The aim of this study is to examine the neurobehavioural and glucose metabolic responses to two successive cycles of sleep restriction and recovery in adolescents, and to determine the benefits of napping on cognitive performance, alertness, mood and glucose metabolism. Using a split-sleep design, 60 participants, aged 15 to 19 years old, are divided into a nap and a no-nap group. Both groups undergo two cycles of sleep restriction and recovery over a period of 15 days. The no-nap group receives a 6.5-hour sleep opportunity on sleep restriction nights, with no daytime nap opportunity. The nap group receives a 5-hour sleep opportunity on sleep restriction nights, and has a 1.5-hour nap opportunity the following afternoon.
The present study investigates whether a continuous stretch of night time sleep (6.5 hours) will lead to better neurobehavioural outcomes relative to nocturnal sleep restriction (5 hours) and daytime nap (1.5 hours) of the same total duration, and how sleep restriction affects glucose metabolism. The 15-day protocol is conducted in a dormitory on 60 high school students, aged 15 to 19 years old. Participants are assigned to a nap or no-nap group. Both groups start with two 9-hour adaptation and baseline nights, followed by two successive cycles of sleep restriction (5-h time in bed (TIB); 01:00-06:00 or 6.5-h TIB; 00:15-06:45) and recovery (9-h TIB; 23:00-08:00). Following each sleep-restricted night, the nap group receives a 1.5-h nap opportunity, while participants in the no-nap group watch a documentary. Throughout the protocol, sleep-wake patterns are assessed with actigraphy and polysomnography. Sleepiness levels, mood, vigilance, working memory / executive functions, and speed of processing are assessed 3 times daily (10:00, 16:15, and 20:00). Other cognitive functions such as memory and mindfulness levels are investigated through computer-based tasks. Glucose metabolism is measured using oral glucose tolerance tests in the mornings after the second baseline night, the third night of sleep restriction and second recovery night in the first cycle, as well as the last sleep restriction night in the second cycle. All participants stay in air-conditioned, twin-share bedrooms with en-suite bathrooms. Bedroom windows are fitted with blackout panels to ensure participants are not woken up prematurely by sunlight. Earplugs are provided, and participants are allowed to adjust the temperature of their bedrooms to their personal comfort. Three main meals are served each day, with snacks being provided for upon request. Caffeinated drinks, unscheduled sleep, and strenuous physical activities are prohibited. Outside of scheduled sleep, meal, and cognitive testing times, participants spend the majority of their free time in a common room that is illuminated by natural and artificial lighting. They are allowed to read, play non-physically exerting games, watch videos, and interact with research staff and other participants. Participants are under constant supervision by the research staff.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
NONE
Enrollment
59
Looking at the difference between continuous sleep opportunities and split-sleep opportunities.
Duke-NUS Medical School
Singapore, Singapore
Change in sustained attention assessed with the Psychomotor Vigilance Task from morning to afternoon and then evening from baseline days to the first and second cycles of sleep restriction and recovery
Number of attention lapses (\>500ms)
Time frame: 3 times daily (10:00, 16:15, and 20:00) for 15 days
Change in working memory assessed with the 1-back task from morning to afternoon and then evening from baseline days to the first and second cycles of sleep restriction and recovery
Number of correct responses in the 1-back task
Time frame: 3 times daily (10:00, 16:15, and 20:00) for 15 days
Change in executive functions assessed with the 3-back task from morning to afternoon and then evening from baseline days to the first and second cycles of sleep restriction and recovery
Number of correct responses in the 3-back task
Time frame: 3 times daily (10:00, 16:15, and 20:00) for 15 days
Change in the level of subjective sleepiness assessed with the Karolinska Sleepiness Scale from morning to afternoon and then evening from baseline days to the first and second cycles of sleep restriction and recovery
Score on the Karolinska Sleepiness Scale (1-9 points)
Time frame: 3 times daily (10:00, 16:15, and 20:00) for 15 days
Change in positive mood assessed with the Positive and Negative Affect Scale (PANAS) from morning to afternoon and then evening from baseline days to the first and second cycles of sleep restriction and recovery
Total score on the positive subscale of the PANAS
Time frame: 3 times daily (10:00, 16:15, and 20:00) for 15 days
Change in negative mood assessed with the Positive and Negative Affect Scale (PANAS) from morning to afternoon and then evening from baseline days to the first and second cycles of sleep restriction and recovery
Total score on the negative subscale of the PANAS
Time frame: 3 times daily (10:00, 16:15, and 20:00) for 15 days
Change in speed of processing assessed with the Mental Arithmetic Task from morning to afternoon and then evening from baseline days to the first and second cycles of sleep restriction and recovery
Number of correct responses in the task
Time frame: 3 times daily (10:00, 16:15, and 20:00) for 15 days
Change in speed of processing assessed with the Symbol Digit Modalities Task from morning to afternoon and then evening from baseline days to the first and second cycles of sleep restriction and recovery
