Hypnagogia is the experience of the transitional state from
wakefulness
Wakefulness is a daily recurring Human brain, brain state and state of consciousness in which an individual is conscious and engages in coherent cognition, cognitive and behavioral responses to the external world.
Being awake is the opposite of ...
to
sleep
Sleep is a sedentary state of mind and body. It is characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity and reduced interactions with surroundings. It is distinguished from wakefulness by a de ...
: the ''hypnagogic'' state of
consciousness
Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...
, during the onset of sleep. Its opposite state is described as the transitional state from sleep into wakefulness. Mental phenomena that may occur during this "threshold consciousness" phase include hypnagogic
hallucination
A hallucination is a perception in the absence of an external stimulus that has the qualities of a real perception. Hallucinations are vivid, substantial, and are perceived to be located in external objective space. Hallucination is a combinatio ...
s, lucid thought,
exploding head syndrome
Exploding head syndrome (EHS) is an abnormal sensory perception during sleep in which a person experiences auditory hallucinations that are loud and of short duration when falling asleep or waking up. The noise may be frightening, typically occ ...
,
lucid dream
A lucid dream is a type of dream in which the dreamer becomes aware that they are dreaming while dreaming. During a lucid dream, the dreamer may gain some amount of control over the dream characters, narrative, or environment; however, this is n ...
ing, and
sleep paralysis
Sleep paralysis is a state, during waking up or falling asleep, in which one is conscious but is completely paralyzed. During an episode, one may hallucinate (hear, feel, or see things that are not there), which often results in fear. Episodes ...
. The latter two phenomena are themselves separate sleep conditions that are sometimes experienced during the hypnagogic state.
Definitions
The word ''hypnagogia'' is sometimes used in a restricted
sense
A sense is a biological system used by an organism for sensation, the process of gathering information about the world through the detection of Stimulus (physiology), stimuli. (For example, in the human body, the brain which is part of the cen ...
to refer to the onset of sleep, and contrasted with ''
hypnopompia
Hypnopompia (also known as hypnopompic state) is the state of consciousness leading out of sleep, a term coined by the psychical researcher Frederic Myers. Its mirror is the hypnagogic state at sleep onset; though often conflated, the two state ...
'',
Frederic Myers
Revd Frederic Myers (20 September 1811, Blackheath, London – 20 July 1851, Clifton, Cumberland) was a Church of England clergyman and author.
He was the son of Thomas Myers (1774–1834), mathematician and geographer, and his wife, Anna Maria ...
's term for waking up. 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
A phenomenon ( : phenomena) is an observable event. The term came into its modern philosophical usage through Immanuel Kant, who contrasted it with the noumenon, which ''cannot'' be directly observed. Kant was heavily influenced by Gottfried W ...
to one or the other, given that the same kinds of
experience
Experience refers to conscious events in general, more specifically to perceptions, or to the practical knowledge and familiarity that is produced by these conscious processes. Understood as a conscious event in the widest sense, experience involv ...
occur in both, and that people may drift in and out of sleep. In this article ''hypnagogia'' will be used in the broader sense, unless otherwise stated or implied.
Other terms for hypnagogia, in one or both senses, that have been proposed include "presomnal" or "anthypnic sensations", "visions of half-sleep", "oneirogogic images" and "phantasmata", "the borderland of sleep", "praedormitium", "borderland state", "half-dream state", "pre-dream condition", "sleep onset dreams",Stickgold, R., interviewed 30 October 2000 by
Norman Swan
Norman Swan (born Norman Swirsky in 1953) is a Scottish-born Australian physician, journalist and broadcaster.
Life and career
Swan was born in Scotland as Norman Swirsky. ; 1953)Datelines: Norman Swan, ''Sydney Morning Herald'', 7 November 19 ...
for ''
The Health Report
''The'' () is a grammatical article in English, denoting persons or things already mentioned, under discussion, implied or otherwise presumed familiar to listeners, readers, or speakers. It is the definite article in English. ''The'' is the m ...
