Hallucination
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226126843
2008-07-16T22:54:49Z
Ira Silva
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+iw
A '''hallucination''' in the broadest sense is a [[perception]] in the absence of a [[stimulus (physiology)|stimulus]]. In a stricter sense, hallucinations are defined as perceptions in a conscious and awake state in the absence of external stimuli and that have qualities of real perception in that they are vivid, substantial, and located in external objective space. These definitions distinguish hallucinations from the related phenomena of [[dream]]ing (no consciousness), [[illusion]] (distorted or misinterpreted real perception), [[imagery]] (does not mimic real perception and is under voluntary control), and [[pseudohallucination]] (does not mimick real perception, but is not under voluntary control).<ref name="Chiu">{{cite journal
| author = Leo P. W. Chiu
| year = 1989
| title = Differential diagnosis and management of hallucinations
| journal = Journal of the Hong Kong Medical Association
| volume = 41
| issue = 3
| pages = 292–297
| doi =
| url = http://sunzi1.lib.hku.hk/hkjo/view/21/2100448.pdf
}}</ref>
Hallucinations also differ from "delusional perceptions", in which a correctly sensed and interpreted genuine perception is given some additional (and typically bizarre) significance.
Hallucinations may occur in any sensory modality—[[visual system|visual]], [[auditory system|auditory]], [[olfaction|olfactory]], [[taste|gustatory]], [[tactition|tactile]], [[proprioception|proprioceptive]], [[equilibrioception|equilibrioceptive]], [[nociception|nociceptive]], and [[thermoception|thermoceptive]].
A mild form of hallucination is known as a disturbance, and can occur in any of the senses above. These may be things like seeing movement in [[peripheral vision]], or hearing faint noises and voices.
[[Hypnagogic hallucination]]s and [[hypnopompia|hypnopompic hallucination]]s are considered normal phenomena. Hypnagogic hallucinations can occur as one is falling asleep and hypnopompic hallucinations occur when one is waking up. Hallucinations may also be associated with [[Psychoactive drug|drug]] use (particularly [[deliriants]]), [[sleep deprivation]], [[psychosis]], [[neurological disorder]]s, and [[delirium tremens]].
==Prevalence==
Studies have now shown hallucinatory experiences take place across the world. Previous studies, one as early as 1894,<ref>Sidgwick, H., Johnson, A, Myers, FWH et al (1894) Report on the census of hallucinations. ''Proceedings of the Society for Psychical Research'', 34, 25-394.<br></ref> have reported that approximately 10% of the population experience hallucinations. A recent survey of over 13,000 people<ref>[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11166087&dopt=Abstract Ohayon MM. (2000)] Prevalence of hallucinations and their pathological associations in the general population. ''Psychiatry Research'', 97(2-3), 153-64.<br></ref> reported a much higher figure with almost 39% of people reported hallucinatory experiences, 27% of which reported daytime hallucinations, mostly outside the context of illness or drug use. From this survey, [[olfactory]] (smell) and [[gustatory]] (taste) hallucinations seem the most common in the general population.
==Auditory hallucinations==
[[Sound|Auditory]] hallucinations, particularly of one or more talking voices, are particularly associated with [[psychosis|psychotic]] disorders such as [[schizophrenia]], and hold special significance in diagnosing these conditions, although many people not suffering from diagnosable [[mental illness]] may sometimes hear voices as well.<ref>{{cite web | url = http://www.livescience.com/humanbiology/060915_hearing_voices.html | title = Hearing Voices: Some People Like It | last = Thompson | first = Andrea | publisher = LiveScience.com | date = [[September 15]], [[2006]]|accessdate = 2006-11-25 }}</ref> The [[Hearing Voices Movement]] is a support and advocacy group for people who hallucinate voices, but do not otherwise show signs of mental illness or impairment. Other types of auditory hallucinations include musical hallucinations, where people will hear music playing in their mind, usually songs they are familiar with. One reason this can be caused is by [[lesions]] on the [[brain stem]], occurring most often from [[strokes]], but also [[tumors]], encephalitis, or [[abscesses]].<ref>{{cite web | url = http://www.sciencedaily.com/releases/2000/08/000809065249.htm | title = Rare Hallucinations Make Music In The Mind | publisher = ScienceDaily.com | date = [[August 9]], [[2000]] | accessdate = 2006-12-31 }}</ref> Other reasons include hearing loss and epileptic activity. Recent reports have also mentioned that it is also possible to get musical hallucinations from listening to music for long periods of time.<ref>{{cite web | url = http://www.vnunet.com/vnunet/news/2140422/ipod-help-produce-musical | title = IPod hallucinations face acid test | last = Young | first = Ken | publisher = Vnunet.com | date = [[July 27]], [[2005]] | accessdate = 2008-04-10 }}</ref>
