Free-running sleep: Difference between revisions

{{Short description|Shifting sleep pattern}}

'''Free-running sleep''' is a [[sleep]] pattern characterised by sleep times not [[Entrainment (chronobiology)|''entrained'']] to normal time cues; often referring to a later shifting ''(delay'') on a daily basis. This occurs as the [[circadian rhythm sleep disorder]] [[non-24-hour sleep–wake disorder]],<ref>{{cite web |title=Circadian Rhythm Sleep Disorders |url=https://aasm.org/resources/factsheets/crsd.pdf |website=aasm |access-date=4 July 2024 |archive-date=11 June 2016 |archive-url=https://web.archive.org/web/20160611134934/http://www.aasmnet.org/resources/factsheets/crsd.pdf |url-status=live }}</ref> or when artificially induced in experiments studying [[circadian rhythm]]s and other [[biology|biological]] rhythms within the field of [[chronobiology]].

An individual's or organism's circadian phase can be determined by monitoring an output of the circadian system, the internal [[circadian clock]]. A researcher can precisely determine factors such as daily cycles of [[gene|genetic]] activity, [[body temperature]], [[blood pressure]], [[hormone]] secretion, or [[sleep]] and activity/[[alertness]] patterns.{{Citation needed|date=March 2026}} Alertness can be tracked in humans through performance-based tests or other measures (such as [[somnolence]]),<ref name=":1">{{Cite journal |last=Basner |first=Mathias |last2=Dinges |first2=David F. |last3=Mollicone |first3=Daniel |last4=Ecker |first4=Adrian |last5=Jones |first5=Christopher W. |last6=Hyder |first6=Eric C. |last7=Di Antonio |first7=Adrian |last8=Savelev |first8=Igor |last9=Kan |first9=Kevin |last10=Goel |first10=Namni |last11=Morukov |first11=Boris V. |last12=Sutton |first12=Jeffrey P. |date=2013-02-12 |title=Mars 520-d mission simulation reveals protracted crew hypokinesis and alterations of sleep duration and timing |url=https://pnas.org/doi/full/10.1073/pnas.1212646110 |journal=Proceedings of the National Academy of Sciences |language=en |volume=110 |issue=7 |pages=2635–2640 |doi=10.1073/pnas.1212646110 |issn=0027-8424 |pmc=3574912 |pmid=23297197}}</ref><ref name=":2">{{Cite journal |last=Van Dongen |first=Hans PA |last2=Dinges |first2=David F. |date=2000 |title=Circadian rhythms in fatigue, alertness, and performance |url=https://fatiguemanagersnetwork.org/wp-content/uploads/Van-Dongen-et-al.2000_Circadian-Rhythms-in-Fatigue-Alertness-and-Performance.pdf |url-status=live |journal=Principles and practice of sleep medicine |publisher=W. B. Saunders |volume=20 |pages=391-399 |archive-url=https://web.archive.org/web/20251011125934/https://fatiguemanagersnetwork.org/wp-content/uploads/Van-Dongen-et-al.2000_Circadian-Rhythms-in-Fatigue-Alertness-and-Performance.pdf |archive-date=2025-10-11 |access-date=2026-03-15}}</ref> whereas in animals it can be assessed by observing trends in physical activity (for example, [[Hamster wheel|wheel-running]] in [[rodent]]s).{{Citation needed|date=March 2026|reason=don't think this was properly sourced from the current citations}}

When humans or organisms ''free-run'', experiments can be conducted to determine which signals, known as [[zeitgeber|''zeitgebers'']], are effective in [[Entrainment (chronobiology)|''entrainment'']].<ref name=":0" /> Study subjects are shielded from all time cues, often following [[protocol (natural sciences)|protocols]] such as continuous light, continuous dark, or combined light/dark alternations to which the organism is unable to entrain; for example, a very short (or [[Ultradian rhythm|ultradian]]) period of one hour dark and two hours light.<ref name=":2" /><ref>{{Cite journal |last=Burgess |first=Helen J. |last2=Eastman |first2=Charmane I. |date=2008-08-01 |title=Human Tau in an Ultradian Light-Dark Cycle |url=https://journals.sagepub.com/doi/abs/10.1177/0748730408318592 |journal=Journal of Biological Rhythms |publisher=[[Sage Publishing]] |volume=23 |issue=4 |pages=374-376 |doi=10.1177/0748730408318592 |pmc=3622149 |pmid=18663244 |doi-access=free}}</ref> Other rhythm disruptions may be used, such as providing limited amounts at short intervals to avoid entrainment to average [[Outline of meals|mealtimes]].{{Citation needed|date=March 2026}} These modifications can show the strength and influence of the intrinsic circadian clock.