'' on Australia's
Radio National
Radio National, known on-air as RN, is an Australia-wide public service broadcasting radio network run by the Australian Broadcasting Corporation (ABC). From 1947 until 1985, the network was known as ABC Radio 2.
History
1937: Predecessors an ...
transcript . Retrieved 3 July 2008. "dreamlets", and "wakefulness-sleep transition" (WST).
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
Meditation is a practice in which an individual uses a technique – such as mindfulness, or focusing the mind on a particular object, thought, or activity – to train attention and awareness, and achieve a mentally clear and emotionally cal ...
.
Signs and symptoms
Transition to and from sleep may be attended by a wide variety of sensory experiences. These can occur in any modality, individually or combined, and range from the vague and barely perceptible to vivid
hallucination
A hallucination is a perception in the absence of an external stimulus that has the qualities of a real perception. Hallucinations are vivid, substantial, and are perceived to be located in external objective space. Hallucination is a combinatio ...
s.
Sights
Among the more commonly reported, and more thoroughly researched, sensory features of hypnagogia are
phosphenes
A phosphene is the phenomenon of seeing light without light entering the eye. The word ''phosphene'' comes from the Greek words ''phos'' (light) and ''phainein'' (to show). Phosphenes that are induced by movement or sound may be associated wit ...
which can manifest as seemingly random speckles, lines or geometrical patterns, including
form constants
A form constant is one of several geometric patterns which are recurringly observed during hypnagogia, hallucinations and altered states of consciousness.
History
In 1926, Heinrich Klüver systematically studied the effects of mescaline (peyote ...
images
An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensiona ...
. They may be
monochromatic
A monochrome or monochromatic image, object or color scheme, palette is composed of one color (or lightness, values of one color). Images using only Tint, shade and tone, shades of grey are called grayscale (typically digital) or Black and wh ...
or richly coloured, still or moving, flat or three-dimensional (offering an impression of 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, although others understand the state rather as a gradual transition from hypnagogia to fragmentary dreams, i.e., from simple '' Eigenlicht'' to whole 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 Lecoq, Baron d'Hervey de Juchereau, Marquis d'Hervey de Saint-Denys (; 6 May 1822 – 2 November 1892) son of Pierre Marin Alexandre Le Coq or Lecoq, Baron d'Hervey (1780-1858), and Marie Louise Josephine Mélanie Juchereau ...
.
''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
drowsy
Somnolence (alternatively sleepiness or drowsiness) is a state of strong desire for sleep, or sleeping for unusually long periods (compare hypersomnia). It has distinct meanings and causes. It can refer to the usual state preceding falling asleep ...
, a tendency dubbed the '' Tetris'' effect. This effect has even been observed in
amnesia
Amnesia is a deficit in memory caused by brain damage or disease,Gazzaniga, M., Ivry, R., & Mangun, G. (2009) Cognitive Neuroscience: The biology of the mind. New York: W.W. Norton & Company. but it can also be caused temporarily by the use ...
cs who otherwise have no
memory
Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...
of the original activity. When the activity involves moving objects, as in the video game ''
Tetris
''Tetris'' (russian: link=no, Тетрис) is a puzzle video game created by Soviet software engineer Alexey Pajitnov in 1984. It has been published by several companies for multiple platforms, most prominently during a dispute over the approp ...
'', 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
Robert Stickgold is a full professor of psychiatry at the Harvard Medical School and the Beth Israel Deaconess Medical Center. A sleep researcher, his work focuses on the relationship between sleep and learning. His articles in the popular press ...
recounts having experienced the touch of rocks while falling asleep after mountain climbing. 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. Many
chess
Chess is a board game for two players, called White and Black, each controlling an army of chess pieces in their color, with the objective to checkmate the opponent's king. It is sometimes called international chess or Western chess to disti ...
players report the phenomenon of seeing the chessboard and pieces during this state. New employees working stressful and demanding jobs often report feeling the experience of performing work-related tasks in this period before sleep.
