Many teenagers are familiar with this: on school days, they have to get up early; during the day, they hardly get any light exposure; in the evening, they go to bed late - and are then tired at school the next day! Around the world, teenagers are sleep deprived, with studies suggesting that almost half (\~45%) suffer from inadequate sleep. Previous investigations have shown that people's sleep-wake rhythm is related to the light conditions that they are exposed to during the day and at night. However, little is known about how different light levels in the afternoon can modulate teenagers' sleep and their bodily responses to light in the late evening. Therefore, the investigators aim to study which lighting conditions have a favourable effect on these aspects and how the potentially harmful effects of light at night can be prevented.
Light exposure during adolescence seems to be the critical component of a vicious circle. Due to the maturation of sleep-wake regulatory systems in combination with progressively ill-timed exposure to light and early school start times, teenagers suffer from the accumulation of sleep depth during school days. Therefore, the proposed study investigates whether the physiological and alerting effects of late evening light exposure in adolescents depend on the intensity of light exposure in the preceding afternoon (primary endpoint: evening melatonin concentration). The investigators aim to describe dose-response relationships, where the "dose" is the preceding (real-world applicable) afternoon light intensity (\< 10 lx, \~100 lx, or \>1000 lx EDI, 4-hour duration), and the "responses" are the adolescents' physiological and alerting responses to evening light exposure (\~100 lx melanopic EDI, 4.5-hour duration). By this route, the researchers can explore whether increasing afternoon light exposure is a feasible target for ameliorating the detrimental effects of artificial light at night and promoting healthier sleep-wake regulation during adolescence.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
NONE
Enrollment
27
During the "Dim" light condition, the four-hour afternoon light exposure at the participants' eye level will be dim (\<5 lx melanopic EDI). In the 4.5-hour evening light exposure, this will constitute a light intensity of \~100 lx melanopic EDI at the participants' eye level.
During the "Moderate" light condition, the four-hour afternoon light exposure at the participants' eye level will be dim (\~100 lx melanopic EDI). In the 4.5-hour evening light exposure, this will constitute a light intensity of \~100 lx melanopic EDI at the participants' eye level.
During the "Bright" light condition, the four-hour afternoon light exposure at the participants' eye level will be dim (\>1000 lx melanopic EDI). In the 4.5-hour evening light exposure, this will constitute a light intensity of \~100 lx melanopic EDI at the participants' eye level.
Psychiatric University Clinics (UPK), Centre for Chronobiology
Basel, Canton of Basel-City, Switzerland
Salivary melatonin
Salivary melatonin. Saliva samples (\>1 mL) will be taken from the participants every 30 Minutes using Salivettes. The Salivettes will be centrifuged, the cotton part removed and immediately frozen at -20°C. At a later point, melatonin \[in pg\] will be determined in these samples by double-antibody radioimmunoassay (RIA). To quantify melatonin suppression, the analytic team will calculate the area under the curve (AUC) for each laboratory condition.
Time frame: Through study completion, estimated 1.5 years (within 3 weeks for each participant)
Sleep Onset Latency (PSG-derived)
The investigators will operationalise Sleep Onset Latency according to the American Academy of Sleep Medicine (AASM) Manual for the Scoring of Sleep and Associated Events (time interval from lights out to the first PSG-derived sleep epoch in minutes).
Time frame: Through study completion, estimated 1.5 years (within 3 weeks for each participant)
Slow wave activity (PSG-derived)
The investigators will examine slow-wave activity (SWA; delta power density between 0.5 and 4.5 Hz) during the first sleep cycle. EEG slow-wave activity (SWA) (i.e., delta power density between 0.5 and 4.5 Hz) will be calculated as an indicator of sleep propensity across the night within each non-rapid eye movement NREM part of a sleep cycle.
Time frame: Through study completion, estimated 1.5 years (within 3 weeks for each participant)
Sleep stages (PSG-derived)
The investigators will score the PSG-derived sleep stages and arousals according to the American Academy of Sleep Medicine (AASM) Manual for the Scoring of Sleep and Associated Events.
Time frame: Through study completion, estimated 1.5 years (within 3 weeks for each participant)
Subjective sleepiness
The investigators will assess subjective sleepiness using the single-item 9-point Karolinska Sleepiness Scale (KSS) - a well-validated, highly sensitive subjective Likert-type measurement scale for subjective sleepiness. Scores range from 1 to 9 with higher values on the scale corresponding to higher sleepiness.
Time frame: Through study completion, estimated 1.5 years (within 3 weeks for each participant)
Vigilant attention
Objective alertness will be measured using a modified auditory Psychomotor Vigilance Test (aPVT). After a response, the next tone will be played randomly after 2-10 s. The reaction time data will focus on mean 1/reaction time (mean 1/RT), the most sensitive measure for a slight deviation in sleep pressure. Mean 1/RT will be calculated after the removal of false starts and lapses.
Time frame: Through study completion, estimated 1.5 years (within 3 weeks for each participant)
Melanopsin sensitivity (pupillary light response)
The investigators will measure changes in the pupil area using silent substitution pupillography and examine the differences between melanopsin response amplitude before the afternoon light condition (pre-light treatment) and the melanopsin response amplitude after the afternoon light condition (post-light treatment).
Time frame: Through study completion, estimated 1.5 years (within 3 weeks for each participant)
Skin temperature
Skin temperature will be continuously monitored with six surface temperature thermocouples placed on proximal and distal regions of the body surface. Skin temperatures (distal \& proximal) and the distal-proximal skin temperature gradient (DPG) will be calculated.
Time frame: Through study completion, estimated 1.5 years (within 3 weeks for each participant)
Objective sleepiness 1
The volunteers will perform a Karolinska Drowsiness Test (KDT) three times during scheduled wakefulness. During the KDT, participants fixate on a point on the wall from a one-meter distance for five minutes (eyes open). These sessions will provide EEG data with relatively few artefacts. As the first indicator for objective sleepiness, EEG-derived alpha/theta ratio will be calculated.
Time frame: Through study completion, estimated 1.5 years (within 3 weeks for each participant)
Objective sleepiness 2
The volunteers will perform a Karolinska Drowsiness Test (KDT) three times during scheduled wakefulness. During the KDT, participants fixate on a point on the wall from a one-meter distance for five minutes (eyes open). These sessions will provide EEG data with relatively few artefacts. As the second indicator for objective sleepiness, electro-oculogram-derived (EOG-derived) slow-eye movements will be calculated.
Time frame: Through study completion, estimated 1.5 years (within 3 weeks for each participant)
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