View source for Hypnagogia

{{short description|State of consciousness leading into sleep}}
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{{about|the psychological state|the musical genre|Hypnagogic pop}}
{{redirect-distinguish|Waking dream|daydreaming}}
'''Hypnagogia''' is the transitional state from [[wakefulness]] to [[sleep]], also defined as the waning state of [[consciousness]] during the [[onset of sleep]]. Its corresponding state is ''[[hypnopompia]]'' {{ndash}} sleep to wakefulness. Mental phenomena that may occur during this "threshold consciousness" include [[hallucination]]s, [[lucid dream]]ing, and [[sleep paralysis]].

== Etymology ==
In 1848, [[Louis Ferdinand Alfred Maury|Alfred Maury]] introduced the term "hypnagogic" from the Greek words ύπνος ("hypnos"), meaning "sleep", and αγωγός ("agōgos"), meaning "conductor" or "leader". Later, in 1904, [[Frederic William Henry Myers|Frederic Myers]] coined the term "hypnopompic," with its word-ending originating from the Greek word "pompos," meaning "sender."<ref>{{Cite journal |last1=Ghibellini |first1=Romain |last2=Meier |first2=Beat |date=February 2023 |title=The hypnagogic state: A brief update |journal=Journal of Sleep Research |volume=32 |issue=1 |article-number=e13719 |doi=10.1111/jsr.13719 |issn=0962-1105 |pmid=36017720|pmc=10078162 }}</ref>

==Definitions==
The word ''hypnagogia'' is sometimes used in a restricted [[word sense|sense]] to refer to the onset of sleep, and contrasted with ''[[hypnopompia]]'', [[Frederic William Henry Myers|Frederic Myers]]'s term for waking up.<ref>{{cite book |title=Human Personality and Its Survival of Bodily Death |url=https://archive.org/details/in.ernet.dli.2015.31563 |first=Frederic |last=Myers |publisher=London: Longmans |year= 1903}}</ref> However, ''hypnagogia'' is also regularly employed in a more general sense that covers both falling asleep and waking up. Indeed, it is not always possible in practice to assign a particular episode of any given [[phenomenon (science)|phenomenon]] to one or the other, given that the same kinds of [[subjective experience|experience]] may occur in both as people drift in and out of sleep.

Other terms for hypnagogia, in one or both senses, that have been proposed include "presomnal" or "anthypnic sensations", "visions of half-sleep", "oneiragogic images" and "phantasmata",<ref name="mavromatis">{{harvp|Mavromatis|1987|p=1}}</ref> "the borderland of sleep", "praedormitium",<ref name="mavromatis4"/> "borderland state", "half-dream state", "pre-dream condition",<ref>Lachman, Gary (2002). [https://web.archive.org/web/20071013131259/http://forteantimes.com/features/articles/227/hypnagogia.html 'Hypnagogia']. ''Fortean Times''.</ref> "sleep onset dreams",<ref name="transcript">Stickgold, R., interviewed 30 October 2000 by [[Norman Swan]] for ''[[The Health Report]]'' on Australia's [[Radio National]] ([https://web.archive.org/web/20001109180400/http://abc.net.au/rn/talks/8.30/helthrpt/stories/s206232.htm transcript]). Retrieved 3 July 2008.</ref> "dreamlets",<ref name="Schachter">{{cite journal | author = Schacter D.L. | year = 1976 | title = The hypnagogic state: A critical review of the literature | journal = Psychological Bulletin | volume = 83 | issue = 3 | pages = 452–481 | doi=10.1037/0033-2909.83.3.452| pmid = 778884 | s2cid = 1151874 }}</ref> and "wakefulness-sleep transition" (WST).<ref name="sciencedirect.com">{{cite journal|last1=Bódizs|first1=Róbert|last2=Sverteczki|first2=Melinda|last3=Mészáros|first3=Eszter|title=Wakefulness–sleep transition: Emerging electroencephalographic similarities with the rapid eye movement phase|journal=Brain Research Bulletin|volume=76|issue=1–2|year=2008|pages=85–89|issn=0361-9230|doi=10.1016/j.brainresbull.2007.11.013|pmid=18395615|s2cid=6066430}}</ref>

