Hallucination
Encyclopedia
A hallucination, in the broadest sense of the word, is a perception
in the absence of a stimulus
. In a stricter sense, hallucinations are defined as perceptions in a conscious and awake state in the absence of external stimuli which have qualities of real perception, in that they are vivid, substantial, and located in external objective space. The latter definition distinguishes hallucinations from the related phenomena of dream
ing, which does not involve wakefulness; illusion
, which involves distorted or misinterpreted real perception; imagery, which does not mimic real perception and is under voluntary control; and pseudohallucination
, which does not mimic real perception, but is not under voluntary control.
Hallucinations also differ from "delusion
al perceptions", in which a correctly sensed and interpreted stimulus (i.e. a real perception) is given some additional (and typically bizarre) significance.
Hallucinations can occur in any sensory modality — visual
, auditory
, olfactory
, gustatory
, tactile, proprioceptive
, equilibrioceptive
, nociceptive
, thermoceptive
and chronoceptive
.
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/or voices.
Auditory hallucinations are very common in paranoid schizophrenia. They may be benevolent (telling the patient good things about themselves) or malicious, cursing the patient etc. Auditory hallucinations of the malicious type are frequently heard like people talking about the patient behind their back. Like auditory hallucinations, the source of their visual counterpart can also be behind the patient's back. Their visual counterpart is the feeling of being looked-stared at, usually with malicious intent. Frequently, auditory hallucinations and their visual counterpart are experienced by the patient together.
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 can be associated with drug
use (particularly deliriant
s), sleep deprivation
, psychosis
, neurological disorder
s, and delirium tremens
.
Sometimes internal imagery can overwhelm the sensory input from external stimuli when sharing neural pathways, or if indistinct stimuli is perceived and manipulated to match one's expectations or beliefs, especially about the environment. This can result in a hallucination.
hallucinations (also known as paracusia), are the perception of sound without outside stimulus. Auditory hallucinations can be divided into two categories: elementary and complex. Elementary hallucinations are the perception of sounds such as hissing, whistling, an extended tone, and more. In many cases, tinnitus is an elementary auditory hallucination. However, some people who experience certain types of tinnitus, especially pulsatile tinnitus, are actually hearing the blood rushing through vessels near the ear. Because the auditory stimulus is present in this situation, it does not qualify as a hallucination.
Complex hallucinations are those of voices, music, or other sounds which may or may not be clear, may be familiar or completely unfamiliar, and friendly or aggressive, among other possibilities. Hallucinations of one or more talking voices, are particularly associated with psychotic
disorders such as schizophrenia
, and hold special significance in diagnosing these conditions. However, many people not suffering from diagnosable mental illness
may sometimes hear voices as well. One important example to consider when forming a differential diagnosis for a patient with paracusia is lateral temporal lobe epilepsy
. Despite the tendency to associate hearing voices, or otherwise hallucinating, and psychosis
with schizophrenia or other psychiatric illnesses, it is crucial to take into consideration that even if a person does exhibit psychotic features, they do not necessarily suffer from a psychiatric disorder on its own. Disorders such as Wilson's disease
, various endocrinological disorders, numerous metabolic disturbances, multiple sclerosis
, systemic lupus erythematosis, porphyria
, sarcoidosis
, and many others can present with psychosis.
Musical hallucinations are also relatively common in terms of complex auditory hallucinations and may be the result of a wide range of causes ranging from hearing-loss (such as in musical ear syndrome
, the auditory version of Charles Bonnet syndrome
), lateral temporal lobe epilepsy, arteriovenous malformation, stroke, lesion
, abscess
, or tumor.
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.
. People experiencing command hallucinations may or may not comply with the hallucinated commands, depending on circumstances. Compliance is more common for non-violent commands.
is the phenomenon of smelling odor
s that aren't really present. The most common odors are unpleasant smells such as rotting flesh, vomit, urine, feces, smoke, or others. Phantosmia often results from damage to the nervous tissue
in the olfactory system. The damage can be caused by viral infection, brain tumor
, trauma
, surgery
, and possibly exposure to toxin
s or drug
s. Phantosmia can also be induced by epilepsy
affecting the olfactory cortex and is also thought to possibly have psychiatric origins. Phantosmia is different from parosmia
, in which a smell is actually present, but perceived differently from its usual smell.
Olfactory hallucinations can also appear in some cases of associative imagination, for example, while watching a romance movie, where the man gifts roses to the woman, the viewer senses the roses' odor (which in fact does not exist).
Olfactory hallucinations have also been reported in migraine, although the frequency of such hallucinations is unclear.
, is the sensation of insects crawling underneath the skin and is frequently associated with prolonged cocaine
or amphetamine
use or with withdrawal from alcohol
or benzodiazepines. However, formication may also be the result of normal hormonal changes such as menopause
, or disorders such as peripheral neuropathy
, high fevers, Lyme disease
, skin cancer
, and more.
, especially temporal lobe epilepsy
. The regions of the brain responsible for gustatory hallucination in this case are the insula
and the superior bank of the sylvian fissure.
. Hypnagogic hallucinations are sometimes associated with brainstem abnormalities, but this is rare.
