How the body clock affects time perception during 36 hours awake

CircaTime: Effects of Circadian Rhythms on Time Perception During a 36-Hour Constant Routine in Healthy Adults

This test will see if the internal body clock and staying awake for about 36 hours change how healthy adults experience and estimate time.

Quick facts

• Phase: NA
• Study type: Interventional
• Enrollment: 30 (estimated)
• Ages: 23 Years to 45 Years
• Sex: All
• Sponsor: University of Aarhus (other)
• Locations: 1 site (Aarhus)
• Trial ID: NCT07294781 on ClinicalTrials.gov

What this trial studies

Healthy adult volunteers remain awake for about 36 hours in a controlled laboratory "constant routine" where light, posture, food, and activity are kept steady to minimize external influences. Every two hours participants complete brief tests of sleepiness and mood, a reaction-time task, and multiple measures of time perception such as subjective passage of time and short-interval estimation/production, plus simple decision and color-judgement tasks. Saliva samples are collected repeatedly to measure melatonin as a marker of circadian phase so behavioral changes can be linked to internal clock timing and accumulating sleep pressure. The protocol is designed to separate endogenous circadian effects from environmental changes and map how perception and cognition vary across the circadian cycle.

Who should consider this trial

Good fit: Ideal participants are healthy Danish-speaking adults aged 23–45 with regular sleep schedules, a BMI in a non-extreme range, no recent shift work or major time-zone travel, and willingness to avoid caffeine, nicotine, alcohol, and recreational drugs as required.

Not a fit: People outside the 23–45 age range, non-Danish speakers, those with sleep disorders or significant medical issues, regular night-shift workers, or who cannot comply with the required substance abstinence are unlikely to benefit or be eligible.

Why it matters

Potential benefit: If successful, the findings could improve understanding of how circadian timing and sleep loss alter perception and cognition, which may inform strategies for shift workers and people with sleep problems.

How similar studies have performed: The constant-routine protocol is well established in circadian research and prior work links sleep deprivation and circadian phase to cognitive changes, but detailed effects on multiple measures of time perception are less well charted.

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-routine session.
* For participants who can become pregnant: negative pregnancy test at screening/arrival and agreement to use reliable contraception for the duration of participation.

Exclusion Criteria:

* Any known or suspected major sleep disorder (e.g., insomnia disorder, obstructive sleep apnoea, restless legs syndrome, narcolepsy), based on self-report or prior diagnosis.
* Current or past major psychiatric or neurological disorders (e.g., major depressive disorder, bipolar disorder, psychotic disorders, epilepsy), unless considered mild and stable and explicitly approved by the study physician.
* Chronic medical conditions that could be worsened by prolonged wakefulness or that might confound outcome measures, such as significant cardiovascular disease, uncontrolled hypertension, diabetes mellitus, severe respiratory disease, or other serious systemic illness.
* Regular use of medications or supplements that may affect sleep, circadian rhythms, melatonin secretion, alertness, or mood (e.g., hypnotics, sedative-hypnotics, melatonin, stimulants, certain antidepressants or beta-blockers), unless a safe washout is possible and approved by the study physician.
* High habitual caffeine intake (for example, \>400 mg/day) or nicotine dependence if the participant is unable or unwilling to abstain for the required washout periods.
* Current harmful alcohol use or substance use disorder, or frequent use of recreational drugs.
* Pregnancy or breastfeeding.
* Previous severe adverse reaction to sleep deprivation, extended wakefulness, or similar laboratory protocols.
* Claustrophobia or inability to tolerate prolonged stays in a controlled laboratory environment.
* Any condition or circumstance that, in the judgement of the investigators, would make participation unsafe, interfere with the 36-hour wakefulness protocol, or compromise data quality (e.g., inability to remain awake despite support, strong fear of needles or saliva sampling, or inability to comply with study restrictions).

Where this trial is running

Aarhus

• Aarhus University, Department of Psychology and Behavioural Sciences — Aarhus, Denmark (RECRUITING)

Study contacts

• Study coordinator: Ali Amidi, PhD

Conditions: Sleep Deprivation, Circadian Rhythm, Healthy Volunteers, Time Perception, Circadian rhythms, Constant routine, Extended wakefulness, Sleep loss