Threshold consciousness (commonly called "half-asleep" or "half-awake", or "mind awake body asleep") describes the same mental state of someone who is moving towards sleep or wakefulness but has not yet completed the transition. Such transitions are usually brief but can be extended by sleep disturbance or deliberate induction, for example during [[meditation]].{{Citation needed|date=February 2011}}

==Signs and symptoms==
Transition to and from sleep may be attended by a wide variety of [[sense|sensory]] experiences. These can occur in any modality, individually or combined, and range from the vague and barely perceptible to vivid [[hallucination]]s.<ref>{{harvp|Mavromatis|1987|p=14}}</ref>

===Sights===
Among the more commonly reported,<ref name="Hori"/><ref name="Germaine, A. 1997 p. 243"/> and more thoroughly researched, sensory features of hypnagogia are [[phosphenes]] which can manifest as seemingly random speckles, lines or geometrical patterns, including [[form constants]], or as [[figurative art|figurative]] (representational) [[mental image|images]]. They may be [[monochromatic]] or richly coloured, still or moving, flat or three-dimensional (offering an impression of [[perspective (visual)|perspective]]). Imagery representing movement through tunnels of light is also reported. Individual images are typically fleeting and given to very rapid changes. They are said to differ from dreams proper in that hypnagogic imagery is usually static and lacking in narrative content,<ref name="mp.uni-tuebingen.de"/> although others understand the state rather as a gradual transition from hypnagogia to fragmentary dreams,<ref>{{cite journal | vauthors = Lehmann D, Grass P, Meier B | year = 1995 | title = Spontaneous conscious covert cognition states and brain electric spectral states in canonical correlations | journal = International Journal of Psychophysiology | volume = 19 | issue = 1 | pages = 41–52 | doi=10.1016/0167-8760(94)00072-m| pmid = 7790288 }}</ref> i.e., from simple ''[[eigengrau|Eigenlicht]]'' to whole [[imagination|imagined]] scenes. Descriptions of exceptionally vivid and elaborate hypnagogic visuals can be found in the work of [[Marie-Jean-Léon, Marquis d'Hervey de Saint Denys|Marie-Jean-Léon, {{wbr}}Marquis {{wbr}}d'Hervey {{wbr}}de {{wbr}}Saint {{wbr}}Denys]].

===''Tetris'' effect===
People who have spent a long time at some repetitive activity before sleep, in particular one that is new to them, may find that it dominates their imagery as they grow [[somnolence|drowsy]], a tendency dubbed the [[Tetris effect|'' Tetris'' effect]]. This effect has even been observed in [[amnesia]]cs who otherwise have no [[memory]] of the original activity.<ref>{{cite journal | vauthors = Stickgold R, Malia A, Maguire D, Roddenberry D, O'Connor M | year = 2000 | title = Replaying the game: Hypnagogic images in normals and amnesics | journal = Science | volume = 290 | issue = 5490| pages = 350–3 | doi=10.1126/science.290.5490.350 | pmid=11030656| bibcode = 2000Sci...290..350S }}</ref> When the activity involves moving objects, as in the video game ''[[Tetris]]'', the corresponding hypnagogic images tend to be perceived as moving. The ''Tetris'' effect is not confined to visual imagery but can manifest in other modalities. For example, [[Robert Stickgold]] recounts having experienced the touch of rocks while falling asleep after mountain climbing.<ref name=" transcript"/> This can also occur to people who have travelled on a small boat in rough seas or have been swimming through waves, shortly before going to bed, and they feel the waves as they drift to sleep, or people who have spent the day skiing who continue to "feel snow" under their feet. People who have spent considerable time jumping on a trampoline will find that they can feel the up-and-down motion before they go to sleep. New employees working stressful and demanding jobs often report feeling the experience of performing work-related tasks in this period before sleep.{{cn|date=January 2024}}