, which is a neural tract running to and from the pons
on the brain stem
. These hallucinations usually occur in the evenings, but not during drowsiness, as in the case of hypnagogic hallucination. The subject is usually fully conscious and then 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.
. Individuals suffering from delirium 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 rapid eye movement sleep.
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 hallucination may begin with illusions 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
.
. 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.
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. A differential diagnosis are opthalmopathic hallucinations.
differ depending on the region of the brain where the seizure occurs. For example, visual hallucinations during occipital lobe
seizures are typically visions of brightly colored, geometric shapes that may move across the visual field
, multiply, or form concentric rings and generally persist from a few seconds to a few minutes. They are usually unilateral and localized to one part of the visual field on the ipsilateral side of the seizure focus, typically the temporal field. However, unilateral visions moving horizontally across the visual field
begin on the contralateral side and move towards the ipsilateral side.
Temporal lobe seizures
, on the other hand, can produce complex visual hallucinations of people, scenes, animals, and more as well as distortions of visual perception
. Complex hallucinations may appear real or unreal, may or may not be distorted with respect to size, and may seem disturbing or affable, among other variables. One rare but notable type of hallucination is heautoscopy
, a hallucination of a mirror image of one's self. These "other selves" may be perfectly still or performing complex tasks, may be an image of a younger self or the present self, and tend to be only briefly present. Complex hallucinations are a relatively uncommon finding in temporal lobe epilepsy patients. Rarely, they may occur during occipital focal seizures or in parietal lobe
seizures.
Distortions in visual perception during a temporal lobe seizure may include size distortion (micropsia
or macropsia
), distorted perception of movement (where moving objects may appear to be moving very slowly or to be perfectly still), a sense that surfaces such as ceilings and even entire horizons are moving farther away in a fashion similar to the dolly zoom effect, and other illusions. Even when consciousness is impaired, insight into the hallucination or illusion is typically preserved.
.
or DMT
.
. With reference to mental illness, the function (or dysfunction) of the neurotransmitters glutamate and dopamine
are thought to be particularly important. The Freudian interpretation may have an aspect of truth, as the biological hypothesis explains the physical interactions in the brain, while the Freudian deals with the origin of the theme of the hallucination.
Psychological
research has argued that hallucinations may result from biases in what are known as metacognitive
abilities.
These are abilities that allow us to monitor or draw inferences from our own internal psychological states (such as intention
s, memories
, belief
s and thought
s). The ability to discriminate between internal (self-generated) and external (stimuli) sources of information
is considered to be an important metacognitive skill, but one which may break down to cause hallucinatory experiences. Projection of an internal state (or a person's own reaction to another's) may arise in the form of hallucinations, especially auditory hallucinations. 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).
and atypical antipsychotic
medication may also be utilized to treat the illness if the symptoms are severe and cause significant distress. For other causes of hallucinations there is no factual evidence to support any one treatment is scientifically tested and proven. However, abstaining from hallucinogenic drugs, managing stress levels, living healthily, and getting plenty of sleep can help reduce the prevalence of hallucinations. In all cases of hallucinations, medical attention should be sought out and informed of one's specific symptoms.
Perception
Perception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs...
in the absence of a stimulus
Stimulus (physiology)
In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....
. In a stricter sense, hallucinations are defined as perceptions in a conscious and awake state in the absence of external stimuli which have qualities of real perception, in that they are vivid, substantial, and located in external objective space. The latter definition distinguishes hallucinations from the related phenomena of dream
Dream
Dreams are successions of images, ideas, emotions, and sensations that occur involuntarily in the mind during certain stages of sleep. The content and purpose of dreams are not definitively understood, though they have been a topic of scientific speculation, philosophical intrigue and religious...
ing, which does not involve wakefulness; illusion
Illusion
An illusion is a distortion of the senses, revealing how the brain normally organizes and interprets sensory stimulation. While illusions distort reality, they are generally shared by most people....
, which involves distorted or misinterpreted real perception; imagery, which does not mimic real perception and is under voluntary control; and pseudohallucination
Pseudohallucination
A pseudohallucination is an involuntary sensory experience vivid enough to be regarded as a hallucination, but recognised by the patient not to be the result of external stimuli. In other words, it is a hallucination that is recognized as a hallucination, as opposed to a "normal" hallucination...
, which does not mimic real perception, but is not under voluntary control.
Hallucinations also differ from "delusion
Delusion
A delusion is a false belief held with absolute conviction despite superior evidence. Unlike hallucinations, delusions are always pathological...
al perceptions", in which a correctly sensed and interpreted stimulus (i.e. a real perception) is given some additional (and typically bizarre) significance.
Hallucinations can occur in any sensory modality — visual
Visual system
The visual system is the part of the central nervous system which enables organisms to process visual detail, as well as enabling several non-image forming photoresponse functions. It interprets information from visible light to build a representation of the surrounding world...
, auditory
Auditory system
The auditory system is the sensory system for the sense of hearing.- Outer ear :The folds of cartilage surrounding the ear canal are called the pinna...
, olfactory
Olfaction
Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...
