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Encyclopedia > Hallucination

A hallucination is a perception in the absence of a stimulus that the person may or may not believe is real. Hallucinations may occur in any sensory modality—visual, auditory, olfactory, gustatory, tactile, proprioceptive, equilibrioceptive, nociceptive, thermoceptive. Hallucinations are different from illusions. In an illusory experience, a genuine sensation is attributed to an incorrect cause, misinterpreting a coat hanging on a door to be an intruder or thinking there is water on a hot road, due to the heat rising from the road. A delusional perception is where a genuine perception (ie. correctly sensed and interpreted) is given some additional (and typically bizarre) significance. Hypnagogic hallucinations and hypnopompic hallucinations 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 drug use (particularly hallucinogenic drugs), sleep deprivation, psychosis or neurological illness. In physiology, a stimulus is a detectable change in the internal or external environment. ... The visual system is the part of the nervous system which allows organisms to see. ... The auditory system is the sensory system for the sense of hearing. ... Olfaction (also known as olfactics) refers to the sense of smell. ... For the social and aesthetic aspects of taste, see taste (sociology). ... This article or section does not cite its references or sources. ... // Proprioception (PRO-pree-o-SEP-shun (IPA pronunciation: ); from Latin proprius, meaning ones own and perception) is the sense of the relative position of neighbouring parts of the body. ... This article or section does not adequately cite its references or sources. ... Pain is both a sensory and emotional experience, generally associated tissue damage, or inflammation. ... Thermoception or thermoreception is the sense by which an organism perceives temperature. ... Hypnogogia, also spelled Hypnagogia, is the name of an experience a person can go through when falling asleep. ... Hypnopompia is an experience a person can go through while waking from sleep. ... An assortment of psychoactive drugs A psychoactive drug or psychotropic substance is a chemical substance that acts primarily upon the central nervous system where it alters brain function, resulting in temporary changes in perception, mood, consciousness and behavior. ... The general group of pharmacological agents commonly known as hallucinogens can be divided into three broad categories: psychedelics, dissociatives, and deliriants. ... Sleep deprivation is a general lack of the necessary amount of sleep. ... Neurology is a branch of medicine dealing with disorders of the central and peripheral nervous systems. ...



Studies have now shown hallucinatory experiences take place across the world. Previous studies, one as early as 1894,[1] have reported that approximately 10% of the population experience hallucinations. A recent survey of over 9,000 people[2] 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. Olfaction, the sense of smell, is the detection of chemicals dissolved in air (or, by animals that breathe water, in water). ... Taste is one of the most common and fundamental of the senses in life on Earth. ...

Auditory Hallucinations

Auditory hallucinations, particularly of one or more talking voices, are particularly associated with 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.[3] 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. This can be caused by lesions on the brain stem, occurring most often from strokes, but also tumors, sencephalitis, or abscesses.[4] Recent reports have also mentioned that it is possible to get musical hallucinations from listening to music for long periods of time. This article is about audible acoustic waves. ... Psychosis is a generic psychiatric term for a mental state often described as involving a loss of contact with reality. Stedmans Medical Dictionary defines psychosis as a severe mental disorder, with or without organic damage, characterized by derangement of personality and loss of contact with reality and causing deterioration... A mental illness or mental disorder refers to one of many mental health conditions characterized by distress, impaired cognitive functioning, atypical behavior, emotional dysregulation, and/or maladaptive behavior. ... Hearing Voices Movement is a philosophical trend in how people who hear voices are viewed. ... A lesion is a non-specific term referring to abnormal tissue in the body. ... The brain stem is the lower part of the brain, adjoining and structurally continuous with the spinal cord. ... The Strokes are an American rock and roll band who formed in New York City and gained fame for their live shows. ... Tumor (American English) or tumour (British English) originally means swelling, and is sometimes still used with that meaning. ... An abscess is a collection of pus collected in a cavity formed by the tissue on the basis of an infectious process (usually caused by bacteria or parasites) or other foreign materials (e. ...

Visual Hallucinations

Hypnagogic Hallucination

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 non-narcoleptics. Hypnagogic hallucinations are sometimes associated with brainstem abnormalities, but this is rare.[5] For other uses, see Narcolepsy (disambiguation). ...

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 polymodal.[5] The term peduncle has several meanings: In botany, a Peduncle (botany) is a flower stalk, or stem. ... For other uses, see Pons (disambiguation). ... The brain stem is the lower part of the brain, adjoining and structurally continuous with the spinal cord. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...

