hypnagogic hallucination
   Also known as hypnagogic imagery, hypnagogic reverie, hypnagogic illusion, hypnagogic visualization, presomnal sensation, predormital hallucination, anthypnic sensation, oneirogagic image, phantasma, vision of half-sleep, and faces in the dark. The term hypnagogic hallucination is indebted to the Greek words hupnos (sleep) and agein (to lead, to transport). It translates roughly as 'a hallucination that leads the individual into sleep'. The Greek philosopher Aristotle (384-322 BC) has been credited with providing one of the earliest written references to hypnagogic hallucinations: "And indeed some very young persons, if it is dark, through looking with open eyes, see multitudes of phantom figures moving before them, so that they often cover up their heads in terror." The scientific study of these phenomena began in the 19th century with authors such as Johannes Peter Müller (1801-1858), Jules Gabriel François Baillarger (1806-1891), and Louis-Ferdinand-Alfred Maury (1817-1892). The term itself was introduced in or shortly before 1848 by Maury to denote a hallucination that occurs around the moment offalling asleep. Hypnagogic hallucinations (as well as their logical counterpart, referred to as " hypnopompic hallucinations) are perceptual phenomena taking place in the intermediate state between wakefulness and sleep. Taken together, hypnagogic and hypnopompic hallucinations are referred to as " hypnagogia. Hypnagogic hallucinations are regularly occurring phenomena in individuals with and without a mental disorder. Although Müller and other 19th-century authors reported a lifetime prevalence of only 2% in adults, more recent studies tend to report incidence rates of75% and higher. Some studies indicate that the incidence ofhypna-gogic hallucinations increases when accompanied by the use of - or withdrawal from - therapeutics such as tricyclic antidepressants and opioids. An increased incidence has also been reported in association with various psychiatric and neurological disorders, including narcolepsy, anxiety disorders, depressive disorder, bipolar disorder, and adjustment disorder. Hypnagogic hallucinations can be extremely rich and diverse in nature. They are sometimes distinguished from " dreams by their kaleidoscopically changing nature. It has also been argued that they are often experienced passively, whereas in dreams the subject tends to be personally involved. Hypnagogic hallucinations are usually of a visual, auditory, and/or tactile nature, although they can manifest themselves in any of the sensory modalities. The seeing of faces (i.e. "facial hallucinations) has been reported as one of their most common manifestations (hence the name 'faces in the dark'). Peculiar aspects of visual hypnagogic hallucinations include their 'strange luminosity', visions in the shape of " microptic images, " polyopia (i.e. seeing multiple images of a single object simultaneously), and " synaesthesia. Because they occur when the eyes are either closed or confronted with a dark environment, visual hypnagogic hallucinations are also classified as "closed-eye hallucinations. A classification of visual hypnagogic hallucinations devised by the Cypriot philosopher and psychologist Andreas Mavromatis, based on their phenomenological characteristics, comprises the categories 'formless', 'designs', 'faces', 'figures, animals, and objects', 'nature scenes', 'scenes with people', and 'print and writing'. It has been suggested that all these types of visual hypnagogic hallucinations can develop out of the idioretinal light or "Eigengrau, i.e. the greyish "visual noise that is normally seen in perfect darkness. Some common examples of nonverbal auditory hypn-agogic hallucinations are bangs, crashing noises, and explosions (referred to as the "exploding head syndrome), fragments of music, and the ringing of a door bell. Some common examples of verbal auditory hypnagogic hallucinations are the sound of one's name being called, apparently meaningless sounds, neologisms, quotes, seemingly irrelevant sentences, and references to spoken conversations or texts one has recently been reading. Hypnagogic hallucinations in general may be accompanied by " hallucinoid experiences such as " sensed presence, " incubus, and " illusory movement experiences. Phenomenologically, hyp-nagogic hallucinations meet all the Esquirolian criteria for hallucinations except that they occur during the transitional phase between wakeful-ness and sleep. As a consequence, they have traditionally been set apart from the class of " hallucinations proper. The mediation of hypna-gogic hallucinations is associated primarily with instances of REM sleep occurring in the absence of other REM phenomena. For this reason, they have also been designated as REM dissociation phenomena. These tend to occur during sleep onset (i.e. during stage N1 sleep as recorded on the electroencephalogram). Conceptually, the notion of hypnagogic hallucination is related to the notion of "phantasma as developed by the German physiologist and zoologist Johannes Peter Müller (1801-1858). A special variant of the group of hypnagogic hallucinations, with phenomena reminiscent of the early sensory history of the child, is known as the " Isakower phenomenon. "Nightmares occurring immediately upon falling asleep are referred to as " hypnagogic nightmares. In a phenomenolog-ical, and perhaps a pathophysiological sense as well, hypnagogic hallucinations would seem to be related to " desert hallucinations.
   References
   Aristotle (1984). On dreams.In: The complete works of Aristotle. The revised Oxford translation. Volume 1. Edited by Barnes, J. Princeton, NJ: Princeton University Press.
   Cheyne, J.A. (2001). The ominous numinous. Sensed presence and 'other' hallucinations. Journalof Consciousness Studies, 8, 133-150.
   Maury, L.F.A. (1848). Des hallucinations hypn-agogiques. Annales Médico-psychologiques, 11, 26-40.
   Mavromatis, A. (1987). Hypnagogia. The unique state of consciousness between wakefulness and sleep. London: Routledge.
   Watkins, M. (2003). Waking dreams. Third edition. Putnam, CT: Springer Publications.

Dictionary of Hallucinations. . 2010.

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