, gustatory
Taste
Taste is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons, etc....
, tactile, proprioceptive
Proprioception
Proprioception , from Latin proprius, meaning "one's own" and perception, is the sense of the relative position of neighbouring parts of the body and strength of effort being employed in movement...
, equilibrioceptive
Equilibrioception
Equilibrioception or sense of balance is one of the physiological senses. It helps prevent humans and animals from falling over when walking or standing still. Balance is the result of a number of body systems working together: the eyes , ears and the body's sense of where it is in space ideally...
, nociceptive
Nociception
Nociception is defined as "the neural processes of encoding and processing noxious stimuli." It is the afferent activity produced in the peripheral and central nervous system by stimuli that have the potential to damage tissue...
, thermoceptive
Thermoception
Thermoception or thermoreception is the sense by which an organism perceives temperature. The details of how temperature receptors work are still being investigated. Ciliopathy is associated with decreased ability to sense heat, thus cilia may aid in the process...
and chronoceptive
Time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....
.
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
Peripheral vision
Peripheral vision is a part of vision that occurs outside the very center of gaze. There is a broad set of non-central points in the field of view that is included in the notion of peripheral vision...
, or hearing faint noises and/or voices.
Auditory hallucinations are very common in paranoid schizophrenia. They may be benevolent (telling the patient good things about themselves) or malicious, cursing the patient etc. Auditory hallucinations of the malicious type are frequently heard like people talking about the patient behind their back. Like auditory hallucinations, the source of their visual counterpart can also be behind the patient's back. Their visual counterpart is the feeling of being looked-stared at, usually with malicious intent. Frequently, auditory hallucinations and their visual counterpart are experienced by the patient together.
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 can be associated with drug
Psychoactive drug
A psychoactive drug, psychopharmaceutical, or psychotropic is a chemical substance that crosses the blood–brain barrier and acts primarily upon the central nervous system where it affects brain function, resulting in changes in perception, mood, consciousness, cognition, and behavior...
use (particularly deliriant
Deliriant
The deliriants are a special class of acetylcholine-inhibitor hallucinogen. The term was introduced by David F. Duncan and Robert S...
s), sleep deprivation
Sleep deprivation
Sleep deprivation is the condition of not having enough sleep; it can be either chronic or acute. A chronic sleep-restricted state can cause fatigue, daytime sleepiness, clumsiness and weight loss or weight gain. It adversely affects the brain and cognitive function. Few studies have compared the...
, psychosis
Psychosis
Psychosis means abnormal condition of the mind, and is a generic psychiatric term for a mental state often described as involving a "loss of contact with reality"...
, neurological disorder
Neurological disorder
A neurological disorder is a disorder of the body's nervous system. Structural, biochemical or electrical abnormalities in the brain, spinal cord, or in the nerves leading to or from them, can result in symptoms such as paralysis, muscle weakness, poor coordination, loss of sensation, seizures,...
s, and delirium tremens
Delirium tremens
Delirium tremens is an acute episode of delirium that is usually caused by withdrawal from alcohol, first described in 1813...
.
Classification
Hallucinations may be manifested in a variety of forms. Various forms of hallucinations affect different senses, sometimes occurring simultaneously, creating multiple sensory hallucinations for those experiencing them.Visual
The most common modality referred to when people speak of hallucinations. These include the phenomena of seeing things which are not present or visual perception which does not reconcile with the consensus reality. There are many different causes, which have been classed as psychophysiologic (a disturbance of brain structure), psychobiochemical (a disturbance of neurotransmitters), and psychological (e.g. meaningful experiences consciousness). Numerous disorders can involve visual hallucinations, ranging from psychotic disorders to dementia to migraine, but experiencing visual hallucinations does not in itself mean there is necessarily a disorder. Visual hallucinations are associated with organic disorders of the brain and with drug and alcohol related illness.Sometimes internal imagery can overwhelm the sensory input from external stimuli when sharing neural pathways, or if indistinct stimuli is perceived and manipulated to match one's expectations or beliefs, especially about the environment. This can result in a hallucination.
Auditory
AuditorySound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
hallucinations (also known as paracusia), are the perception of sound without outside stimulus. Auditory hallucinations can be divided into two categories: elementary and complex. Elementary hallucinations are the perception of sounds such as hissing, whistling, an extended tone, and more. In many cases, tinnitus is an elementary auditory hallucination. However, some people who experience certain types of tinnitus, especially pulsatile tinnitus, are actually hearing the blood rushing through vessels near the ear. Because the auditory stimulus is present in this situation, it does not qualify as a hallucination.
Complex hallucinations are those of voices, music, or other sounds which may or may not be clear, may be familiar or completely unfamiliar, and friendly or aggressive, among other possibilities. Hallucinations of one or more talking voices, are particularly associated with psychotic
Psychosis
Psychosis means abnormal condition of the mind, and is a generic psychiatric term for a mental state often described as involving a "loss of contact with reality"...
disorders such as schizophrenia
Schizophrenia
Schizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...