Delirium Tremens

One of the most enigmatic forms of visual hallucinations are the highly variable, possibly polymodal Delirium Tremens, which is a form of withdrawal from alcohol in people with late-stage alcoholism. As the name suggests, the subject is usually 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.[5] For the beer, see Delirium Tremens (beer). ... Withdrawal, also known as withdrawal syndrome, refers to the characteristic signs and symptoms that appear when a drug that causes physical dependence is regularly used for a long time and then suddenly discontinued or decreased in dosage. ... Alcoholism is the consumption of, or preoccupation with, alcoholic beverages to the extent that this behavior interferes with the drinkers normal personal, family, social, or work life, and may lead to physical or mental harm. ... Polysomnographic record of REM Sleep. ...

Parkinson's disease and Lewy body Dementia

Parkinson's disease is linked with 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[6] 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.[5] Dementia with Lewy bodies is the second most frequent cause of hospitalization for dementia, after Alzheimers disease. ... Rapid eye movement (REM) is the stage of sleep during which the most vivid (though not all) dreams occur. ... The substantia nigra, (Latin for black substance, Soemering) or locus niger is a heterogeneous portion of the midbrain, separating the pes (foot) from the tegmentum (covering), and a major element of the basal ganglia system. ... A synapse is cholinergic if it uses acetylcholine as its neurotransmitter. ... The midbrain tegmentum is part of the midbrain extending from the substantia nigra to the cerebral aqueduct. ...

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 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.[5]

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.[5] Charles Bonnet syndrome (CBS) is named after the Swiss naturalist Charles Bonnet. ...

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.[5]

Tactile Hallucinations

Can be associated with substance use, such as someone who feels bugs crawling on them after a prolonged period of cocaine use.

Scientific explanations

Various theories have been put forward to explain the occurrence of hallucinations. When psychodynamic (Freudian) 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 psychiatrists 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.[7] Psychological research has argued that hallucinations may result from biases in what are known as metacognitive abilities.[8] These are abilities that allow us to monitor or draw inferences from our own internal psychological states (such as intentions, memories, beliefs and thoughts). 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. Psychodynamic psychotherapy is a type of psychotherapy, usually meeting about once or twice a week. ... Sigmund Freud His famous couch Sigmund Freud (May 6, 1856 - September 23, 1939) was an Austrian neurologist and the founder of the psychoanalytic school of psychology, a movement that popularized the theory that unconscious motives control much behavior. ... The human brain In animals, the brain (enkephalos) (Greek for in the skull), is the control center of the central nervous system, responsible for behavior. ... Chemical structure of D-aspartic acid, a common amino acid neurotransmitter. ... For other uses, see Dopamine (disambiguation). ... Psychological science redirects here. ... Metacognition refers to thinking about cognition (memory, perception, calculation, association, etc. ... An agents intention in performing an action is their specific purpose in doing so, the end or goal they aim at, or intend to accomplish. ... For other uses, see Memory (disambiguation). ... For other uses, see Believe. ... Personification of thought (Greek Εννοια) in Celsus Library in Ephesos, Turkey Thought or thinking is a mental process which allows beings to model the world, and so to deal with it effectively according to their goals, plans, ends and desires. ... The ASCII codes for the word Wikipedia represented in binary, the numeral system most commonly used for encoding computer information. ...

In the Media

Occasionally television programs and movies let the viewer see hallucinations experienced by one of the characters. For example, an episode of 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. Also in Pirates of the Caribbean: At World's End, Jack Sparrow has hallucinations, seeing a crew made up entirely out of copies of himself. Another case occurs in Melrose Place, when Dr Kimberely Shaw saw visions of a non-existent personality constantly. This hallucination was caused by a tumor pressing against her brain. On Ally McBeal, the 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 movie A Scanner Darkly, the characters experience a large amount of drug induced hallucinations. 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. These are several examples out of millions, because hallucinations are always an interesting twist to any movie or show. Casualty is the longest running emergency medical drama series in the world[1], first broadcast in 1986 and transmitted in the UK on BBC One (with repeats on UKTV Gold). ... For the beer, see Delirium Tremens (beer). ... For other uses, see Tarantula (disambiguation). ... Look up lost in Wiktionary, the free dictionary. ... Jack Sparrow is a fictional character from the Pirates of the Caribbean universe who is portrayed by Johnny Depp. ... Melrose Place is an American primetime soap opera that ran between 1992 and 1999, created by Darren Star for the FOX network. ... For the character, see Ally McBeal (character). ... Callista Flockhart as Ally Mcbeal Ally McBeal is the central character in the Fox Television show Ally McBeal. ... The Dancing Baby, also known as Baby Cha-Cha, refers to a 3D character and 3D-rendered animation of a baby dancing for several seconds. ... A Scanner Darkly is a 1977 science fiction novel by Philip K. Dick. ... Fight Club[1] (1996) is the first published novel by American author Chuck Palahniuk. ...