Researchers can conduct studies to measure entrainment for various organisms and the bounds of circadian cycle lengths. For example, some animals can be entrained to a 22-hour day, but not to a 20-hour day.<ref name=":0" /> Although previous consensus showed human cycles averaging as short as 23.5 hours, or as long as 24.65 hours, several more recent studies determined a tighter average range around 24.18 hours.<ref name=":0">{{cite journal |last=Scheer |first=Frank A.J.L. |author2=Kenneth P. Wright Jr. |author3=Richard E. Kronauer |author4=Charles A. Czeisler |date=2007-08-08 |title=Plasticity of the Intrinsic Period of the Human Circadian Timing System |journal=PLOS ONE |volume=2 |pages=e721 |quote=[E]xposure to moderately bright light (~450 lux; ~1.2 W/m²) for the second or first half of the scheduled wake episode is effective for entraining individuals to the 24.65-h Martian sol and a 23.5-h day length, respectively. |doi=10.1371/journal.pone.0000721 |pmid=17684566 |issue=1 |pmc=1934931 |bibcode=2007PLoSO...2..721S |editor1-last=Nicolelis |editor1-first=Miguel|doi-access=free }}</ref> Observations of free-running and circadian rhythm flexibility are also applicable to situations such as [[Sleep in space|sleep during space travel]], for example, for reduced day lengths required of [[Astronaut|astronauts]] over short periods, or when considering the length of day on a planet such as [[Mars sol|Mars]] (24.65 hours).<ref name=":1" /><ref name=":0" />

 

''Masking'' refers to the effects of non-circadian factors within experiments which could obscure existing patterns or create the appearance of a non-existent rhythm, impacting measurement of timings.<ref name=":2" /> Some examples of masking factors include background noise, ambient temperature, distractions, [[Light effects on circadian rhythm|lighting conditions]], or boredom during the study.<ref name=":2" />

[[Non-24-hour sleep–wake disorder]] ''(Non-24 or N24),'' formerly referred to ''free-running disorder (FRD)'', is a [[circadian rhythm sleep disorder]].<ref name=":3">{{Cite web |last=Pacheco |first=Danielle |date=2018-10-13 |title=Non-24-Hour Sleep Wake Disorder |url=https://www.sleepfoundation.org/non-24-sleep-wake-disorder |access-date=2026-03-15 |website=Sleep Foundation |language=en-US}}</ref> The difference between circadian length and the 24-hour [[24-hour clock|day]], while inadequately synchronised by [[Zeitgeber|''zeitgebers'']], results in free running.<ref>{{Cite journal |last=Quera Salva |first=Maria Antonia |last2=Hartley |first2=Sarah |last3=Léger |first3=Damien |last4=Dauvilliers |first4=Yves A. |date=2017-12-18 |title=Non-24-Hour Sleep–Wake Rhythm Disorder in the Totally Blind: Diagnosis and Management |url=http://journal.frontiersin.org/article/10.3389/fneur.2017.00686/full |journal=Frontiers in Neurology |volume=8 |pages=686 |doi=10.3389/fneur.2017.00686 |issn=1664-2295 |pmc=5741691 |pmid=29326647 |doi-access=free}}</ref> Non-24 affects more than half of people who are totally [[Visual impairment|blind]]<ref>{{cite book |author=Teofilo Lee-Chiong |title=Sleep: a comprehensive handbook |publisher=Wiley-Liss |location=New York |year=2006 |pages=385 |isbn=0-471-68371-X}}</ref> and a small number of sighted individuals.<ref name="AASM">{{Cite journal |last=Sack |first=Robert L. |last2=Auckley |first2=Dennis |last3=Auger |first3=R. Robert |last4=Carskadon |first4=Mary A. |last5=Wright |first5=Kenneth P. |last6=Vitiello |first6=Michael V. |last7=Zhdanova |first7=Irina V. |date=2007-11-01 |title=Circadian Rhythm Sleep Disorders: Part II, Advanced Sleep Phase Disorder, Delayed Sleep Phase Disorder, Free-Running Disorder, and Irregular Sleep-Wake Rhythm |url=https://academic.oup.com/sleep/article-lookup/doi/10.1093/sleep/30.11.1484 |journal=Sleep |language=en |volume=30 |issue=11 |pages=1484–1501 |doi=10.1093/sleep/30.11.1484 |issn=1550-9109 |pmc=2082099 |pmid=18041481}}</ref>  

