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August Natterer Meine Augen zur Zeit der Erscheinungen.jpg
My eyes at the moment of the apparitions by August Natterer, a German artist who created many drawings of his hallucinations
Specialty Psychiatry

A hallucination is a perception in the absence of an external stimulus that has the qualities of a real perception. Hallucinations are vivid, substantial, and are perceived to be located in external objective space. Hallucination is a combination of 2 conscious states of brain wakefulness and REM sleep. [1] They are distinguishable from several related phenomena, such as dreaming (REM sleep), which does not involve wakefulness; pseudohallucination, which does not mimic real perception, and is accurately perceived as unreal; illusion, which involves distorted or misinterpreted real perception; and mental imagery, which does not mimic real perception, and is under voluntary control. [2] Hallucinations also differ from "delusional perceptions", in which a correctly sensed and interpreted stimulus (i.e., a real perception) is given some additional significance. Many hallucinations happen also during sleep paralyses. [3]


Hallucinations can occur in any sensory modalityvisual, auditory, olfactory, gustatory, tactile, proprioceptive, equilibrioceptive, nociceptive, thermoceptive and chronoceptive. Hallucinations are referred to as multimodal if multiple sensory modalities occur. [4] [5]

A mild form of hallucination is known as a disturbance, and can occur in most of the senses above. These may be things like seeing movement in peripheral vision, or hearing faint noises or voices. Auditory hallucinations are very common in schizophrenia. They may be benevolent (telling the subject good things about themselves) or malicious, cursing the subject. 55% of auditory hallucinations are malicious in content, [6] for example, people talking about the subject, not speaking to them directly. Like auditory hallucinations, the source of the visual counterpart can also be behind the subject. This can produce a feeling of being looked or stared at, usually with malicious intent.[ citation needed ] Frequently, auditory hallucinations and their visual counterpart are experienced by the subject together. [7]

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 deliriants), sleep deprivation, psychosis, neurological disorders, and delirium tremens.

The word "hallucination" itself was introduced into the English language by the 17th-century physician Sir Thomas Browne in 1646 from the derivation of the Latin word alucinari meaning to wander in the mind. For Browne, hallucination means a sort of vision that is "depraved and receive[s] its objects erroneously". [8]


Hallucinations may be manifested in a variety of forms. [9] Various forms of hallucinations affect different senses, sometimes occurring simultaneously, creating multiple sensory hallucinations for those experiencing them.


Auditory hallucinations (also known as paracusia) [10] are the perception of sound without outside stimulus. Auditory hallucinations can be divided into elementary and complex, along with verbal and nonverbal. These hallucinations are the most common type of hallucination, with auditory verbal hallucinations being more common than nonverbal. [11] 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 it as a hallucination.

Complex hallucinations are those of voices, music, or other sounds that may or may not be clear, may or may not be familiar, and may be friendly, aggressive, or among other possibilities. A hallucination of a single individual person of one or more talking voices is particularly associated with psychotic disorders such as schizophrenia, and hold special significance in diagnosing these conditions.

In schizophrenia voices are normally perceived coming from outside the person but in dissociative disorders they are perceived as originating from within the person, commenting in their head instead of behind their back. Differential diagnosis between schizophrenia and dissociative disorders is challenging due to many overlapping symptoms, especially Schneiderian first rank symptoms such as hallucinations. [12] However, many people who do not have a diagnosable mental illness may sometimes hear voices as well. [13] 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 have a psychiatric disorder on its own. Disorders such as Wilson's disease, various endocrine diseases, numerous metabolic disturbances, multiple sclerosis, systemic lupus erythematosus, 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, [14] arteriovenous malformation, [15] stroke, lesion, abscess, or tumor. [16]

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.

High caffeine consumption has been linked to an increase in likelihood of one experiencing auditory hallucinations. A study conducted by the La Trobe University School of Psychological Sciences revealed that as few as five cups of coffee a day (approximately 500 mg of caffeine) could trigger the phenomenon. [17]


A visual hallucination is "the perception of an external visual stimulus where none exists". [18] A separate but related phenomenon is a visual illusion, which is a distortion of a real external stimulus. Visual hallucinations are classified as simple or complex:

For example, one may report hallucinating a giraffe. A simple visual hallucination is an amorphous figure that may have a similar shape or color to a giraffe (looks like a giraffe), while a complex visual hallucination is a discrete, lifelike image that is, unmistakably, a giraffe.


