The Cognitive and Metabolic Effects of Sleep Restriction in Adolescents

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.

Eligibility Criteria:
Inclusion Criteria:

* healthy
* no sleep disorder
* body mass index not greater than 30

Exclusion Criteria:

* smoker
* habitual short sleeper (time in bed during term time of less than 6 hours and no sign of sleep extension of greater than 1 hour on weekends)
* consumption of more than 5 cups of caffeinated beverages a day
* travelling across more than 2 time zones in the month prior to the study protocol
* diagnosed with any psychiatric conditions