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
Exploding head syndrome (EHS) is an abnormal sensory perception during sleep in which a person experiences auditory hallucinations that are loud and of short duration when falling asleep or waking up. The noise may be frightening, typically occ ...
). People may imagine their own name called, crumpling bags, white noise, or a doorbell ringing. Snatches of imagined
speech
Speech is a human vocal communication using language. Each language uses Phonetics, phonetic combinations of vowel and consonant sounds that form the sound of its words (that is, all English words sound different from all French words, even if ...
are common. While typically
nonsensical
Nonsense is a communication, via speech, writing, or any other symbolic system, that lacks any coherent meaning. Sometimes in ordinary usage, nonsense is synonymous with absurdity or the ridiculous. Many poets, novelists and songwriters have use ...
and fragmented, these speech events can occasionally strike the individual as apt comments on—or summations of—their
thought
In their most common sense, the terms thought and thinking refer to conscious cognitive processes that can happen independently of sensory stimulation. Their most paradigmatic forms are judging, reasoning, concept formation, problem solving, a ...
s at the time. They often contain
word play
Word play or wordplay (also: play-on-words) is a literary technique and a form of wit in which words used become the main subject of the work, primarily for the purpose of intended effect or amusement. Examples of word play include puns, phonet ...
,
neologism
A neologism Greek νέο- ''néo''(="new") and λόγος /''lógos'' meaning "speech, utterance"] is a relatively recent or isolated term, word, or phrase that may be in the process of entering common use, but that has not been fully accepted int ...
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.
Other sensations
Gustatory
The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste (flavor). Taste is the perception produced or stimulated when a substance in the mouth reacts chemically with taste receptor ...
,
olfactory
The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste.
In humans, it ...
and
thermal
A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...
sensations in hypnagogia have all been reported, as well as
tactile
Tactile may refer to:
* Tactile, related to the sense of touch
* Haptics (disambiguation)
* Tactile (device), a text-to-braille translation device
See also
* Tangibility, in law
* Somatosensory system, where sensations are processed
* CD96
CD9 ...
sensations (including those kinds classed as
paresthesia
Paresthesia is an abnormal sensation of the skin (tingling, pricking, chilling, burning, numbness) with no apparent physical cause. Paresthesia may be transient or chronic, and may have any of dozens of possible underlying causes. Paresthesias ar ...
or
formication
Formication is the sensation resembling that of small insects crawling on (or under) the skin when nothing is actually there. It is one specific form of a set of sensations known as paresthesias, which also include the more common prickling, tin ...
). Sometimes there is
synesthesia
Synesthesia (American English) or synaesthesia (British English) is a perceptual phenomenon in which stimulation of one sensory or cognitive pathway leads to involuntary experiences in a second sensory or cognitive pathway. People who re ...
; many people report seeing a flash of light or some other visual image in response to a real sound.
Proprioceptive
Proprioception ( ), also referred to as kinaesthesia (or kinesthesia), is the sense of self-movement, force, and body position. It is sometimes described as the "sixth sense".
Proprioception is mediated by proprioceptors, mechanosensory neurons ...
effects may be noticed, with numbness and changes in perceived body size and proportions, feelings of floating or bobbing as if their bed were a boat, and
out-of-body experience
An out-of-body experience (OBE or sometimes OOBE) is a phenomenon in which a person perceives the world from a location outside their physical body. An OBE is a form of autoscopy (literally "seeing self"), although this term is more commonly use ...
s. Perhaps the most common experience of this kind is the falling sensation, and associated
hypnic jerk
A hypnic jerk, hypnagogic jerk, sleep start, sleep twitch, myoclonic jerk, or night start is a brief and sudden involuntary contraction of the muscles of the body which occurs when a person is beginning to fall asleep, often causing the person t ...
, encountered by many people, at least occasionally, while drifting off to sleep.