, and hold special significance in diagnosing these conditions. However, many people not suffering from diagnosable mental illness
Mental illness
A mental disorder or mental illness is a psychological or behavioral pattern generally associated with subjective distress or disability that occurs in an individual, and which is not a part of normal development or culture. Such a disorder may consist of a combination of affective, behavioural,...
may sometimes hear voices as well. One important example to consider when forming a differential diagnosis for a patient with paracusia is lateral temporal lobe epilepsy
Temporal lobe epilepsy
Temporal lobe epilepsy a.k.a. Psychomotor epilepsy, is a form of focal epilepsy, a chronic neurological condition characterized by recurrent seizures. Over 40 types of epilepsies are known. They fall into two main categories: partial-onset epilepsies and generalized-onset epilepsies...
. Despite the tendency to associate hearing voices, or otherwise hallucinating, and psychosis
Psychosis
Psychosis means abnormal condition of the mind, and is a generic psychiatric term for a mental state often described as involving a "loss of contact with reality"...
with schizophrenia or other psychiatric illnesses, it is crucial to take into consideration that even if a person does exhibit psychotic features, they do not necessarily suffer from a psychiatric disorder on its own. Disorders such as Wilson's disease
Wilson's disease
Wilson's disease or hepatolenticular degeneration is an autosomal recessive genetic disorder in which copper accumulates in tissues; this manifests as neurological or psychiatric symptoms and liver disease...
, various endocrinological disorders, numerous metabolic disturbances, multiple sclerosis
Multiple sclerosis
Multiple sclerosis is an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms...
, systemic lupus erythematosis, porphyria
Porphyria
Porphyrias are a group of inherited or acquired disorders of certain enzymes in the heme bio-synthetic pathway . They are broadly classified as acute porphyrias and cutaneous porphyrias, based on the site of the overproduction and accumulation of the porphyrins...
, sarcoidosis
Sarcoidosis
Sarcoidosis , also called sarcoid, Besnier-Boeck disease or Besnier-Boeck-Schaumann disease, is a disease in which abnormal collections of chronic inflammatory cells form as nodules in multiple organs. The cause of sarcoidosis is unknown...
, and many others can present with psychosis.
Musical hallucinations are also relatively common in terms of complex auditory hallucinations and may be the result of a wide range of causes ranging from hearing-loss (such as in musical ear syndrome
Musical ear syndrome
Musical ear syndrome describes a condition seen in people who have hearing loss and subsequently develop auditory hallucinations. It is comparable to Charles Bonnet syndrome and some have suggested this phenomenon could be included under this diagnosis.The occurrence of MES has been suggested to...
, the auditory version of Charles Bonnet syndrome
Charles Bonnet syndrome
Charles Bonnet syndrome is a condition that causes patients with visual loss to have complex visual hallucinations, first described by Charles Bonnet in 1760 and first introduced into English-speaking psychiatry in 1982.-Characteristics:...
), lateral temporal lobe epilepsy, arteriovenous malformation, stroke, lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
, abscess
Abscess
An abscess is a collection of pus that has accumulated in a cavity formed by the tissue in which the pus resides due to an infectious process or other foreign materials...
, or tumor.
The Hearing Voices Movement
Hearing Voices Movement
Hearing Voices Movement is a philosophical trend in how people who hear voices are viewed. It was begun by Marius Romme, a professor of social psychiatry at the University of Limburg in Maastricht, the Netherlands; and Sandra Escher, a science journalist, who began this work after being challenged...
is a support and advocacy group for people who hallucinate voices, but do not otherwise show signs of mental illness or impairment.
Command hallucinations
Command hallucinations are hallucinations in the form of commands. The contents of the hallucinations can range from the innocuous to commands to cause harm to the self or others. Command hallucinations are often associated with schizophreniaSchizophrenia
Schizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...
. People experiencing command hallucinations may or may not comply with the hallucinated commands, depending on circumstances. Compliance is more common for non-violent commands.
Olfactory
PhantosmiaPhantosmia
Phantosmia, or olfactory hallucinations, involves smelling odors that are not derived from any physical stimulus. These phantom odors can range from rotting flesh to a spring meadow, though most cases report unpleasant aromas...
is the phenomenon of smelling odor
Odor
An odor or odour is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans or other animals perceive by the sense of olfaction. Odors are also commonly called scents, which can refer to both pleasant and unpleasant odors...
s that aren't really present. The most common odors are unpleasant smells such as rotting flesh, vomit, urine, feces, smoke, or others. Phantosmia often results from damage to the nervous tissue
Nervous tissue
Nervous tissue is one of four major classes of vertebrate tissue.Nervous tissue is the main component of the nervous system - the brain, spinal cord, and nerves-which regulates and controls body functions...
in the olfactory system. The damage can be caused by viral infection, brain tumor
Brain tumor
A brain tumor is an intracranial solid neoplasm, a tumor within the brain or the central spinal canal.Brain tumors include all tumors inside the cranium or in the central spinal canal...
, trauma
Physical trauma
Trauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...
, surgery
Surgery
Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...