===Sounds===
Hypnagogic hallucinations are often auditory or have an auditory component. Like the visuals, hypnagogic sounds vary in intensity from faint impressions to loud noises, like knocking and crashes and bangs ([[exploding head syndrome]]). People may imagine their own name called, crumpling bags, white noise, or a doorbell ringing. Snatches of imagined [[spoken language|speech]] are common. While typically [[nonsensical]] and fragmented, these speech events can occasionally strike the individual as apt comments on—or summations of—their [[thought]]s at the time. They often contain [[word play]], [[neologism]]s and made-up names. Hypnagogic speech may manifest as the subject's own "[[internal monologue|inner voice]]", or as the voices of others: familiar people or strangers. More rarely, poetry or music is heard.<ref name="mavromatis81">{{harvp|Mavromatis|1987|p=81}}</ref>

===Other sensations===
[[Gustatory]], [[olfactory]] and [[thermoception|thermal]] sensations in hypnagogia have all been reported, as well as [[Touch|tactile]] sensations (including those kinds classed as [[paresthesia]] or [[formication]]). Sometimes there is [[synesthesia]]; many people report seeing a flash of light or some other visual image in response to a real sound. [[Proprioceptive]] effects may be noticed, with numbness and changes in perceived body size and proportions,<ref name="mavromatis81"/> feelings of floating or bobbing as if their bed were a boat, and [[out-of-body experience]]s.<ref>{{cite book |title=Out of Body Experiences |first=Robert |last=Petersen |publisher=Hampton Roads Publishing Company, Inc. |year=1997 |isbn=1-57174-057-0 |url=https://archive.org/details/outofbodyexperie00pete }}</ref> Perhaps the most common experience of this kind is the falling sensation, and associated [[hypnic jerk]], encountered by many people, at least occasionally, while drifting off to sleep.<ref>{{cite journal | author = Oswald Ian | year = 1959 | title = Sudden bodily jerks on falling asleep | journal = Brain | volume = 82 | issue = 1| pages = 92–103 | doi=10.1093/brain/82.1.92| pmid = 13651496 }}</ref>

===Cognitive and affective phenomena===
[[Thought]] processes on the edge of sleep tend to differ radically from those of ordinary wakefulness. For example, something that one agreed with while in a state of hypnagogia may seem completely ridiculous while in a waking state. Hypnagogia may involve a "loosening of [[Human ego|ego]] boundaries&nbsp;... openness, sensitivity, internalization-subjectification of the physical and mental environment ([[empathy]]) and diffuse-absorbed [[attention]]."<ref>{{harvp|Mavromatis|1987|p=82}}</ref> Hypnagogic [[cognition]], in comparison with that of normal, alert wakefulness, is characterized by heightened [[suggestibility]],<ref>Ellis, Havelock (1897). 'A note on hypnagogic paramnesia'. ''Mind'', New Series, Vol. 6:22, 283–287.</ref> illogic and a fluid association of [[idea]]s. Subjects are more receptive in the hypnagogic state to [[suggestion]] from an experimenter than at other times, and readily incorporate external [[stimulus (physiology)|stimuli]] into hypnagogic trains of thought and subsequent dreams. This receptivity has a [[physiological]] parallel; [[EEG]] readings show elevated responsiveness to sound around the onset of sleep.<ref>{{harvp|Mavromatis|1987|pp=53–54}}</ref>

[[Herbert Silberer]] described a process he called ''autosymbolism'', whereby hypnagogic hallucinations seem to represent, without [[psychological repression|repression]] or censorship, whatever one is thinking at the time, turning abstract [[idea]]s into a concrete [[mental image|image]], which may be perceived as an apt and succinct representation thereof.<ref>Silberer, Herbert (1909). 'Bericht Ueber eine Methode, gewisse symbolische Hallucinations-Erscheinungen hervorzurufen und zu beobachten'. ''Jahrbuch für psychoanalytische Forschungen'' 1:2, pp. 513–525; Eng. Transl. by Rapaport D., 'Report on a method of eliciting and observing certain symbolic hallucination phenomena', in Rapaport's ''Organization and pathology of thought'', pp. 195–207 (Columbia Univ. Press, New York 1951.).</ref>

