Circadian Rhythms and Time Perception in Healthy Adults During Constant Wakefulness
Trial Parameters
Brief Summary
This study examines how the internal body clock (circadian rhythms) influences the way healthy adults experience time, think, and feel when they stay awake for an extended period. Participants will spend about 36 hours in a controlled sleep laboratory while remaining awake the entire time. Light, posture, food intake, and activity are kept as constant as possible (a "constant routine") so that changes over time mainly reflect the body's internal clock and increasing sleepiness, rather than changes in the environment. Every two hours, participants complete a brief test battery that includes ratings of sleepiness and mood, a reaction-time task, and short tasks that assess how fast or slow time seems to pass, how accurately they can estimate time intervals, how they respond to simple decisions, and how they judge colours. Saliva samples are collected repeatedly to measure melatonin, a hormone that indicates circadian phase. By comparing changes in behaviour, perception, and melatonin levels across the 36-hour wake period, the study aims to identify when during the circadian cycle people are most vulnerable to distortions in time perception and reduced alertness. The findings may help improve scheduling of shift work and other activities that require sustained wakefulness.
Eligibility Criteria
Inclusion Criteria: * Age 23 to 45 years. * Able and willing to provide written informed consent. * Fluent in Danish and able to understand study procedures and instructions. * Generally healthy, as assessed by medical history, screening questionnaires, and basic clinical measures (e.g., blood pressure, heart rate). * Self-reported regular sleep-wake schedule for at least 4 weeks prior to the laboratory visit (typically 6.5-9 hours of sleep per night, with usual sleep period between approximately 22:00-01:00 and 06:00-09:00). * Body mass index (BMI) within a non-extreme range (for example, approximately 18.5-30 kg/m²), if required by the study physician. * No regular night work or rotating shift work during the 3 months before participation. * No travel across more than 2 time zones in the 2 months before the constant-routine session. * Willing to abstain from caffeine, nicotine, alcohol, and recreational drugs for the specified washout periods before and during the 36-hour constant-ro