, and possibly exposure to toxin
Toxin
A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...
s or drug
Drug
A drug, broadly speaking, is any substance that, when absorbed into the body of a living organism, alters normal bodily function. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage.In pharmacology, a...
s. Phantosmia can also be induced by epilepsy
Epilepsy
Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...
affecting the olfactory cortex and is also thought to possibly have psychiatric origins. Phantosmia is different from parosmia
Parosmia
Parosmia, also known as troposmia or cacosmia, is an olfactory dysfunction that is characterized by the inability of the brain to properly identify an odor’s “natural” smell....
, in which a smell is actually present, but perceived differently from its usual smell.
Olfactory hallucinations can also appear in some cases of associative imagination, for example, while watching a romance movie, where the man gifts roses to the woman, the viewer senses the roses' odor (which in fact does not exist).
Olfactory hallucinations have also been reported in migraine, although the frequency of such hallucinations is unclear.
Tactile hallucinations
Tactile hallucinations are the illusion of tactile sensory input, simulating various types of pressure to the skin or other organs. One subtype of tactile hallucination, formicationFormication
Formication is the medical term for a sensation that resembles that of insects crawling on the skin. It is one specific form of a set of sensations known as paresthesia, which also include the more common prickling, tingling sensation of "pins and needles"...
, is the sensation of insects crawling underneath the skin and is frequently associated with prolonged cocaine
Cocaine
Cocaine is a crystalline tropane alkaloid that is obtained from the leaves of the coca plant. The name comes from "coca" in addition to the alkaloid suffix -ine, forming cocaine. It is a stimulant of the central nervous system, an appetite suppressant, and a topical anesthetic...
or amphetamine
Amphetamine
Amphetamine or amfetamine is a psychostimulant drug of the phenethylamine class which produces increased wakefulness and focus in association with decreased fatigue and appetite.Brand names of medications that contain, or metabolize into, amphetamine include Adderall, Dexedrine, Dextrostat,...
use or with withdrawal from alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
or benzodiazepines. However, formication may also be the result of normal hormonal changes such as menopause
Menopause
Menopause is a term used to describe the permanent cessation of the primary functions of the human ovaries: the ripening and release of ova and the release of hormones that cause both the creation of the uterine lining and the subsequent shedding of the uterine lining...
, or disorders such as peripheral neuropathy
Peripheral neuropathy
Peripheral neuropathy is the term for damage to nerves of the peripheral nervous system, which may be caused either by diseases of or trauma to the nerve or the side-effects of systemic illness....
, high fevers, Lyme disease
Lyme disease
Lyme disease, or Lyme borreliosis, is an emerging infectious disease caused by at least three species of bacteria belonging to the genus Borrelia. Borrelia burgdorferi sensu stricto is the main cause of Lyme disease in the United States, whereas Borrelia afzelii and Borrelia garinii cause most...
, skin cancer
Skin cancer
Skin neoplasms are skin growths with differing causes and varying degrees of malignancy. The three most common malignant skin cancers are basal cell cancer, squamous cell cancer, and melanoma, each of which is named after the type of skin cell from which it arises...
, and more.
Gustatory
This type of hallucination is the perception of taste without a stimulus. These hallucinations, which are typically strange or unpleasant, are relatively common among individuals who have certain types of focal epilepsyEpilepsy
Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...
, especially temporal lobe epilepsy
Temporal lobe epilepsy
Temporal lobe epilepsy a.k.a. Psychomotor epilepsy, is a form of focal epilepsy, a chronic neurological condition characterized by recurrent seizures. Over 40 types of epilepsies are known. They fall into two main categories: partial-onset epilepsies and generalized-onset epilepsies...
. The regions of the brain responsible for gustatory hallucination in this case are the insula
Insula
Insula is the Latin word for "island" and may refer to:*Insular cortex, a human brain structure*Insula , an apartment building in ancient Rome that provided housing for all but the elite...
and the superior bank of the sylvian fissure.
General Somatic Sensations
General somatic sensations of a hallucinatory nature are experienced when an individual feels that his body is being mutilated i.e. twisted, torn, or disembowelled. Other reported cases are invasion by animals in the person's internal organs such as snakes in the stomach or frogs in the rectum. The general feeling that one's flesh is decomposing is also classified under this type of hallucination.Stages of a hallucination
- Emergence of surprising or warded-off memory or fantasyFantasy (psychology)Fantasy in a psychological sense is broadly used to cover two different senses, conscious and unconscious. In the unconscious sense, it is sometimes spelled "phantasy".-Conscious fantasy:...
images - Frequent realityRealityIn philosophy, reality is the state of things as they actually exist, rather than as they may appear or might be imagined. In a wider definition, reality includes everything that is and has been, whether or not it is observable or comprehensible...
checks - Last vestige of insightInsightInsight is the understanding of a specific cause and effect in a specific context. Insight can be used with several related meanings:*a piece of information...
as hallucinations become "real" - Fantasy and distortion elaborated uponForm constantA form constant is one of several geometric patterns which are recurringly observed during hallucinations and altered states of consciousness.-History:...
and confused with actual perception - Internal-external boundaries destroyed and possible pantheisticPantheismPantheism is the view that the Universe and God are identical. Pantheists thus do not believe in a personal, anthropomorphic or creator god. The word derives from the Greek meaning "all" and the Greek meaning "God". As such, Pantheism denotes the idea that "God" is best seen as a process of...
experience
Cause
Hallucinations can be caused by a number of factors.Hypnagogic hallucination
These hallucinations occur just before falling asleep, and affect a surprisingly high proportion of 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 may be associated with narcolepsyNarcolepsy
Narcolepsy is a chronic sleep disorder, or dyssomnia, characterized by excessive sleepiness and sleep attacks at inappropriate times, such as while at work. People with narcolepsy often experience disturbed nocturnal sleep and an abnormal daytime sleep pattern, which often is confused with insomnia...