The hypnagogic state can provide [[insight]] into a [[Problem solving|problem]], the best-known example being [[August Kekulé]]'s realization that the structure of [[benzene]] was a closed ring while half-asleep in front of a fire and seeing molecules forming into snakes, one of which formed an [[ourobouros]].<ref>{{cite journal |title=Creative Cognitive Processes in Kekulé's Discovery of the Structure of the Benzene Molecule |first=Albert |last=Rothenberg |journal=The American Journal of Psychology |pages=419–438 |jstor=1422898 |publisher=University of Illinois Press |volume=108 |number=3 |date=Autumn 1995 |doi=10.2307/1422898}}</ref> Many other artists, writers, scientists and inventors – including [[Ludwig van Beethoven|Beethoven]], [[Richard Wagner]], [[Walter Scott]], [[Salvador Dalí]], [[Thomas Edison]], [[Nikola Tesla]] and [[Isaac Newton]] – have credited hypnagogia and related states with enhancing their creativity.<ref>{{Citation|last=Krippner|first=Stanley|title=Altered and Transitional States|date=2020|url=https://linkinghub.elsevier.com/retrieve/pii/B9780128093245236201|encyclopedia=Encyclopedia of Creativity|pages=29–36|publisher=Elsevier|language=en|doi=10.1016/b978-0-12-809324-5.23620-1|isbn=978-0-12-815615-5|s2cid=242611424|access-date=2021-12-12|url-access=subscription}}</ref> A 2001 study by Harvard psychologist [[Deirdre Barrett]] found that, while problems can also be solved in full-blown dreams from later stages of sleep, hypnagogia was especially likely to solve problems which benefit from hallucinatory images being critically examined while still before the eyes.<ref>{{Cite book|last=Barrett|first=Deirdre|url=https://books.google.com/books?id=VKZWAAAAYAAJ|title=The Committee of Sleep: How Artists, Scientists, and Athletes Use Dreams for Creative Problem-solving-- and how You Can, Too|date=2001|publisher=Crown Publishers|isbn=978-0-8129-3241-6|language=en}}</ref>

A feature that hypnagogia shares with other stages of sleep is [[amnesia]]. But this is a selective forgetfulness, affecting the [[hippocampal]] memory system, which is responsible for [[episodic memory|episodic]] or [[autobiographical memory]], rather than the [[neocortical]] memory system, responsible for [[semantic memory]].<ref name="transcript"/> It has been suggested that hypnagogia and [[REM sleep]] help in the consolidation of semantic memory,<ref>{{cite journal | last=Stickgold | first=Robert | title=Sleep: off-line memory reprocessing | journal=Trends in Cognitive Sciences | publisher=Elsevier BV | volume=2 | issue=12 | date=1998-12-01 | issn=1364-6613 | doi=10.1016/s1364-6613(98)01258-3 | pages=484–492| pmid=21227299 | s2cid=37085634 }}</ref> but the evidence for this has been disputed.<ref>{{cite journal | author = Vertes Robert E., Kathleen Eastman E. | year = 2000 | title = The case against memory consolidation in REM sleep | journal = Behavioral and Brain Sciences | volume = 23 | issue = 6 | pages = 867–76 | doi=10.1017/s0140525x00004003| pmid = 11515146 | s2cid = 145678531 }}</ref> In particular, suppression of REM sleep due to [[antidepressant]]s and [[lesion]]s to the [[brainstem]] has not been found to produce detrimental effects on cognition.<ref>{{cite journal | author = Vertes R | year = 2004 | title = Memory Consolidation in SleepDream or Reality | journal = Neuron | volume = 44 | issue = 1| pages = 135–48 | doi=10.1016/j.neuron.2004.08.034 | pmid=15450166| doi-access = free }}</ref>

Hypnagogic phenomena may be interpreted as [[hallucination|visions]], [[prophecies]], [[premonitions]], [[apparitional experience|apparitions]] and inspiration ([[artistic inspiration|artistic]] or [[divine inspiration|divine]]), depending on the experiencers' beliefs and those of their culture.

