the second screening session. During the study, subjects remained in the laboratory at the Clinical Translational Research Center at the Hospital of the University of Pennsylvania for 5 consecutive days (4 consecutive nights). Subjects arrived at the laboratory in the afternoon and were provided 9 h time-in-bed (TIB) for their baseline sleep night (Figure 6). The first functional magnetic resonance imaging (fMRI) scan session took place the next morning (Baseline [BL] day) from 0700h–1000h. Subjects were then randomized to either a total sleep deprivation (TSD) or control condition. During the second night of the study, sleep-deprived subjects were kept awake and control subjects were allowed 8 h TIB to sleep (Figure 6). The second fMRI scan session took place the next morning (total sleep deprivation [TSD] day or control day 1 [CD1]). Sleep-deprived subjects were then allowed 12 TIB for recovery sleep and control subjects were allowed 8 h TIB to sleep (Figure 6). Each subject was scanned at the same time for each scan to avoid potential time-of-day differences between scans.

Figure 6: Protocol summary. Subjects arrived at the laboratory in the afternoon and were provided 9h time-in-bed (TIB) for their baseline sleep night. The first functional magnetic resonance imaging (fMRI) scan session took place the next morning (Baseline [BL] day) from 0700h-1000h. Subjects were then randomized to either a total sleep deprivation (TSD) or control condition. During the second night of the study, sleep-deprived subjects were kept awake and control subjects were allowed 8 h TIB to sleep. The second fMRI scan session took place the next morning from 0700h-1000h (total sleep deprivation [TSD] day or control day 1 [CD1]). Sleep-deprived subjects were then allowed 12 TIB for recovery sleep and control subjects were allowed 8 h TIB to sleep. Each subject was scanned at the same time for each scan to avoid potential time-of-day differences between scans. Subjects had ad libitum to food/drink during the study. Subjects remained in the laboratory for the duration of the study and were monitored by trained staff at all times to ensure adherence to the protocol. Full size image

Subjects were behaviorally monitored by trained staff continuously to ensure adherence and were not permitted to leave the laboratory during the study. Subjects were ambulatory and were allowed to watch television, read, play video or board games, and perform other sedentary activities between test bouts (which were completed while sitting at the computer) but they were not allowed to exercise. Subjects wore a wrist actigraph throughout the study and wore ambulatory electroencephalography and electrocardiography recording equipment for 24-h intervals. The light levels were held constant at <50 lux during scheduled wakefulness and <1 lux during scheduled sleep periods. Ambient temperature was maintained between 22°–24°C. Food/drink was ad libitum throughout the protocol (caffeine was prohibited).

Measures

Subjects selected their meals/snacks by choosing from various menu options, and by making requests to