Cognitive and affective phenomena
Thought
In their most common sense, the terms thought and thinking refer to conscious cognitive processes that can happen independently of sensory stimulation. Their most paradigmatic forms are judging, reasoning, concept formation, problem solving, a ...
processes on the edge of sleep tend to differ radically from those of ordinary wakefulness. For example, something that you agreed with within a state of hypnagogia may seem completely ridiculous to you in an awake state. Hypnagogia may involve a "loosening of
ego
Ego or EGO may refer to:
Social sciences
* Ego (Freudian), one of the three constructs in Sigmund Freud's structural model of the psyche
* Egoism, an ethical theory that treats self-interest as the foundation of morality
* Egotism, the drive to ...
boundaries ... openness, sensitivity, internalization-subjectification of the physical and mental environment (
empathy
Empathy is the capacity to understand or feel what another person is experiencing from within their frame of reference, that is, the capacity to place oneself in another's position. Definitions of empathy encompass a broad range of social, co ...
) and diffuse-absorbed
attention
Attention is the behavioral and cognitive process of selectively concentrating on a discrete aspect of information, whether considered subjective or objective, while ignoring other perceivable information. William James (1890) wrote that "Atte ...
." Hypnagogic
cognition
Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...
, in comparison with that of normal, alert wakefulness, is characterized by heightened
suggestibility
Suggestibility is the quality of being inclined to accept and act on the suggestions of others. One may fill in gaps in certain memories with false information given by another when recalling a scenario or moment. Suggestibility uses cues to disto ...
, illogic and a fluid association of
idea
In common usage and in philosophy, ideas are the results of thought. Also in philosophy, ideas can also be mental representational images of some object. Many philosophers have considered ideas to be a fundamental ontological category of being ...
s. Subjects are more receptive in the hypnagogic state to
suggestion
Suggestion is the psychological process by which a person guides their own or another person's desired thoughts, feelings, and behaviors by presenting stimuli that may elicit them as reflexes instead of relying on conscious effort.
Nineteenth-ce ...
from an experimenter than at other times, and readily incorporate external
stimuli
A stimulus is something that causes a physiological response. It may refer to:
*Stimulation
**Stimulus (physiology), something external that influences an activity
**Stimulus (psychology), a concept in behaviorism and perception
*Stimulus (economi ...
into hypnagogic trains of thought and subsequent dreams. This receptivity has a
physiological
Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...
parallel;
EEG
Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex ...
readings show elevated responsiveness to sound around the onset of sleep.
Herbert Silberer
Herbert Silberer (February 28, 1882 – January 12, 1923) was a Viennese psychoanalyst involved with the professional circle surrounding Sigmund Freud which included other pioneers of psychological study as Carl Gustav Jung, Alfred Adler and othe ...
described a process he called ''autosymbolism'', whereby hypnagogic hallucinations seem to represent, without repression or censorship, whatever one is thinking at the time, turning abstract
idea
In common usage and in philosophy, ideas are the results of thought. Also in philosophy, ideas can also be mental representational images of some object. Many philosophers have considered ideas to be a fundamental ontological category of being ...
s into a concrete
image
An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensiona ...
, which may be perceived as an apt and succinct representation thereof.
The hypnagogic state can provide
insight
Insight is the understanding of a specific cause and effect within a particular context. The term insight can have several related meanings:
*a piece of information
*the act or result of understanding the inner nature of things or of seeing intu ...
into a
problem
Problem solving is the process of achieving a goal by overcoming obstacles, a frequent part of most activities. Problems in need of solutions range from simple personal tasks (e.g. how to turn on an appliance) to complex issues in business an ...
, the best-known example being
August Kekulé
Friedrich August Kekulé, later Friedrich August Kekule von Stradonitz ( , ; 7 September 1829 – 13 July 1896), was a German organic chemist. From the 1850s until his death, Kekulé was one of the most prominent chemists in Europe, especially ...
’s realization that the structure of
benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...
was a closed ring while half-asleep in front of a fire and seeing molecules forming into snakes, one of which grabbed its tail in its mouth. Many other artists, writers, scientists and inventors – including
Beethoven
Ludwig van Beethoven (baptised 17 December 177026 March 1827) was a German composer and pianist. Beethoven remains one of the most admired composers in the history of Western music; his works rank amongst the most performed of the classical ...