==Physiology==
Physiological studies have tended to concentrate on hypnagogia in the strict sense of spontaneous sleep onset experiences. Such experiences are associated especially with stage 1 of [[NREM sleep]],<ref>Rechtschaffen, A., & Kales, A. (1968). ''A manual of standardized terminology, techniques and scoring system for sleep stages of human subjects''. Washington, DC: Public Health Service, U.S. Government Printing.</ref> but may also occur with pre-sleep [[alpha wave]]s.<ref>{{cite journal | author = Foulkes D., Vogel G. | year = 1965 | title = Mental activity at sleep onset | journal = Journal of Abnormal Psychology | volume = 70 | issue = 4 | pages = 231–43 | doi=10.1037/h0022217| pmid = 14341704 }}</ref><ref>{{cite journal | author = Foulkes D., Schmidt M. | year = 1983 | title = Temporal sequence and unit composition in dream reports from different stages of sleep | journal = Sleep | volume = 6 | issue = 3 | pages = 265–80 | doi = 10.1093/sleep/6.3.265 | pmid = 6622882 | doi-access = free }}</ref> Davis et al. found short flashes of dreamlike imagery at the onset of sleep to correlate with drop-offs in alpha [[EEG]] activity.<ref name="Davis, H. 1937"/> Hori et al. regard sleep onset hypnagogia as a state distinct from both wakefulness and sleep with unique [[electrophysiological]], [[behavior]]al and [[subjectivity|subjective]] characteristics,<ref name="Hori"/><ref name="mp.uni-tuebingen.de"/> while Germaine et al. have demonstrated a resemblance between the EEG [[spectral density|power spectra]] of spontaneously occurring hypnagogic images, on the one hand, and those of both [[REM sleep]] and relaxed wakefulness, on the other.<ref>{{cite journal | vauthors = Nielsen T, Germain A, Ouellet L | year = 1995 | title = Atonia-signalled hypnagogic imagery: Comparative EEG mapping of sleep onset transitions, REM sleep, and wakefulness | journal = Sleep Research | volume = 24 | page = 133 }}</ref>

To identify more precisely the nature of the EEG state which accompanies imagery in the transition from wakefulness to sleep, Hori et al. proposed a scheme of 9 EEG stages defined by varying proportions of [[alpha wave|alpha]] (stages 1–3), suppressed waves of less than 20μV (stage 4), [[theta wave|theta]] ripples (stage 5), proportions of [[sawtooth wave|sawtooth]] waves (stages 6–7), and presence of [[sleep spindle|spindles]] (stages 8–9).<ref name="Hori">Hori, T., Hayashi, M., & Morikawa, T. (1993). Topographical EEG changes and hypnagogic experience. In: Ogilvie, R.D., & Harsh, J.R. (Eds.) ''Sleep Onset: Normal and Abnormal Processes'', pp. 237–253.</ref> Germaine and Nielsen found spontaneous hypnagogic imagery to occur mainly during Hori sleep onset stages 4 (EEG flattening) and 5 (theta ripples).<ref name="Germaine, A. 1997 p. 243">{{cite journal | author = Germaine A., Nielsen T.A. | year = 1997 | title = Distribution of spontaneous hypnagogic images across Hori's EEG stages of sleep onset | journal = Sleep Research | volume = 26 | page = 243 }}</ref>

The "covert-rapid-eye-movement" hypothesis proposes that hidden elements of [[REM sleep]] emerge during the wakefulness-sleep transition stage.<ref name="BódizsSverteczki2005">{{cite journal|last1=Bódizs|first1=Róbert|last2=Sverteczki|first2=Melinda|last3=Lázár|first3=Alpár Sándor|last4=Halász|first4=Péter|title=Human parahippocampal activity: non-REM and REM elements in wake–sleep transition|journal=Brain Research Bulletin|volume=65|issue=2|year=2005|pages=169–176|issn=0361-9230|doi=10.1016/j.brainresbull.2005.01.002|pmid=15763184|s2cid=20787494|doi-access=free}}</ref>
Support for this comes from Bódicz et al., who notes a greater similarity between WST (wakefulness-sleep transition) EEG and REM sleep EEG than between the former and stage 2 sleep.<ref name="sciencedirect.com"/>

[[Respiratory]] pattern changes have also been noted in the hypnagogic state, in addition to a lowered rate of [[frontalis muscle]] activity.<ref name="Schachter"/>

