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In short photoperiods, human sleep is biphasic
Abstract
SUMMARY Results of a photoperiod experiment show that human sleep can be unconsolidated and polyphasic, like the sleep of other animals. When normal individuals were transferred from a conventional 16‐h photoperiod to an experimental 10‐h photo‐period, their sleep episodes expanded and usually divided into two symmetrical bouts, several hours in duration, with a 1–3 h waking interval between them. The durations of nocturnal melatonin secretion and of the nocturnal phase of rising sleepiness (measured in a constant routine protocol) also expanded, indicating that the timing of internal processes that control sleep and melatonin, such as circadian rhythms, had been modified by the change in photoperiod. Previous work suggests that the experimental results could be simulated with dual‐oscillators, entrained separately to dawn and dusk, or with a two‐process model, having a lowered threshold for sleep‐onset during the scotoperiod.
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“Under certain circumstances, the oscillations of E and M can become dissociated from one another. In this situation, coupling forces between the two components continue to operate and tend to draw the components into either of two metastable modes of coupling that are 180° apart17,19.”
From Bipolar mood cycles associated with lunar entrainment of a circadian rhythm (2018) · cites this paper as [19]
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“However, the conditions and significance under which LAN above threshold might affect the duration and phase of melatonin production as well as the overall level of nocturnal melatonin production [50-53] are not well understood, especially in natural environments.”
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“…the industrial revolution and electrification of the modern world was most likely biphasic, with two 3–4 h episodes separated by 1–2 h of wakefulness (Ekirch, 2001, 2005; Fagioli et al., 2001; Wehr, 1992; Wehr et al., 2001), rather than the consolidated 8 h monophasic one characteristic of today.”
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“Related, experimental studies [100,101] have shown bi-phasic nighttime sleep patterns to naturally emerge in contexts where people are deprived from stimuli affecting sleep (e.g., artificial light, modern technology).”
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“Modern humans also exhibit fragmented sleep patterns under short photoperiods (Wehr 1992).”
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“These studies generally report a beneficial impact of napping on alertness and memory consolidation (Hilditch et al., 2017; Mednick et al., 2002); however, night- time sleep following a nap is often lighter (e.g. less slow- wave sleep) as compared with when no naps are taken (Werth et al., 1996).”
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“The presence of such oscillators in humans is hinted at more directly by the overall shape of the melatonin profile, which exhibits two daily peaks in secretion [11], and within the bimodal sleep patterns that emerge in people living under short photoperiods with forced exposure to 14 h of complete darkness [12].”
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“The distinction is quite important, because a requirement for a daily and lengthy period of darkness to maintain optimal circadian health has different implications than a requirement that a person must be asleep during this entire period; it may be normal to experience a wakeful period in the middle of a dark night (…”
Application of Cognitive Behavioral Therapy for Insomnia in the Pediatric Population
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“Human Nature” and the Biology of Everyday Life
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Carskadon, M. A. (2013) · Elsevier eBooks · doi:10.1016/b978-0-12-378610-4.00018-8 · Cited by 4
The Recent History of Seasonal Affective Disorder (SAD)
Overy, C., & Em, T. (2014) · Queen Mary Research Online (Queen Mary University of London) · Cited by 4
Seasonal timing and interindividual differences in shiftwork adaptation
Kim, R., Fang, Y., Lee, M., Kim, D. W., Tang, Z., Sen, S., & Forger, D. B. (2025) · npj Digital Medicine · doi:10.1038/s41746-025-01678-z · Cited by 3
“Substantial evidence from human studies show that photoperiod alone can drive seasonal activity 5,6 .”
Pharmacology of the CNS Peptides
Inoue, S. (1995) · Handbook of experimental pharmacology · doi:10.1007/978-3-642-57836-6_9 · Cited by 3
Groping in the dark: A response to Roger Ekirch
Verhoeven, G. (2020) · Journal of Sleep Research · doi:10.1111/jsr.13177 · Cited by 3
Ekirch, A. R. (2020) · Journal of Sleep Research · doi:10.1111/jsr.13167 · Cited by 3
“(Ekirch, 2005; Warren, 2007; Wehr, 1992).”
Biphasic sleep and human health: A theoretical paradigm for personalized sleep
Sena-Ribeiros, J., & Reis, C. (2025) · Sleep Medicine · doi:10.1016/j.sleep.2025.106743 · Cited by 2
Human Behavior: Sleep in Hunter–Gatherer Societies
Peever, J. H., & Horner, R. L. (2015) · Current Biology · doi:10.1016/j.cub.2015.10.012 · Cited by 2
Haim, A., Kloog, I., Rennert, H. S., & Portnov, B. A. (2011) · Chronobiology International · doi:10.3109/07420528.2011.566090 · Cited by 2
“Most of us are awake for periods during the night, which is normal and healthy (Wehr, 1992), and sometimes one awakens to empty the bladder, and with increasing in frequency with each passing year.”