Among blind people, the cause is the inability to adequately register [[Light effects on circadian rhythm|light cues]], preventing [[Entrainment (chronobiology)|entrainment]].<ref name=":3" /> Many blind people who are able to entrain to a 24-hour light/dark cycle retain functioning [[Retina|retinae]], including operative non-visual light-sensitive cells called [[Intrinsically photosensitive retinal ganglion cell|ipRGCs]].<ref>{{cite journal |author=Tu |title=Physiologic diversity and development of intrinsically photosensitive retinal ganglion cells |journal=Neuron |volume=48 |issue=6 |pages=987–99 |date=December 2005 |pmid=16364902 |doi=10.1016/j.neuron.2005.09.031 |quote=Intrinsically photosensitive retinal ganglion cells (ipRGCs) mediate numerous nonvisual phenomena, including entrainment of the circadian clock to light-dark cycles, pupillary light responsiveness, and light-regulated hormone release. |last2=Zhang |first2=Dongyang |last3=Demas |first3=Jay |display-authors=4 |last4=Slutsky |first4=Elon B. |last5=Provencio |first5=Ignacio |last6=Holy |first6=Timothy E. |last7=Van Gelder |first7=Russell N.|doi-access=free |url=https://www.cell.com/neuron/fulltext/S0896-6273(05)00891-3|first=Daniel C.}}</ref> These [[retinal ganglion cell|ganglion cell]]s, which contain [[melanopsin]], relay signals to the [[circadian clock]] via the [[retinohypothalamic tract]] (branching off from the [[optic nerve]]), which is the pathway from the retina to the [[pineal gland]].<ref>{{cite journal |last=Czeisler |first=Charles A. |author2=Theresa L. Shanahan |author3=Elizabeth B. Klerman |author4=Heinz Martens |author5=Daniel J. Brotman |author6=Jonathan S. Emens |author7=Torsten Klein |author8=Joseph F. Rizzo  |date=5 January 1995 |title=Suppression of melatonin secretion in some blind patients by exposure to bright light |journal=N Engl J Med |volume=332 |issue=1 |pages=6–11 |location=USA |pmid= 7990870 |doi=10.1056/NEJM199501053320102 |quote=[T]he photic pathway used by the circadian system is functionally intact in some blind patients.|doi-access=free }}</ref><ref>{{cite web |url=http://www.endotext.org/neuroendo/neuroendo15/neuroendoframe15.htm |title=Chapter 15. The Pineal Gland and Pineal Tumours |access-date=2008-02-07 |last=Arendt |first=Josephine |date=2006-02-01 |work=Neuroendocrinology, Hypothalamus, and Pituitary |publisher=Endotext.com |pages=an E–book edited by Ashley Grossman (chapter section: Melatonin Synthesis and Metabolism) |quote=Image forming vision (rods and cones) is not required ... for synchronising/phase shifting the circadian clock. |archive-url=https://web.archive.org/web/20080209103150/http://www.endotext.org/neuroendo/neuroendo15/neuroendoframe15.htm |archive-date=2008-02-09 |url-status=dead }}</ref>

Among sighted individuals, non-24 usually first appears during the teens or early twenties. As with [[delayed sleep phase disorder]] (DSPS or DSPD), in the absence of neurological damage due to [[Traumatic brain injury|trauma]] or [[stroke]], cases rarely develop after age 30.<ref name="AASM" /> In a case review, non-24 affected more sighted men than sighted women.<ref name="AASM" /> A quarter of sighted subjects with non-24 also have an associated psychiatric condition.<ref name="AASM" />{{Unreliable medical source|reason=citation within source does not support the claim, only a single case study w/o mention of pop. data|date=March 2026}} A quarter previously showed symptoms of DSPS.<ref name="AASM" />

* [https://web.archive.org/web/20150827010242/http://www.supermemo.com/articles/sleep.htm#Free_running_sleep A collection of articles about sleep (archived)] by Piotr A. Wozniak, May 2012