===Daydreaming and waking reveries===
[[Microsleep]] (short episodes of immediate sleep onset) may intrude into wakefulness at any time in the wakefulness-sleep cycle, due to [[sleep deprivation]] and other conditions,<ref>Oswald, I. (1962). ''Sleeping and waking: Physiology and psychology''. Amsterdam: Elsevier.</ref> resulting in impaired cognition and even amnesia.<ref name="mp.uni-tuebingen.de"/>

In his book, ''[[Zen and the Brain]]'', [[James H. Austin]] cites speculation that regular meditation develops a specialized skill of "freezing the hypnagogic process at later and later stages" of the onset of sleep, initially in the alpha wave stage and later in theta.<ref>Austin, James H.(1999) ''Zen and the Brain: Toward an Understanding of Meditation and Consciousness''. First MIT Press paperback edition, 1999. MIT Press. {{ISBN|0-262-51109-6}}, p. 92.</ref>

==History==
Early references to hypnagogia can be found in the writings of [[Aristotle]], [[Iamblichus]], [[Gerolamo Cardano|Cardano]], [[Simon Forman]], and [[Swedenborg]].<ref>{{harvp|Mavromatis|1987|pp=3–4}}</ref> [[Romanticism]] brought a renewed interest in the subjective experience of the edges of sleep.<ref>Pfotenhauer, Helmut & Schneider, Sabine (2006). ''Nicht völlig wachen und nicht ganz ein Traum: Die Halfschlafbilder in der Literatur''. Verlag Königshausen & Neumann. {{ISBN|3-8260-3274-8}}.</ref> In more recent centuries, many authors have referred to the state; [[Edgar Allan Poe]], for example, wrote of the "fancies" he experienced "only when I am on the brink of sleep, with the consciousness that I am so."<ref name="mavromatis4">{{harvp|Mavromatis|1987|p=4}}</ref>

In Charles Dickens's ''[[Oliver Twist]]'' there is a pair of episodes, one that portrays the title character experiencing a hypnopompic state, which precedes the following episode, which describes him in a hypnagogic state:
 
<blockquote>There is a kind of sleep that steals upon us sometimes, which, while it holds the body prisoner, does not free the mind from a sense of things about it, and enable it to ramble at its pleasure. … It is an undoubted fact, that although our senses of touch and sight be for the time dead, yet our sleeping thoughts, and the visionary scenes that pass before us, will be influenced and materially influenced, by the mere silent presence of some external object; which may not have been near us when we closed our eyes: and of whose vicinity we have had no waking consciousness."<ref>[http://www.jstor.org/stable/45292632] Edgecomb, Rodney Stenning. "The Oneiric Vision of "Oliver Twist". ''Dickens Quarterly''. Vol. 31, No. 2, June 2014. p. 98-102</ref><ref>Charles Dickens, ''Oliver Twist'', Chapter 34</ref></blockquote>

Serious scientific inquiry began in the 19th century with [[Johannes Peter Müller]], [[Jules Baillarger]], and Alfred Maury, and continued into the 20th century with Leroy.<ref>Leroy, E.B. (1933). ''Les visions du demi-sommeil''. Paris: Alcan.</ref>

[[Francis Galton]] in his ''The Visions of Sane Persons'' (1881), wrote:

: [B]efore I thought of carefully trying, I should have emphatically declared that my field of view in the dark was essentially of a uniform black, subject to an occasional light-purple cloudiness and other small variations. Now, however, after habituating myself to examine it with the same sort of strain that one tries to decipher a sign-post in the dark, I have found out that this is by no means the case, but that a kaleidoscopic change of patterns and forms is continually going on, but they are too fugitive and elaborate for me to draw with any approach to truth.