,
Richard Wagner
Wilhelm Richard Wagner ( ; ; 22 May 181313 February 1883) was a German composer, theatre director, polemicist, and conductor who is chiefly known for his operas (or, as some of his mature works were later known, "music dramas"). Unlike most op ...
,
Walter Scott
Sir Walter Scott, 1st Baronet (15 August 1771 – 21 September 1832), was a Scottish novelist, poet, playwright and historian. Many of his works remain classics of European and Scottish literature, notably the novels ''Ivanhoe'', ''Rob Roy (n ...
,
Salvador Dalí
Salvador Domingo Felipe Jacinto Dalí i Domènech, Marquess of Dalí of Púbol (; ; ; 11 May 190423 January 1989) was a Spanish Surrealism, surrealist artist renowned for his technical skill, precise draftsmanship, and the striking and bizarr ...
,
Thomas Edison
Thomas Alva Edison (February 11, 1847October 18, 1931) was an American inventor and businessman. He developed many devices in fields such as electric power generation, mass communication, sound recording, and motion pictures. These inventio ...
Isaac Newton
Sir Isaac Newton (25 December 1642 – 20 March 1726/27) was an English mathematician, physicist, astronomer, alchemist, theologian, and author (described in his time as a "natural philosopher"), widely recognised as one of the grea ...
– have credited hypnagogia and related states with enhancing their creativity. A 2001 study by Harvard psychologist
Deirdre Barrett
Deirdre Barrett is an American author and psychologist known for her research on dreams, hypnosis and imagery, and has written on evolutionary psychology. Barrett is a teacher at Harvard Medical School, and a past president of the International ...
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.
A feature that hypnagogia shares with other stages of sleep is
amnesia
Amnesia is a deficit in memory caused by brain damage or disease,Gazzaniga, M., Ivry, R., & Mangun, G. (2009) Cognitive Neuroscience: The biology of the mind. New York: W.W. Norton & Company. but it can also be caused temporarily by the use ...
. But this is a selective forgetfulness, affecting the
hippocampal
The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, an ...
memory system, which is responsible for
episodic
Episodic may refer to:
* The nature of television series that are divided into short programs known as episodes
* Episodic memory, types of memory that result from specific incidents in a lifetime
* In Geology, episodic refers to events that occur ...
or
autobiographical memory
Autobiographical memory is a memory system consisting of episodes recollected from an individual's life, based on a combination of episodic (personal experiences and specific objects, people and events experienced at particular time and place) a ...
, rather than the
neocortical
The neocortex, also called the neopallium, isocortex, or the six-layered cortex, is a set of layers of the mammalian cerebral cortex involved in higher-order brain functions such as sensory perception, cognition, generation of motor commands, sp ...
memory system, responsible for
semantic memory
Semantic memory refers to general world knowledge that humans have accumulated throughout their lives. This general knowledge (word meanings, concepts, facts, and ideas) is intertwined in experience and dependent on culture. We can learn about n ...
. It has been suggested that hypnagogia and
REM sleep
Rapid eye movement sleep (REM sleep or REMS) is a unique phase of sleep in mammals and birds, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the sleeper to dream viv ...
help in the consolidation of semantic memory, but the evidence for this has been disputed. For example, suppression of REM sleep due to
antidepressant
Antidepressants are a class of medication used to treat major depressive disorder, anxiety disorders, chronic pain conditions, and to help manage addictions. Common side-effects of antidepressants include dry mouth, weight gain, dizziness, hea ...
s and
lesion
A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals.
Types
There is no designated classifi ...
s to the
brainstem
The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is cont ...
has not been found to produce detrimental effects on cognition.
Hypnagogic phenomena may be interpreted as
visions
Vision, Visions, or The Vision may refer to:
Perception Optical perception
* Visual perception, the sense of sight
* Visual system, the physical mechanism of eyesight
* Computer vision, a field dealing with how computers can be made to gain un ...