. Hypnagogic hallucinations are sometimes associated with brainstem abnormalities, but this is rare.
Peduncular hallucinosis
Peduncular means pertaining to the peduncleCerebral peduncle
Mainly, the three common areas that give rise to the cerebral peduncles are the cortex, the spinal cord and the cerebellum. The cerebral peduncle, by most classifications, is everything in the mesencephalon except the tectum. The region includes the midbrain tegmentum, crus cerebri and pretectum...
, which is a neural tract running to and from the pons
Pons
The pons is a structure located on the brain stem, named after the Latin word for "bridge" or the 16th-century Italian anatomist and surgeon Costanzo Varolio . It is superior to the medulla oblongata, inferior to the midbrain, and ventral to the cerebellum. In humans and other bipeds this means it...
on the brain stem
Brain stem
In vertebrate anatomy the brainstem is the posterior part of the brain, adjoining and structurally continuous with the spinal cord. The brain stem provides the main motor and sensory innervation to the face and neck via the cranial nerves...
. These hallucinations usually occur in the evenings, but not during drowsiness, as in the case of hypnagogic hallucination. The subject is usually fully conscious and then 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.
Delirium tremens
One of the more enigmatic forms of visual hallucination is the highly variable, possibly polymodal delirium tremensDelirium tremens
Delirium tremens is an acute episode of delirium that is usually caused by withdrawal from alcohol, first described in 1813...
. Individuals suffering from delirium 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 rapid eye movement sleep.
Parkinson's disease and Lewy body dementia
Parkinson's diseaseParkinson's disease
Parkinson's disease is a degenerative disorder of the central nervous system...
is linked with Lewy body dementia
Dementia with Lewy bodies
Dementia with Lewy bodies , also known under a variety of other names including Lewy body dementia, diffuse Lewy body disease, cortical Lewy body disease, and senile dementia of Lewy type, is a type of dementia closely allied to both Alzheimers and Parkinson's Diseases...
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 hallucination may begin with illusions 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
Substantia nigra
The substantia nigra is a brain structure located in the mesencephalon that plays an important role in reward, addiction, and movement. Substantia nigra is Latin for "black substance", as parts of the substantia nigra appear darker than neighboring areas due to high levels of melanin in...
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
Cholinergic
The word choline generally refers to the various quaternary ammonium salts containing the N,N,N-trimethylethanolammonium cation. Found in most animal tissues, choline is a primary component of the neurotransmitter acetylcholine and functions with inositol as a basic constituent of lecithin...
neurons in the parabrachial and pedunculopontine nuclei of the tegmentum
Tegmentum
The tegmentum is a general area within the brainstem. It is located between the ventricular system and distinctive basal or ventral structures at each level...
.
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 comorbidComorbidity
In medicine, comorbidity is either the presence of one or more disorders in addition to a primary disease or disorder, or the effect of such additional disorders or diseases.- In medicine :...
. 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.
Charles Bonnet syndrome
Charles Bonnet syndromeCharles Bonnet syndrome
Charles Bonnet syndrome is a condition that causes patients with visual loss to have complex visual hallucinations, first described by Charles Bonnet in 1760 and first introduced into English-speaking psychiatry in 1982.-Characteristics:...
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. A differential diagnosis are opthalmopathic hallucinations.
Focal epilepsy
Visual hallucinations due to focal seizuresFocal seizures
Partial seizures are seizures which affect only a part of the brain at onset. The brain is divided into two hemispheres, each consisting of four lobes - the frontal, temporal, parietal and occipital lobes...
differ depending on the region of the brain where the seizure occurs. For example, visual hallucinations during occipital lobe
Occipital lobe
The occipital lobe is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex. The primary visual cortex is Brodmann area 17, commonly called V1...
seizures are typically visions of brightly colored, geometric shapes that may move across the visual field
Visual field
The term visual field is sometimes used as a synonym to field of view, though they do not designate the same thing. The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments", while 'field of view' "refers to the physical...
, multiply, or form concentric rings and generally persist from a few seconds to a few minutes. They are usually unilateral and localized to one part of the visual field on the ipsilateral side of the seizure focus, typically the temporal field. However, unilateral visions moving horizontally across the visual field
Visual field
The term visual field is sometimes used as a synonym to field of view, though they do not designate the same thing. The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments", while 'field of view' "refers to the physical...
begin on the contralateral side and move towards the ipsilateral side.