Number of correct responses in the task
Time frame: 3 times daily (10:00, 16:15, and 20:00) for 15 days
Change in blood glucose level, measured using a blood glucose meter, from baseline following the first period sleep restriction, first period of recovery sleep, and second period of sleep restriction
Score on blood glucose meter
Time frame: Four mornings (after baseline night 2, after sleep restriction night 3 (first sleep restriction period), after recovery night 2 (first recovery period), after sleep restriction night 3 (second sleep restriction period))
Change in meal and snack consumption from baseline following the first period sleep restriction, first period of recovery sleep, and second period of sleep restriction
Amount of meals and snacks consumed, measured on an ad libitum basis
Time frame: Throughout the 15-day protocol
Change in memory performance in picture-word association task over sleep restriction nights and recovery night
Score on picture-word association task
Time frame: 12 times (morning and evening): after sleep restriction night 1, 2, 3, 4 and 5 (sleep restriction period 1) and after recovery night 2 (recovery period 1)
Mind-wandering, assessed using a breath-counting task
Error rate of button presses and percentage of errors that are self-caught
Time frame: Single session, during baseline
Effect of sleep versus wake during delay on the implementation of an intention in the future, where the intention will be encoded either before a 12-hr interval including a night of sleep or a day of wakefulness
Memory score of correctly remembering to perform the intention following the wake or sleep interval
Time frame: Single session during the 15-day protocol, after baseline night 1 or before sleep restriction night 1 (first sleep restriction period)
Effect of sleep versus wake during delay on memory for rewarded pictures, where the pictures will be encoded either before a 12-hr interval including a night of sleep or a day of wakefulness
Memory score of correctly remembered encoded pictures following the wake or sleep interval
Time frame: Single session during the 15-day protocol, after baseline night 1 or before sleep restriction night 1 (first sleep restriction period)
Effect of sleep restriction on learning of novel material (about different animal species) across separate sessions
Memory score on test of learned material
Time frame: Single session during the 15-day protocol, after recovery night 2 (first recovery period)
Effect of sleep restriction on memory of spatial locations
Performance in four mountains task
Time frame: Single session during the 15-day protocol, after sleep restriction night 3 (first sleep restriction period)
Effect of sleep restriction on problem-solving
Number of correctly solved equations in matchstick arithmetic task
Time frame: Single session during the 15-day protocol, after sleep restriction night 5 (first sleep restriction period)
Effect of sleep restriction on picture encoding
Memory score of correctly remembered encoded pictures of non-famous people, landscapes, scenes and objects
Time frame: Single session during the 15-day protocol, after recovery night 2 (second recovery period)
Effect of sleep restriction on effort/temporal discounting
Choice preference (perform a longer duration task for a higher reward, or to take a break for a lower/no reward) in effort/temporal discounting task is measured
Time frame: Three sessions during the 15-day protocol (after baseline night 1, after sleep restriction night 5 (first sleep restriction period) and after recovery night 2 (first recovery period))
Effect of prior knowledge about the position of items in a previously learned hierarchy on learning of the position of novel items in a new hierarchy
Percentage of correct responses on the test
Time frame: Single session, during baseline
Effect of sleep restriction on task switching performance
Difference in reaction time between switch trial and repetition trial in task-switching task
Time frame: Four sessions during the 15-day protocol (after baseline night 1, after sleep restriction night 3 (first sleep restriction period), after recovery night 2 (first recovery period) and after sleep restriction night 3 (second sleep restriction period))
Effect of sleep restriction on attentional bias to threat assessed using visual cues that are coupled either to an aversive sound (threat cue) or a neutral sound (neutral cue)
Correct responses to a target that is presented at the same (valid) or opposite (invalid) location of stimulus
Time frame: Three session during the 15-day protocol (after baseline night 1, after sleep restriction night 5 (first sleep restriction period), after recovery night 1 (first recovery period))
Effect of verbal reward on procedural memory assessed using a finger tapping task
Accuracy of performance on the finger-tapping task
Time frame: Two sessions during the 15-day protocol (before baseline night 1 and after baseline night 1)
Change in total sleep duration at night assessed with polysomnography from baseline nights to the first and second cycles of sleep restriction and recovery
Total duration of nocturnal sleep was determined to establish baseline sleep characteristics (first and second nights) and changes in the first sleep restriction period (third, fifth and seventh night), the first recovery period (eighth night), the second sleep restriction period (tenth and twelfth night), and the second recovery period (13th night).