===Hypnagogic hallucination===
{{main|Hypnagogia}}
These hallucinations occur just before falling asleep and affect a surprising number of people in the population. The hallucinations can last from seconds to minutes, all the while the subject usually remains aware of the true nature of the images. These are usually associated with [[narcolepsy]], but can also affect normal minds. Hypnagogic hallucinations are sometimes associated with brainstem abnormalities, but this is rare.<ref name=manford> [http://brain.oxfordjournals.org/cgi/content/abstract/121/10/1819 Manford and Andermann (1998)] Complex visual hallucinations. Clinical and Neurobiological insights''Brain'', 121(10), 1819-1840.</ref>
===Peduncular hallucinosis===
Peduncular means pertaining to the [[peduncle]], which is a neural tract running to and from the [[pons]] on the [[brain stem]]. These hallucinations occur most often in the evenings, but not during drowsiness as in the case of hypnagogic hallucination. The subject is usually fully conscious and can interact with the hallucinatory characters for extended periods of time. As in the case of [[hypnagogic hallucinations]], insight into the nature of the images remains intact. The false images can occur in any part of the visual field, and are rarely [[wikt:polymodal|polymodal]].<ref name=manford/>
===Delirium tremens===
{{main|Delirium tremens}}
One of the most enigmatic forms of visual hallucinations are the highly variable, possibly polymodal [[delirium tremens]]. Individuals suffering from delerium tremens may be agitated and confused, especially in the later stages of this disease. Insight is gradually reduced with the progression of this disorder. Sleep is disturbed and occurs for a shorter period of time, with [[REM overflow]].<ref name=manford/>
===Parkinson's disease and Lewy body dementia===
[[Parkinson's disease]] is linked with [[Dementia with Lewy bodies|Lewy body dementia]] for their similar hallucinatory symptoms. The symptoms strike during the evening in any part of the visual field and are rarely polymodal. The segue into hallucinations may start with illusions<ref>[http://www.nytimes.com/2006/02/14/health/14case.html?ex=1151121600&en=04560d31e7926bee&ei=5070 Mark Derr (2006)] Marilyn and Me, "The New York Times" [[February 14]], [[2006]] <br></ref> where sensory perception is greatly distorted, but no novel sensory information is present. These typically last for several minutes, during which time the subject may be either conscious and normal or drowsy/inaccessible. Insight into these hallucinations is usually preserved and [[REM sleep]] is usually reduced. Parkinson's disease is usually associated with a degraded [[substantia nigra]] pars compacta, but recent evidence suggests that PD affects a number of sites in the brain. Some places of noted degradation include the median raphe nuclei, the noradrenergic parts of the locus coeruleus and the [[cholinergic]] neurons in the [[parabrachial]] and [[pedunculopontine]] nuclei of the [[tegmentum]].<ref name=manford/>
===Migraine coma===
This type of hallucination is usually experienced during the recovery from a comatose state. The migraine coma can last for up to two days and a state of depression is sometimes [[Comorbidity|comorbid]]. The hallucinations occur during states of full consciousness and insight into the hallucinatory nature of the images is preserved. It has been noted that ataxic lesions accompany the migraine coma.<ref name=manford/>
===Charles Bonnet syndrome===
[[Charles Bonnet syndrome]] is the name given to visual hallucinations experienced by blind patients. The hallucinations can usually be dispersed by opening or closing the eyelids until the visual images disappear. The hallucinations usually occur during the morning or evening, but are not dependent on low light conditions. These prolonged hallucinations usually do not disturb the patients very much as they are aware that they are hallucinating.<ref name=manford/>
===Focal epilepsy===
The visual hallucinations from focal epilepsy are characterized by being brief, and stereotyped. They are usually localized to one part of the visual field and last only a few seconds. Other epileptic features may present themselves between visual episodes. Consciousness is usually impaired in some way, but nevertheless insight into the hallucination is preserved. Usually this type of focal epilepsy is caused by a lesion in the posterior temporoparietal.<ref name=manford/>
==Tactile hallucinations==
Can be associated with substance use, such as someone who feels bugs crawling on them (known as [[formication]]) after a prolonged period of [[cocaine]] use.
