Circadian Clues to Sleep Onset Mechanisms
Abstract
Thermoregulatory processes have long been implicated in initiation of human sleep. A meta-analysis of studies carried out under the controlled conditions of a constant routine protocol followed by nocturnal sleep revealed that heat loss, indirectly measured by the distal-proximal skin temperature gradient, was the best predictor variable for sleep onset latency (compared with core body temperature or its rate of change, heart rate, melatonin onset, and subjective sleepiness ratings). The cognitive signal of "lights out" induced relaxation, with a consequent shift in heat redistribution from the core to the periphery (as measured by an abrupt increase in skin temperatures and a rapid fall in heart rate). These thermoregulatory changes took place before sleep onset: sleep itself had minor further effects. Thus, when the confounding, long-lasting masking effects of lying down are controlled for, circadian thermoregulation initiates sleep, but does not appear to play a major role in its maintenance.
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Thermoregulatory changes preceded by a melatonin rise are robust findings related to psychological cues of relaxation, not time-bound to the evening hours.
“These thermoregulatory changes preceded by a melatonin rise are robust findings related to psychological cues of relaxation (e.g., supine body posture) [53,54] not time-bound to the evening hours, as they are also reported preceding an afternoon nap [31,53,55].”
From Preliminary Results: The Impact of Smartphone Use and Short-Wavelength Light during the Evening on Circadian Rhythm, Sleep and Alertness (2021) · cites this paper as [53]
Changes in thermoregulatory effectors contribute to modification of core body and distal skin temperatures and affect sleep and waking behavior.
“These changes in thermoregulatory effectors in turn contribute to the modification of core body and distal skin temperatures [4–6] and affect sleep and waking behavior [7,8].”
From Human thermal perception and time of day: A review (2021) · cites this paper as [8]
Melatonin enhances heat loss by influencing peripheral vasodilatation, resulting in modification of core body and distal skin temperatures and regulation of sleep.
“Melatonin enhances heat loss by influencing peripheral vasodilatation [54,55], which results in modification of core body and distal skin temperatures and regulation of sleep [7,8].”
From Human thermal perception and time of day: A review (2021) · cites this paper as [8]
Vasodilated distal skin regions, particularly the hands and feet, are the best predictors of sleep initiation.
“Research into human sleep found that vasodilated distal skin regions, particularly the hands and feet, are the best predictors of sleep initiation [8].”
From Human thermal perception and time of day: A review (2021) · cites this paper as [8]
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References 19 · Cited by 213
- Authors
- Kräuchi, K.
- Corresponding author
- Kräuchi, K
- Venue
- Neuropsychopharmacology
- Published
- 2001-11
- Volume
- 25
- Issue
- 5
- Pages
- S92-S96
- ISSN
- 0893-133X (ISSN-L)
- OpenAlex
- W2162337876
- Cited by
- 213
- References
- 19
- Citations by year
- 2026: 17 · 2025: 8 · 2024: 10 · 2023: 8 · 2022: 11 · 2021: 12 · 2020: 8 · 2019: 11 · 2018: 8 · 2017: 13 · 2016: 15 · 2015: 5 · 2014: 5 · 2013: 10 · 2012: 3
- FWCI
- 1.88
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Neuropsychopharmacology (publishedVersion)
- PubMed (publishedVersion)
- Funders
- National Science Foundation
- Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung
- Topics
- Life Sciences › Neuroscience › Endocrine and Autonomic Systems › Circadian rhythm and melatonin
- Life Sciences › Neuroscience › Cognitive Neuroscience › Sleep and Wakefulness Research
- Social Sciences › Psychology › Experimental and Cognitive Psychology › Sleep and related disorders
- Keywords
- sleep onset, heat loss, skin temperature gradient, sleep latency, core body temperature, heart rate, melatonin onset, subjective sleepiness, constant routine, sleep maintenance
- MeSH terms
- Animals, Body Temperature Regulation, Circadian Rhythm, Humans, Melatonin, Skin Temperature, Sleep
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