,
prophecies
In religion, a prophecy is a message that has been communicated to a person (typically called a ''prophet'') by a supernatural entity. Prophecies are a feature of many cultures and belief systems and usually contain divine will or law, or prete ...
,
premonitions
Precognition (from the Latin 'before', and 'acquiring knowledge') is the purported psychic phenomenon of seeing, or otherwise becoming directly aware of, events in the future.
There is no accepted scientific evidence that precognition is a ...
,
apparitions
Apparition may refer to:
Supernatural
*Apparitional experience, an anomalous, quasi-perceptual experience
* A vision, something seen in a dream, trance, or religious ecstasy
*Ghost, the soul or spirit of a dead person or animal that can appear ...
and inspiration (
artistic
Art is a diverse range of human activity, and resulting product, that involves creative or imaginative talent expressive of technical proficiency, beauty, emotional power, or conceptual ideas.
There is no generally agreed definition of wh ...
or
divine
Divinity or the divine are things that are either related to, devoted to, or proceeding from a deity.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
Non-rapid eye movement sleep (NREM), also known as quiescent sleep, is, collectively, sleep stages 1–3, previously known as stages 1–4. Rapid eye movement sleep (REM) is not included. There are distinct electroencephalographic and other char ...
, but may also occur with pre-sleep
alpha wave
Alpha waves, or the alpha rhythm, are neural oscillations in the frequency range of 8–12 Hz likely originating from the synchronous and coherent (in phase or constructive) electrical activity of thalamic pacemaker cells in humans. Historica ...
s. Davis et al. found short flashes of dreamlike imagery at the onset of sleep to correlate with drop-offs in alpha
EEG
Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex ...
activity. Hori et al. regard sleep onset hypnagogia as a state distinct from both wakefulness and sleep with unique
electrophysiological
Electrophysiology (from Greek , ''ēlektron'', "amber" etymology of "electron"">Electron#Etymology">etymology of "electron" , ''physis'', "nature, origin"; and , ''-logia'') is the branch of physiology that studies the electrical properties of bi ...
,
behavior
Behavior (American English) or behaviour (British English) is the range of actions and mannerisms made by individuals, organisms, systems or artificial entities in some environment. These systems can include other systems or organisms as wel ...
al and subjective characteristics, while Germaine et al. have demonstrated a resemblance between the EEG
power spectra
The power spectrum S_(f) of a time series x(t) describes the distribution of power into frequency components composing that signal. According to Fourier analysis, any physical signal can be decomposed into a number of discrete frequencies, ...
of spontaneously occurring hypnagogic images, on the one hand, and those of both
REM sleep
Rapid eye movement sleep (REM sleep or REMS) is a unique phase of sleep in mammals and birds, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the sleeper to dream viv ...
and relaxed wakefulness, on the other.
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
Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter aleph , whic ...
(stages 1–3), suppressed waves of less than 20μV (stage 4),
theta
Theta (, ; uppercase: Θ or ; lowercase: θ or ; grc, ''thē̂ta'' ; Modern: ''thī́ta'' ) is the eighth letter of the Greek alphabet, derived from the Phoenician letter Teth . In the system of Greek numerals, it has a value of 9.
Gr ...
ripples (stage 5), proportions of sawtooth waves (stages 6–7), and presence of spindles (stages 8–9).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. Germaine and Nielsen found spontaneous hypnagogic imagery to occur mainly during Hori sleep onset stages 4 (EEG flattening) and 5 (theta ripples).
The "covert-rapid-eye-movement" hypothesis proposes that hidden elements of
REM sleep
Rapid eye movement sleep (REM sleep or REMS) is a unique phase of sleep in mammals and birds, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the sleeper to dream viv ...
emerge during the wakefulness-sleep transition stage.
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.