[[Maria Manaseina|Maria Mikhaĭlovna Manaseina]] wrote "that for these phenomena to attract attention a certain power of observation is required; that is why they are chiefly found in intelligent persons." Manaseina also noted that children are more likely to take interest in them: "[M]any children are accustomed to press their heads into the pillow and adopt an attitude of expectant attention towards the visions that then begin to form…"<ref>Maria Mikhaĭlovna Manaseina ''Sleep, its Physiology, Pathology, Hygiene, and Psychology'' (1897)</ref>

[[Havelock Ellis]] later recalled such a childhood interest in these visions:

: I should myself be inclined to deny that I had ever had any such visionary faculty [for hypnagogic hallucination] if it were not that I can recall one occasion of its presence, at about the age of seven, when sleeping with a cousin of the same age; we amused ourselves by burying our heads in the pillows and watching a connected series of pictures which we were both alike able to see, each announcing any change in the picture as soon as it took place.<ref>Havelock Ellis ''The World of Dreams'' (1916)</ref>

The advent of [[electroencephalography]] (EEG) supplemented the introspective methods of these early researchers with physiological data. The search for neural correlates for hypnagogic imagery began with Davis ''et al.'' in the 1930s,<ref name="Davis, H. 1937">{{cite journal | vauthors = Davis H, Davis PA, Loomis AL, Harvey EN, Hobart G | year = 1937 | title = Changes in human brain potentials during the onset of sleep | journal = Science | volume = 86 | issue = 2237 | pages = 448–50 | doi=10.1126/science.86.2237.448| pmid = 17838964 | bibcode = 1937Sci....86..448D }}</ref> and continues with increasing sophistication. While the dominance of the [[behaviorist]] paradigm led to a decline in research, especially in the English speaking world, the later twentieth century has seen a revival, with investigations of hypnagogia and related [[altered states of consciousness]] playing an important role in the emerging multidisciplinary study of [[consciousness]].<ref name="mp.uni-tuebingen.de">{{cite journal|last1=Vaitl|first1=Dieter|last2=Birbaumer|first2=Niels|last3=Gruzelier|first3=John|last4=Jamieson|first4=Graham A.|last5=Kotchoubey|first5=Boris|last6=Kübler|first6=Andrea|last7=Lehmann|first7=Dietrich|last8=Miltner|first8=Wolfgang H. R.|last9=Ott|first9=Ulrich|last10=Pütz|first10=Peter|last11=Sammer|first11=Gebhard|last12=Strauch|first12=Inge|last13=Strehl|first13=Ute|last14=Wackermann|first14=Jiri|last15=Weiss|first15=Thomas|title=Psychobiology of Altered States of Consciousness.|journal=Psychological Bulletin|volume=131|issue=1|year=2005|pages=98–127|issn=1939-1455|doi=10.1037/0033-2909.131.1.98|pmid=15631555|s2cid=6909813}}</ref>
<ref name="ReferenceA">{{harvp|Blackmore|2003}}</ref> Nevertheless, much remains to be understood about the experience and its corresponding neurology, and the topic has been somewhat neglected in comparison with sleep and dreams; hypnagogia has been described as a "well-trodden and yet unmapped territory".<ref>{{harvp|Mavromatis|1987|p=xiii}}</ref>

Important reviews of the scientific literature have been made by Ghibellini & Meier,<ref>{{cite journal |last1=Ghibellini |first1=Romain |last2=Meier |first2=Beat |title=The hypnagogic state: A brief update |journal=Journal of Sleep Research |date=26 August 2022 |volume=32 |issue=1|article-number=e13719 |doi=10.1111/jsr.13719 |pmid=36017720 |pmc=10078162 }}</ref> Leaning,<ref>{{cite journal | author = Leaning F.E. | year = 1925 | title = An introductory study of hypnagogic phenomena | journal = Proceedings of the Society for Psychical Research | volume = 35 | pages = 289–409 }}</ref> [[Daniel Schacter|Schacter]],<ref name="Schachter"/> Richardson and Mavromatis.<ref name="mavromatis"/>

==Research==
Self-observation (spontaneous or systematic) was the primary tool of the early researchers. Since the late 20th century, this has been joined by questionnaire surveys and experimental studies. All three methods have their disadvantages as well as points to recommend them.<ref>{{harvp|Mavromatis|1987|p=286}}</ref>

Naturally, amnesia contributes to the difficulty of studying hypnagogia, as does the typically fleeting nature of hypnagogic experiences. These problems have been tackled by experimenters in several ways, including voluntary or induced interruptions,<ref name="Germaine, A. 1997 p. 243"/> sleep manipulation,<ref name="blackmore312"/> the use of techniques to "hover on the edge of sleep" thereby extending the duration of the hypnagogic state,<ref name="blackmore312">{{harvp|Blackmore|2003|p=314}}</ref> and training in the art of introspection to heighten the subject's powers of observation and attention.<ref name="blackmore312"/>

