Circadian Rhythms and Time Perception in Healthy Adults During Constant Wakefulness
Trial statusRecruiting
Trial phaseNot applicable
Trial typeInterventional
Biological sexAll
Age23-45
SponsorUniversity of Aarhus
About this trial
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
This trial accepts healthy volunteersQualifiers
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).
Disqualifiers
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.
Trial design
Design model
Single group
Treatments tested in this trial
Constant Routine Wakefulness
BehavioralBehavioral intervention consisting of approximately 36 hours of continuous wakefulness under constant-routine conditions. Environmental factors (light level, temperature, noise) are held as constant as feasible; posture and activity are standardised; and participants receive small, isocaloric snacks at regular intervals. A repeated cognitive and perceptual test battery is administered every two hours to assess time perception, vigilance, mood, and related functions across the circadian cycle.
Treatment groups
30 Participants
are divided into 1 treatment groupGroup A: Constant Routine WakefulnessOther 1 intervention
Trial outcomes
Primary outcomes
1
Time-Interval Production Error Across 36-Hour Constant Routine
Mean absolute error (in seconds) between produced and target time intervals on a time-production task. Participants are asked to produce predefined intervals (e.g., several seconds) without external timing cues. For each 2-hour block, time-production error is averaged across trials; analyses model changes in error across circadian phase and hours awake during the 36-hour constant routine.
Time frame
From the beginning of the constant-routine wakefulness session through 36 hours of continuous wakefulness (time-production task completed every 2 hours).Secondary outcomes
1
Subjective Passage-of-Time Ratings Across 36-Hour Constant Routine
Visual analogue scale ratings of how fast or slow time seems to pass "right now" relative to normal (anchors: much slower than normal - much faster than normal). Ratings are collected once per 2-hour test block. For each block, the passage-of-time score is averaged across trials (if multiple ratings) and modelled as a function of circadian phase and hours awake during the 36-hour constant routine.
Time frame
From the beginning of the constant-routine wakefulness session through 36 hours of continuous wakefulness (passage-of-time ratings completed every 2 hours).2
Psychomotor Vigilance Task (PVT) Median Reaction Time
Median reaction time (milliseconds) on a brief psychomotor vigilance task (PVT) in each 2-hour test block. Participants respond as quickly as possible to visual stimuli presented at random inter-stimulus intervals. For each block, the median reaction time is computed; additional indices such as lapses (responses \> 500 ms) may be derived. Changes in PVT performance across the 36-hour constant routine are analysed in relation to circadian phase and hours awake.
Time frame
From the beginning of the constant-routine wakefulness session through 36 hours of continuous wakefulness (PVT completed every 2 hours).3
Dim Light Melatonin Onset (DLMO) Timing
Circadian phase assessed by the timing of dim light melatonin onset (DLMO) derived from repeated salivary melatonin samples collected under constant-routine conditions. DLMO is defined as the clock time at which salivary melatonin concentration first exceeds a predefined threshold (e.g., 3 pg/mL) and remains above that level. This single phase marker per participant is used to align behavioural and perceptual outcomes to individual circadian phase.
Time frame
During the 36-hour constant-routine wakefulness session (salivary melatonin sampled approximately hourly).Sponsors and contacts
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University of Aarhus
Lead sponsor
Independent Research Fund Denmark
Collaborator
Source ClinicalTrials.gov