Respiratory
The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies grea ...
pattern changes have also been noted in the hypnagogic state, in addition to a lowered rate of
frontalis muscle
The frontalis muscle () is a muscle which covers parts of the forehead of the skull. Some sources consider the frontalis muscle to be a distinct muscle. However, Terminologia Anatomica currently classifies it as part of the occipitofrontalis muscle ...
activity.
Daydreaming and waking reveries
Microsleep
A microsleep is a sudden temporary episode of sleep or drowsiness which may last for a few seconds where an individual fails to respond to some arbitrary sensory input and becomes unconscious.International Classification of Sleep Disorders, , pa ...
(short episodes of immediate sleep onset) may intrude into wakefulness at any time in the wakefulness-sleep cycle, due to
sleep deprivation
Sleep deprivation, also known as sleep insufficiency or sleeplessness, is the condition of not having adequate duration and/or quality of sleep to support decent alertness, performance, and health. It can be either chronic or acute and may vary ...
and other conditions, resulting in impaired cognition and even amnesia.
In his book, ''
Zen and the Brain
''Zen and the Brain: Toward an Understanding of Meditation and Consciousness'' is a 1998 book by neurologist and Zen practitioner James H. Austin, in which the author attempts to establish links between the neurology, neurological workings of the h ...
'',
James H. Austin
James H. Austin is an American neurologist and author. He is the author of the book ''Zen and the Brain''. It establishes links between the neurophysiology of the human brain and the practice of meditation, and won the Scientific and Medical Netw ...
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.
History
Early references to hypnagogia are to be found in the writings of
Aristotle
Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...
,
Iamblichus
Iamblichus (; grc-gre, Ἰάμβλιχος ; Aramaic: 𐡉𐡌𐡋𐡊𐡅 ''Yamlīḵū''; ) was a Syrian neoplatonic philosopher of Arabic origin. He determined a direction later taken by neoplatonism. Iamblichus was also the biographer of ...
Simon Forman
Simon Forman (31 December 1552 – 5 or 12 September 1611) was an Elizabethan astrologer, occultist and herbalist active in London during the reigns of Queen Elizabeth I and James I of England. His reputation, however, was severely tarnishe ...
, and
Swedenborg
Emanuel Swedenborg (, ; born Emanuel Swedberg; 29 March 1772) was a Swedish pluralistic-Christian theologian, scientist, philosopher and mystic. He became best known for his book on the afterlife, ''Heaven and Hell'' (1758).
Swedenborg had a ...
.
Romanticism
Romanticism (also known as the Romantic movement or Romantic era) was an artistic, literary, musical, and intellectual movement that originated in Europe towards the end of the 18th century, and in most areas was at its peak in the approximate ...
brought a renewed interest in the subjective experience of the edges of sleep. In more recent centuries, many authors have referred to the state;
Edgar Allan Poe
Edgar Allan Poe (; Edgar Poe; January 19, 1809 – October 7, 1849) was an American writer, poet, editor, and literary critic. Poe is best known for his poetry and short stories, particularly his tales of mystery and the macabre. He is wide ...
, for example, wrote of the "fancies" he experienced "only when I am on the brink of sleep, with the consciousness that I am so."
The serious scientific inquiry began in the 19th century with
Johannes Peter Müller
Johannes Peter Müller (14 July 1801 – 28 April 1858) was a German physiologist, comparative anatomy, comparative anatomist, ichthyology, ichthyologist, and herpetology, herpetologist, known not only for his discoveries but also for his ability ...
,
Jules Baillarger
Jules Baillarger, full name Jules Gabriel François Baillarger (25 March 1809 – 31 December 1890), was a French neurologist and psychiatrist.
Biography
Baillarger was born in Montbazon, France. He studied medicine at the University of Paris un ...
, and
Alfred Maury
Louis Ferdinand Alfred Maury (March 23, 1817 – February 11, 1892), was a French scholar and physician, important because his ideas about the interpretation of dreams and the effect of external stimuli on dreams pre-dated those of Sigmund Fre ...
, and continued into the 20th century with Leroy.
Charles Dickens' ''Oliver Twist'' contains an elaborate description of the hypnagogic state in Chapter XXXIV.