Temporal lobe seizures
Temporal lobe epilepsy
Temporal lobe epilepsy a.k.a. Psychomotor epilepsy, is a form of focal epilepsy, a chronic neurological condition characterized by recurrent seizures. Over 40 types of epilepsies are known. They fall into two main categories: partial-onset epilepsies and generalized-onset epilepsies...
, on the other hand, can produce complex visual hallucinations of people, scenes, animals, and more as well as distortions of visual perception
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...
. Complex hallucinations may appear real or unreal, may or may not be distorted with respect to size, and may seem disturbing or affable, among other variables. One rare but notable type of hallucination is heautoscopy
Heautoscopy
Heautoscopy is a term used in psychiatry and neurology for the reduplicative hallucination of "seeing one's own body at a distance" . It can occur as a symptom in schizophrenia and epilepsy. Heautoscopy is considered as one possible explanation for the doppelgänger phenomena....
, a hallucination of a mirror image of one's self. These "other selves" may be perfectly still or performing complex tasks, may be an image of a younger self or the present self, and tend to be only briefly present. Complex hallucinations are a relatively uncommon finding in temporal lobe epilepsy patients. Rarely, they may occur during occipital focal seizures or in parietal lobe
Parietal lobe
The parietal lobe is a part of the Brain positioned above the occipital lobe and behind the frontal lobe.The parietal lobe integrates sensory information from different modalities, particularly determining spatial sense and navigation. For example, it comprises somatosensory cortex and the...
seizures.
Distortions in visual perception during a temporal lobe seizure may include size distortion (micropsia
Micropsia
Micropsia is a condition affecting human visual perception in which objects are perceived to be smaller than they actually are. Micropsia can be caused by either optical distortion of images in the eye or by a neurological dysfunction. The condition of micropsia can be caused by more factors than...
or macropsia
Macropsia
Macropsia is a neurological condition affecting human visual perception, in which objects within an affected section of the visual field appear larger than normal, causing the subject to feel smaller. Macropsia, along with its opposite condition, micropsia, can be categorized under dysmetropsia...
), distorted perception of movement (where moving objects may appear to be moving very slowly or to be perfectly still), a sense that surfaces such as ceilings and even entire horizons are moving farther away in a fashion similar to the dolly zoom effect, and other illusions. Even when consciousness is impaired, insight into the hallucination or illusion is typically preserved.
Schizophrenic hallucination
Hallucinations caused by schizophreniaSchizophrenia
Schizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...
.
Drug-induced hallucination
Hallucinations caused by the consumption of psychoactive substances such as LSDLSD
Lysergic acid diethylamide, abbreviated LSD or LSD-25, also known as lysergide and colloquially as acid, is a semisynthetic psychedelic drug of the ergoline family, well known for its psychological effects which can include altered thinking processes, closed and open eye visuals, synaesthesia, an...
or DMT
Dimethyltryptamine
N,N-Dimethyltryptamine is a naturally occurring psychedelic compound of the tryptamine family. DMT is found in several plants, and also in trace amounts in humans and other mammals, where it is originally derived from the essential amino acid tryptophan, and ultimately produced by the enzyme INMT...
.
Sensory deprivation hallucination
Hallucinations can be caused by sense deprivation when it occurs for prolonged periods of time, and almost always occur in the modality being deprived (visual for blindfolded/darkness, auditory for muffled conditions, etc.)Pathophysiology
Various theories have been put forward to explain the occurrence of hallucinations. When psychodynamic (Freudian) theories were popular in psychology, 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 brainHuman brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
. With reference to mental illness, the function (or dysfunction) of the neurotransmitters glutamate and dopamine
Dopamine
Dopamine is a catecholamine neurotransmitter present in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this substituted phenethylamine functions as a neurotransmitter, activating the five known types of dopamine receptors—D1, D2, D3, D4, and D5—and their...
are thought to be particularly important. The Freudian interpretation may have an aspect of truth, as the biological hypothesis explains the physical interactions in the brain, while the Freudian deals with the origin of the theme of the hallucination.
Psychological
Psychology
Psychology is the study of the mind and behavior. Its immediate goal is to understand individuals and groups by both establishing general principles and researching specific cases. For many, the ultimate goal of psychology is to benefit society...
research has argued that hallucinations may result from biases in what are known as metacognitive
Metacognition
Metacognition is defined as "cognition about cognition", or "knowing about knowing." It can take many forms; it includes knowledge about when and how to use particular strategies for learning or for problem solving...
abilities.
These are abilities that allow us to monitor or draw inferences from our own internal psychological states (such as intention
Intention
Intention is an agent's specific purpose in performing an action or series of actions, the end or goal that is aimed at. Outcomes that are unanticipated or unforeseen are known as unintended consequences....
s, memories
Memory
In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....