Time frame: Nocturnal sleep on nights 1 & 2 (baseline), 3, 5 & 7 (first sleep restriction period), 8 (first recovery period), 10 & 12 (second sleep restriction period), & 13 (second recovery period)
Change in N1 sleep duration at night assessed with polysomnography from baseline nights to the first and second cycles of sleep restriction and recovery
Duration of nocturnal N1 sleep was determined to establish baseline sleep characteristics (first and second nights) and changes in the first sleep restriction period (third, fifth and seventh night), the first recovery period (eighth night), the second sleep restriction period (tenth and twelfth night), and the second recovery period (13th night).
Time frame: Nocturnal sleep on nights 1 & 2 (baseline), 3, 5 & 7 (first sleep restriction period), 8 (first recovery period), 10 & 12 (second sleep restriction period), & 13 (second recovery period)
Change in N2 sleep duration at night assessed with polysomnography from baseline nights to the first and second cycles of sleep restriction and recovery
Duration of nocturnal N2 sleep was determined to establish baseline sleep characteristics (first and second nights) and changes in the first sleep restriction period (third, fifth and seventh night), the first recovery period (eighth night), the second sleep restriction period (tenth and twelfth night), and the second recovery period (13th night).
Time frame: Nocturnal sleep on nights 1 & 2 (baseline), 3, 5 & 7 (first sleep restriction period), 8 (first recovery period), 10 & 12 (second sleep restriction period), & 13 (second recovery period)
Change in N3 sleep duration at night assessed with polysomnography from baseline nights to the first and second cycles of sleep restriction and recovery
Duration of nocturnal N3 sleep was determined to establish baseline sleep characteristics (first and second nights) and changes in the first sleep restriction period (third, fifth and seventh night), the first recovery period (eighth night), the second sleep restriction period (tenth and twelfth night), and the second recovery period (13th night).
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Time frame: Nocturnal sleep on nights 1 & 2 (baseline), 3, 5 & 7 (first sleep restriction period), 8 (first recovery period), 10 & 12 (second sleep restriction period), & 13 (second recovery period)
Change in Rapid Eye Movement (REM) sleep duration at night assessed with polysomnography from baseline nights to the first and second cycles of sleep restriction and recovery
Duration of nocturnal REM sleep was determined to establish baseline sleep characteristics (first and second nights) and changes in the first sleep restriction period (third, fifth and seventh night), the first recovery period (eighth night), the second sleep restriction period (tenth and twelfth night), and the second recovery period (13th night).
Time frame: Nocturnal sleep on nights 1 & 2 (baseline), 3, 5 & 7 (first sleep restriction period), 8 (first recovery period), 10 & 12 (second sleep restriction period), & 13 (second recovery period)
Change in total sleep duration during daytime naps assessed with polysomnography from the first to the second sleep restriction period
Total duration of sleep during the selected nap episodes was determined to track changes in this parameter from the first sleep restriction period (third, fifth and seventh day) to the second sleep restriction period (tenth and twelfth day)
Time frame: Afternoon naps on days 4, 6 & 8 (first sleep restriction period), 11 & 13 (second sleep restriction period
Change in N1 sleep duration during daytime naps assessed with polysomnography from the first to the second sleep restriction period
Duration of N1 sleep during the selected nap episodes was determined to track changes in this parameter from the first sleep restriction period (third, fifth and seventh day) to the second sleep restriction period (tenth and twelfth day)
Time frame: Afternoon naps on days 4, 6 & 8 (first sleep restriction period), 11 & 13 (second sleep restriction period
Change in N2 sleep duration during daytime naps assessed with polysomnography from the first to the second sleep restriction period
Duration of N2 sleep during the selected nap episodes was determined to track changes in this parameter from the first sleep restriction period (third, fifth and seventh day) to the second sleep restriction period (tenth and twelfth day)
Time frame: Afternoon naps on days 4, 6 & 8 (first sleep restriction period), 11 & 13 (second sleep restriction period
Change in N3 sleep duration during daytime naps assessed with polysomnography from the first to the second sleep restriction period
Duration of N3 sleep during the selected nap episodes was determined to track changes in this parameter from the first sleep restriction period (third, fifth and seventh day) to the second sleep restriction period (tenth and twelfth day)
Time frame: Afternoon naps on days 4, 6 & 8 (first sleep restriction period), 11 & 13 (second sleep restriction period
Change in REM sleep duration during daytime naps assessed with polysomnography from the first to the second sleep restriction period
Duration of REM sleep during the selected nap episodes was determined to track changes in this parameter from the first sleep restriction period (third, fifth and seventh day) to the second sleep restriction period (tenth and twelfth day)
Time frame: Afternoon naps on days 4, 6 & 8 (first sleep restriction period), 11 & 13 (second sleep restriction period