The advent of
electroencephalography
Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex ...
(EEG) has 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, and continues with increasing sophistication. While the dominance of the
behaviorist
Behaviorism is a systematic approach to understanding the behavior of humans and animals. It assumes that behavior is either a reflex evoked by the pairing of certain antecedent stimuli in the environment, or a consequence of that individual' ...
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
An altered state of consciousness (ASC), also called altered state of mind or mind alteration, is any condition which is significantly different from a normal waking state. By 1892, the expression was in use in relation to hypnosis, though there ...
playing an important role in the emerging multidisciplinary study of
consciousness
Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...
. 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".
The word ''hypnagogia'' entered the popular psychology literature through Dr. Andreas Mavromatis in his 1983 thesis, while ''hypnagogic'' and ''hypnopompic'' were coined by others in the 1800s and noted by
Havelock Ellis
Henry Havelock Ellis (2 February 1859 – 8 July 1939) was an English physician, eugenicist, writer, progressive intellectual and social reformer who studied human sexuality. He co-wrote the first medical textbook in English on homosexuality in ...
. The term ''hypnagogic'' was originally coined by
Alfred Maury
Louis Ferdinand Alfred Maury (March 23, 1817 – February 11, 1892), was a French scholar and physician, important because his ideas about the interpretation of dreams and the effect of external stimuli on dreams pre-dated those of Sigmund Fre ...
to name the state of consciousness during the onset of sleep. ''Hypnopompic'' was coined by
Frederic Myers
Revd Frederic Myers (20 September 1811, Blackheath, London – 20 July 1851, Clifton, Cumberland) was a Church of England clergyman and author.
He was the son of Thomas Myers (1774–1834), mathematician and geographer, and his wife, Anna Maria ...
soon afterwards to denote the onset of
wakefulness
Wakefulness is a daily recurring Human brain, brain state and state of consciousness in which an individual is conscious and engages in coherent cognition, cognitive and behavioral responses to the external world.
Being awake is the opposite of ...
. The term ''hypnagogia'' is used by Dr. Mavromatis to identify the study of the sleep-transitional consciousness states in general, and he employs ''hypnagogic'' (toward sleep) or ''hypnopompic'' (from sleep) to identify the specific experiences under study.
Important reviews of the scientific literature have been made by Leaning, Schacter, Richardson and 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.
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, sleep manipulation, the use of techniques to "hover on the edge of sleep" thereby extending the duration of the hypnagogic state, and training in the art of introspection to heighten the subject's powers of observation and attention.
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), to the use of biofeedback devices to induce a "
theta
Theta (, ; uppercase: Θ or ; lowercase: θ or ; grc, ''thē̂ta'' ; Modern: ''thī́ta'' ) is the eighth letter of the Greek alphabet, derived from the Phoenician letter Teth . In the system of Greek numerals, it has a value of 9.
Gr ...
" state – produced naturally the most when we are dreaming – characterized by relaxation and theta
EEG
Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex ...
activity.
Another method is to induce a state said to be subjectively similar to sleep onset in a
Ganzfeld Ganzfeld (German for "complete field") is a particular phenomenon of visual perception. The term is used most commonly in relationship to:
* Ganzfeld effect, the psychological result of staring at an actual Ganzfeld
* Ganzfeld experiment
A gan ...
setting, a form of
sensory deprivation
Sensory deprivation or perceptual isolation is the deliberate reduction or removal of stimuli from one or more of the senses. Simple devices such as blindfolds or hoods and earmuffs can cut off sight and hearing, while more complex devices can al ...
. 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.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. 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."
See also
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References
Bibliography
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Further reading
*
*Sacks, Oliver (2012). "On the Threshold of Sleep". ''Hallucinations.''
British Journal of Psychiatry
The ''British Journal of Psychiatry'' is a peer-reviewed medical journal covering all branches of psychiatry with a particular emphasis on the clinical aspects of each topic.
The journal is owned by the Royal College of Psychiatrists and publis ...