==Scientific explanations==
Various theories have been put forward to explain the occurrence of hallucinations. When [[psychodynamic]] ([[Freud]]ian) theories were popular in psychiatry, hallucinations were seen as a projection of unconscious wishes, thoughts and wants. As biological theories have become orthodox, hallucinations are more often thought of (by psychologists at least) as being caused by functional deficits in the [[brain]]. With reference to mental illness, the function (or dysfunction) of the [[neurotransmitter]] [[dopamine]] is thought to be particularly important.<ref>[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12505794&dopt=Abstract Kapur S. (2003)] Psychosis as a state of aberrant salience: a framework linking biology, phenomenology, and pharmacology in schizophrenia. ''American Journal of Psychiatry'', 160(1), 13-23.<br></ref>
[[Psychology|Psychological]] research has argued that hallucinations may result from biases in what are known as [[metacognition|metacognitive]] abilities.<ref>[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2404293&dopt=Abstract Bentall RP. (1990)] The illusion of reality: a review and integration of psychological research on hallucinations. ''Psychological Bulletin'', 107(1), 82-95.<br></ref> These are abilities that allow us to monitor or draw inferences from our own internal psychological states (such as [[intention]]s, [[memory|memories]], [[belief]]s and [[thought]]s). The ability to discriminate between self-generated and external sources of [[information]] is considered to be an important metacognitive skill and one which may break down to cause hallucinatory experiences. Projection of an internal state or a person's own reaction to another may arise in the form of hallucinations, especially auditory hallucinations. A few scientists have argued that such hallucinations may be the result of other conscious thoughts. A recent hypothesis that is gaining acceptance concerns the role of overactive top-down processing, or strong perceptual expectations, that can generate spontaneous perceptual output (that is, hallucination).<ref>[http://www.ncbi.nlm.nih.gov/pubmed/10932478?ordinalpos=2&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum Grossberg S. 2000]How hallucinations may arise from brain mechanisms of learning, attention, and volition. J Int Neuropsychol Soc. 2000 Jul;6(5):583-92.br></ref>
==Stages of a hallucination==
#Emergence of surprising or warded-off memory or [[fantasy (psychology)|fantasy]] images <ref name=horowitz>Horowitz, Mardi J., M.D. "Hallucinations: An Information Processing Approach." In Siegel, Ronald K., Ph. D. and L. J. West, eds. ''Hallucinations: Behavior, Experience and Theory'' (1975). New York: John Wiley.</ref>
#Frequent [[reality]] checks <ref name=horowitz />
#Last vestige of [[insight (psychology)|insight]] as hallucinations become "real" <ref name=horowitz />
#Fantasy and distortion [[Form constant|elaborated upon]] and confused with actual perception <ref name=horowitz />
#Internal-external boundaries destroyed and possible [[pantheism|pantheistic]] experience <ref name=horowitz />
== In the media==
Occasionally television programs and movies let the viewer see hallucinations experienced by one of the characters.
#an episode of ''[[Casualty (TV series)|Casualty]]'' showed a patient's [[delirium tremens]] hallucination, live-acted by a tarantula.
#On the ABC show ''[[LOST]]'', John Locke sends his protégé Boone on a vision quest via a compound induced hallucination.
#In ''[[Pirates of the Caribbean: At World's End]]'', [[Jack Sparrow]] has hallucinations, seeing a crew made up entirely out of copies of himself.
#In ''[[Melrose Place]]'', Dr Kimberly Shaw saw visions of a non-existent personality constantly. This hallucination was caused by a tumor pressing against her brain.
#On ''[[Ally McBeal]]'', the [[Ally McBeal (character)|main character]] frequently has a hallucination of a [[dancing baby]], due to the fact that as she gets older, her biological clock ticks faster.
#In the TV show ''[[Scrubs (TV series)|Scrubs]]'', hallucinations of hypothetical ridiculous situations are commonplace as gags, such as JD's head blowing up.
#In the movie ''[[A Scanner Darkly]]'', the characters experience a large number of drug-induced hallucinations.
#In the movie ''[[Dead Man's Shoes]]'' the main character spends all his time with a man who is discovered to be a hallucination of his dead brother. These are several examples out of many as hallucinations can add an interesting twist to a movie or show.
#One larger example is the book and movie ''[[Fight Club]]'', where the entire plot line is based on a hallucination of the main character, due to depression, sleep deprivation, and possibly insanity.
#Numerous examples have appeared in ''[[House (TV series)|House]]'' .
#In the movie ''[[A Beautiful Mind (film)|A Beautiful Mind]]'', mathematician John Nash has hallucinations due to ''[[schizophrenia]]''.
== See also ==
* [[Apparitional experience]]
* [[Closed-eye hallucination]]
* [[Delusion]]
* [[Dimethyltryptamine]]
* [[Dream]]
* [[Focal seizures]]
* [[Folie à deux]]
* [[Form constant]]
* [[Hallucinations in the sane]]
* [[Illusion]]
* [[Imaginary friend]]
* [[Phantom eye syndrome]]
* [[Psychedelics, dissociatives and deliriants|Hallucinogenic drug]]
* [[Psychosis]]
* [[Simulated reality]]
== External links ==
*[http://www.intervoiceonline.org/ INTERVOICE Online, website of the international hearing voices movement]
*[http://www.hearing-voices.org/ Hearing Voices Network]
*[http://www.psychanalyse-paris.com/843-Anthropology-and.html "Anthropology and Hallucinations"], chapter from ''The Making of Religion''
*[http://www.mind.org.uk/Information/Booklets/Other/The+voice+inside.htm?wbc_purpose=Basic "The voice inside: A practical guide to coping with hearing voices"]
== Further reading==
*Johnson, Fred H. (1978). ''The Anatomy of Hallucinations''. Nelson-Hall.
*Slade, P.D. and Bentall, R.P. (1988). ''Sensory Deception: a scientific analysis of hallucination''. London: Croom Helm.
*Aleman, A. and Larøi, F. (2008).''Hallucinations: the science of idiosyncratic perception''. Washington, DC: APA Books. http://books.apa.org/books.cfm?id=4318044
== References ==
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[[Category:Psychedelics, dissociatives and deliriants]]
[[Category:Psychosis]]
[[Category:Medical signs]]
[[Category:Symptoms]]
[[cs:Halucinace]]
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