Techniques for extending hypnagogia range from informal (e.g. the subject holds up one of their arms as they go to sleep, to be awakened when it falls),<ref name="blackmore312"/> to the use of biofeedback devices to induce a "[[theta waves|theta]]" state – produced naturally the most when we are dreaming – characterized by relaxation and theta [[electroencephalogram|EEG]] activity.<ref>{{harvp|Mavromatis|1987|p=93}}</ref>

Another method is to induce a state said to be subjectively similar to sleep onset in a [[Ganzfeld effect|Ganzfeld]] setting, a form of [[sensory deprivation]]. But the assumption of identity between the two states may be unfounded. The average EEG spectrum in Ganzfeld is more similar to that of the relaxed waking state than to that of sleep onset.<ref name="Wackermann">Wackermann, Jiri, Pütz, Peter, Büchi, Simone, Strauch, Inge & Lehmann, Dietrich (2000). 'A comparison of Ganzfeld and hypnagogic state in terms of electrophysiological measures and subjective experience'. ''Proceedings of the 43rd Annual Convention of the Parapsychological Association'', pp. 302–15.</ref> Wackerman et al. conclude that "the Ganzfeld imagery, although subjectively very similar to that at sleep onset, should not be labelled as 'hypnagogic'. Perhaps a broader category of 'hypnagogic experience' should be considered, covering true hypnagogic imagery as well as subjectively similar imagery produced in other states."<ref name=" Wackermann"/>

==See also==
{{col div}}
* {{annotated link|False awakening}}
* {{annotated link|Nightmare}}
* {{annotated link|Night terror}}
* {{annotated link|Biphasic and polyphasic sleep}}
* {{annotated link|Sleep disorder}}
* {{annotated link|Yoga nidra}}
* {{annotated link|Dream yoga}}
* {{annotated link|Dreamachine}}
* {{Anl|Unihemispheric slow-wave sleep}}
{{colend}}

==References==
{{Reflist|30em}}

===Bibliography===
{{refbegin}}
*{{cite book|last=Blackmore|first=Susan|year=2003|title=Consciousness: an Introduction|publisher=London: Hodder & Stoughton|isbn=0-340-80909-4}}
*{{cite book|last=Mavromatis|first=Andreas|year=1987|title=Hypnagogia: the Unique State of Consciousness Between Wakefulness and Sleep|location=London|publisher=Routledge and Kegan Paul|isbn=0-7102-0282-2}}

{{refend}}

==Further reading==
*{{cite book |chapter=The Hypnagogic |title=The Head Trip: Adventures on the Wheel of Consciousness |chapter-url=https://archive.org/details/headtrip00jeff |chapter-url-access=registration |year=2007 |isbn=978-0-679-31408-0 |first=Jeff |last=Warren|publisher=Random House }}
*Sacks, Oliver (2012). "On the Threshold of Sleep". ''Hallucinations.'' {{ISBN|978-0307957245}}

== External links ==
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{{Wiktionary}}
* "[http://bjp.rcpsych.org/cgi/content/abstract/169/4/459 Hypnagogic and hypnopompic hallucinations: pathological phenomena?]" in the ''[[British Journal of Psychiatry]]''
* [https://web.archive.org/web/20071013131259/http://forteantimes.com/features/articles/227/hypnagogia.html "Hypnagogia" by Gary Lachman] in ''Fortean Times''
* [[Joe Nickell|Nickell, Joe]]. "The Pascagoula Abduction: A Case of Hypnagogia?" in Ballester-Olmos, V.J. and Heiden, Richard W. (Eds.), ''[https://www.academia.edu/101922617/The_Reliability_of_UFO_Witness_Testimony The Reliability of UFO Witness Testimony]''. UPIAR, Turin, Italy (2023), pp. 137-140. ISBN 9791281441002

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{{Use dmy dates|date=October 2019}}

[[Category:Sleep disorders]]
[[Category:Sleep physiology]]
[[Category: Lucid dreams]]
[[Category: Hallucinations]]