See also

This article belongs in one or more categories. ... Charles Bonnet syndrome (CBS) is named after the Swiss naturalist Charles Bonnet. ... This article or section does not cite its references or sources. ... A delusion is commonly defined as a fixed false belief and is used in everyday language to describe a belief that is either false, fanciful or derived from deception. ... Dimethyltryptamine (DMT), also known as N,N-dimethyltryptamine, is a psychedelic tryptamine. ... For other uses, see Dream (disambiguation). ... Focal seizures (also called partial seizures) are seizures which are characterized by: preserved consciousness in simple focal seizures impaired consciousness (dream-like) in complex focal seizures experience of unusual feelings or sensations sudden and inexplainable feelings of joy, anger, sadness, or nausea altered sense of hearing, smelling, tasting, seeing, or... Folie à deux (literally, a madness shared by two) is a rare psychiatric syndrome in which a symptom of psychosis (particularly a paranoid or delusional belief) is transmitted from one individual to another. ... A representation of a form constant. ... An hallucination may occur to a normal person in state of good mental and physical health, even in the apparent absence of a transient trigger factor such as fatigue, intoxication or sensory deprivation. ... Hearing Voices Movement is a philosophical trend in how people who hear voices are viewed. ... For other uses, see illusion (disambiguation). ... For other uses, see Imaginary Friend. ... The phantom eye syndrome refers to phantom phenomena, such as phantom pain in the eye and visual hallucinations, after the removal of an eye (enucleation, evisceration). ... The general group of pharmacological agents commonly known as hallucinogens can be divided into three broad categories: psychedelics, dissociatives, and deliriants. ... Psychosis is a generic psychiatric term for a mental state often described as involving a loss of contact with reality. Stedmans Medical Dictionary defines psychosis as a severe mental disorder, with or without organic damage, characterized by derangement of personality and loss of contact with reality and causing deterioration... Binomial name Epling & Játiva[1] Salvia divinorum, also known as Diviners Sage,[2] Magic Mint,[2] María Pastora,[3] Sage of the Seers, or simply Salvia (although the genus name is shared among many plants), is a powerful psychoactive plant, a member of the sage genus and... Simulated reality is the idea that reality could be simulated — often computer-simulated — to a degree indistinguishable from true reality. ... The Tetris effect is the ability of any activity to which people devote sufficient time and attention to begin to dominate their thoughts, mental images, and dreams. ...

External links

  • INTERVOICE Online, website of the international hearing voices movement
  • Hearing Voices Network
  • Visual hallucinations during migraine
  • "Anthropology and Hallucinations", chapter from The Making of Religion
  • "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.


  1. ^ 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.
  2. ^ Ohayon MM. (2000) Prevalence of hallucinations and their pathological associations in the general population. Psychiatry Research, 97(2-3), 153-64.
  3. ^ Thompson, Andrea (September 15, 2006). Hearing Voices: Some People Like It. LiveScience.com. Retrieved on 2006-11-25.
  4. ^ Rare Hallucinations Make Music In The Mind. ScienceDaily.com (August 9, 2000). Retrieved on 2006-12-31.
  5. ^ a b c d e f g Manford and Andermann (1998) Complex visual hallucinations. Clinical and Neurobiological insightsBrain, 121(10), 1819-1840.
  6. ^ Mark Derr (2006) Marilyn and Me, "The New York Times" Feb. 14th, 2006
  7. ^ 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.
  8. ^ Bentall RP. (1990) The illusion of reality: a review and integration of psychological research on hallucinations. Psychological Bulletin, 107(1), 82-95.

  Results from FactBites:
Hallucination definition - Mental Health Disorders on MedicineNet.com (0 words)
A hypnagogic hallucination is a vivid dreamlike hallucination at the onset of sleep.
Hypnopompic hallucination is a vivid dreamlike hallucination on awakening.
Kinesthetic hallucination is an hallucination involving the sense of bodily movement.
  More results at FactBites »



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