BackgroundHuman Alertness Optimization with a Three-Process Dynamic Model
Yin, J., Julius, A. A., Wen, J. T.-Y., Wang, Z., He, C., & Kou, L. (2022) · Mathematics · doi:10.3390/math10111916 · Cited by 2
“Then alertness declines steadily in the afternoon and evening until sleep begins, which agrees with daily profiles of cognitive performance and subjective sleepiness [21,22].”
BackgroundMethodTwo oscillatory components detected by forced splitting of the sleep-wake cycle in humans
Hashimoto, S., Endo, T., Honma, S., Yamanaka, Y., & Honma, K. (2023) · American Journal of Physiology-Regulatory, Integrative and Comparative Physiology · doi:10.1152/ajpregu.00094.2023 · Cited by 2
Some Repetitive Activity in Shifts and Sheets
Cole, J. (2016) · Performance Research · doi:10.1080/13528165.2016.1138778 · Cited by 1
“For scientific research into biphasic sleep, see Wehr 1992.”
BackgroundSleep Duration, Melatonin, and Breast Cancer: Compliment and Complement
Erren, T. C. (2006) · Cancer Research · doi:10.1158/0008-5472.can-05-3869 · Cited by 1
Proposed mechanisms between sleep and metabolism
Triay, J. (2014) · Practical Diabetes · doi:10.1002/pdi.1893
Approche sociologique et historique du sommeil, d’hier à aujourd’hui
Birlouez, É. (2016) · Pratiques en nutrition · doi:10.1016/j.pranut.2016.09.003
Kalmbach, K., Booth, V., & Behn, C. D. (2017) · arXiv (Cornell University) · doi:10.48550/arxiv.1710.05494
“ildhood as well as siesta cultures, two-phase nighttime sleep has been observed under short photoperiods and may represent historical sleep patterns that preceded modern articial lighting conditions [49]. Our results also point to a role for REM sleep in the stabilization and de-stabilization of sleep patterns across…”
Kutscher, J., & Leydecker, J. M. (2018) · Springer eBooks · doi:10.1007/978-3-662-56206-2_1
The Effect of Diurnal Phase on Performance Physiology and Immune System
Tormey, P. (2026) · Research Output (Edinburgh Napier University) · doi:10.17869/enu.1023141
Brown, R. F., & Thorsteinsson, E. (2019) · Springer eBooks · doi:10.1007/978-3-030-32545-9_9
Epidemiology of sleep–wake and primary prevention of its disorders
Keller, L. K., Winnebeck, E. C., & Roenneberg, T. (2020) · doi:10.1093/med/9780198713005.003.0111
Spork, P. (2020) · intensiv · doi:10.1055/a-1163-3982
“Schon im Jahr 1992 publizierte der US-amerikanische Schlafforscher Tom Wehr dazu eine viel beachtete Studie [31].”
BackgroundInfluentialHunt, K. D. (2020) · Cambridge University Press eBooks · doi:10.1017/9781316339916.020
Budiawan, W., Tsuzuki, K., & Sakakibara, H. (2021) · IOP Conference Series Earth and Environmental Science · doi:10.1088/1755-1315/896/1/012074
Functions of REMS and Dreaming
(2006) · Kluwer Academic Publishers eBooks · doi:10.1007/0-306-47949-4_13
Metadata
- Authors
- WEHR, T. A.
- Affiliations
- National Institutes of Health (US)
- Corresponding author
- WEHR, THOMAS A.
- ORCID
- WEHR, THOMAS A.
- Venue
- Journal of Sleep Research
- Publisher
- Wiley
- Published
- 1992-06
- Volume
- 1
- Issue
- 2
- Pages
- 103-107
- ISSN
- 0962-1105 (ISSN-L)
- 1365-2869
- OpenAlex
- W1968064632
- Cited by
- 115
- References
- 17
- Citations by year
- 2026: 5 · 2025: 6 · 2024: 6 · 2023: 5 · 2022: 6 · 2021: 7 · 2020: 7 · 2019: 5 · 2018: 10 · 2017: 4 · 2016: 6 · 2015: 8 · 2014: 7 · 2013: 7 · 2012: 1
- FWCI
- 1.31
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Journal of Sleep Research (publishedVersion)
- PubMed (publishedVersion)
- 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 Work-Related Fatigue
- Keywords
- polyphasic sleep, short-day photoperiod, sleep consolidation, circadian rhythm, melatonin secretion, sleepiness, constant routine, two-process model
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