, belief
Belief
Belief is the psychological state in which an individual holds a proposition or premise to be true.-Belief, knowledge and epistemology:The terms belief and knowledge are used differently in philosophy....
s and thought
Thought
"Thought" generally refers to any mental or intellectual activity involving an individual's subjective consciousness. It can refer either to the act of thinking or the resulting ideas or arrangements of ideas. Similar concepts include cognition, sentience, consciousness, and imagination...
s). The ability to discriminate between internal (self-generated) and external (stimuli) sources of information
Information
Information in its most restricted technical sense is a message or collection of messages that consists of an ordered sequence of symbols, or it is the meaning that can be interpreted from such a message or collection of messages. Information can be recorded or transmitted. It can be recorded as...
is considered to be an important metacognitive skill, but one which may break down to cause hallucinatory experiences. Projection of an internal state (or a person's own reaction to another's) may arise in the form of hallucinations, especially auditory hallucinations. 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).
Treatments
There are few treatments for many types of hallucinations. However, for those hallucinations caused by mental disease, a psychologist or psychiatrist should be alerted, and treatment will be based on the observations of those doctors. AntipsychoticAntipsychotic
An antipsychotic is a tranquilizing psychiatric medication primarily used to manage psychosis , particularly in schizophrenia and bipolar disorder. A first generation of antipsychotics, known as typical antipsychotics, was discovered in the 1950s...
and atypical antipsychotic
Atypical antipsychotic
The atypical antipsychotics are a group of antipsychotic tranquilizing drugs used to treat psychiatric conditions. Some atypical antipsychotics are FDA approved for use in the treatment of schizophrenia...
medication may also be utilized to treat the illness if the symptoms are severe and cause significant distress. For other causes of hallucinations there is no factual evidence to support any one treatment is scientifically tested and proven. However, abstaining from hallucinogenic drugs, managing stress levels, living healthily, and getting plenty of sleep can help reduce the prevalence of hallucinations. In all cases of hallucinations, medical attention should be sought out and informed of one's specific symptoms.
Epidemiology
One study from as early as 1895 reported that approximately 10% of the population experienced hallucinations. A 1996-1999 survey of over 13,000 people reported a much higher figure, with almost 39% of people reporting hallucinatory experiences, 27% of which were 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.See also
- Apparitional experienceApparitional experienceIn psychology and parapsychology, an apparitional experience is an anomalous, quasi-perceptual experience.It is characterized by the apparent perception of either a living being or an inanimate object without there being any material stimulus for such a perception...
- Closed-eye hallucinationClosed-eye hallucinationClosed-eye hallucinations and closed-eye visualizations are a distinct class of hallucination. These types of hallucinations generally only occur when one's eyes are closed or when one is in a darkened room. They are a form of phosphene....
- DimethyltryptamineDimethyltryptamineN,N-Dimethyltryptamine is a naturally occurring psychedelic compound of the tryptamine family. DMT is found in several plants, and also in trace amounts in humans and other mammals, where it is originally derived from the essential amino acid tryptophan, and ultimately produced by the enzyme INMT...
- Focal seizuresFocal seizuresPartial seizures are seizures which affect only a part of the brain at onset. The brain is divided into two hemispheres, each consisting of four lobes - the frontal, temporal, parietal and occipital lobes...
- Folie à deuxFolie à deux-Further reading:*Halgin, R. & Whitbourne, S. Abnormal Psychology: Clinical Perspectives on Psychological Disorders. McGraw-Hill. ISBN 0072817216...
- Hallucinations in the saneHallucinations in the saneA hallucination may occur in a person in a state of good mental and physical health, even in the apparent absence of a transient trigger factor such as fatigue, intoxication or sensory deprivation....
- Imaginary friendImaginary friendImaginary friends and imaginary companions are a psychological and social phenomenon where a friendship or other interpersonal relationship takes place in the imagination rather than external physical reality. Imaginary friends are fictional characters created for improvisational role-playing. They...
- Microwave auditory effectMicrowave auditory effectThe microwave auditory effect, also known as the microwave hearing effect or the Frey effect, consists of audible clicks induced by pulsed/modulated microwave frequencies. The clicks are generated directly inside the human head without the need of any receiving electronic device...
- Phantom eye syndromePhantom eye syndromeThe phantom eye syndrome is a phantom pain in the eye and visual hallucinations after the removal of an eye .- Symptomatology :Many patients experience one or more phantom phenomena after the removal of the eye:...
- PsychosisPsychosisPsychosis means abnormal condition of the mind, and is a generic psychiatric term for a mental state often described as involving a "loss of contact with reality"...
- Simulated realitySimulated realitySimulated reality is the proposition that reality could be simulated—perhaps by computer simulation—to a degree indistinguishable from "true" reality. It could contain conscious minds which may or may not be fully aware that they are living inside a simulation....
- Vision (spirituality)
Further reading
- Johnson FH (1978). The anatomy of hallucinations. Chicago: Nelson-Hall Co. ISBN 0-88229-155-6.
- Bentall RP, Slade PD (1988). Sensory deception: a scientific analysis of hallucination. London: Croom Helm. ISBN 0-7099-3961-2.
- Aleman A, Larøi F (2008). Hallucinations: The Science of Idiosyncratic Perception. American Psychological Association (APA). ISBN 1-4338-0311-9.
External links
- Hearing Voices Network
- "Anthropology and Hallucinations", chapter from The Making of Religion
- "The voice inside: A practical guide to coping with hearing voices"
- Psychology Terms