Command hallucinations are hallucinations in the form of commands; they appear to be from an external source, or can appear coming from the subject's head. [19] The contents of the hallucinations can range from the innocuous to commands to cause harm to the self or others. [19] Command hallucinations are often associated with schizophrenia. People experiencing command hallucinations may or may not comply with the hallucinated commands, depending on the circumstances. Compliance is more common for non-violent commands. [20]

Command hallucinations are sometimes used to defend a crime that has been committed, often homicides. [21] In essence, it is a voice that one hears and it tells the listener what to do. Sometimes the commands are quite benign directives such as "Stand up" or "Shut the door." [22] Whether it is a command for something simple or something that is a threat, it is still considered a "command hallucination." Some helpful questions that can assist one in determining if they may have this includes: "What are the voices telling you to do?", "When did your voices first start telling you to do things?", "Do you recognize the person who is telling you to harm yourself (or others)?", "Do you think you can resist doing what the voices are telling you to do?" [22]


Phantosmia (olfactory hallucinations), smelling an odor that is not actually there, [23] and parosmia (olfactory illusions), inhaling a real odor but perceiving it as different scent than remembered, [24] are distortions to the sense of smell (olfactory system), and in most cases, are not caused by anything serious and will usually go away on their own in time. [23] It can result from a range of conditions such as nasal infections, nasal polyps, dental problems, migraines, head injuries, seizures, strokes, or brain tumors. [23] [25] Environmental exposures can sometimes cause it as well, such as smoking, exposure to certain types of chemicals (e.g., insecticides or solvents), or radiation treatment for head or neck cancer. [23] It can also be a symptom of certain mental disorders such as depression, bipolar disorder, intoxication, substance withdrawal, or psychotic disorders (e.g., schizophrenia). [25] The perceived odors are usually unpleasant and commonly described as smelling burned, foul, spoiled, or rotten. [23]


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, formication, is the sensation of insects crawling underneath the skin and is frequently associated with prolonged cocaine use. [26] 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. [26]


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 epilepsy, 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. [27] [28]

General somatic sensations

General somatic sensations of a hallucinatory nature are experienced when an individual feels that their body is being mutilated, i.e. twisted, torn, or disemboweled. 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 this hallucination. [28] [ citation needed ]


A hallucination involving sensory modalities is called multimodal, analogous to unimodal hallucinations which have only one sensory modality. The multiple sensory modalities can occur at the same time (simultaneously) or with a delay (serial), be related or unrelated to each other, and be consistent with reality (congruent) or not (incongruent). [4] [5] For example, a person talking in a hallucination would be congruent with reality, but a cat talking would not be.

Multimodal hallucinations are correlated to poorer mental health outcomes, and are often experienced as feeling more real. [4]


Hallucinations can be caused by a number of factors.

Hypnagogic hallucination

These hallucinations occur just before falling asleep and affect a high proportion of the population: in one survey 37% of the respondents experienced them twice a week. [29] 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 narcolepsy. Hypnagogic hallucinations are sometimes associated with brainstem abnormalities, but this is rare. [30]

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 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. [30]

Delirium tremens

One of the more enigmatic forms of visual hallucination is the highly variable, possibly polymodal delirium tremens. Individuals with 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 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 hallucination may begin with illusions [31] 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 area and pedunculopontine nuclei of the tegmentum. [30]

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. [30]

Charles Bonnet syndrome

Charles Bonnet syndrome is the name given to visual hallucinations experienced by a partially or severely sight impaired person. The hallucinations can occur at any time and can distress people of any age, as they may not initially be aware that they are hallucinating. They may fear for their own mental health initially, which may delay them sharing with carers until they start to understand it themselves. The hallucinations can frighten and disconcert as to what is real and what is not. The hallucinations can sometimes be dispersed by eye movements, or by reasoned logic such as, "I can see fire but there is no smoke and there is no heat from it" or perhaps, "We have an infestation of rats but they have pink ribbons with a bell tied on their necks." Over elapsed months and years, the hallucinations may become more or less frequent with changes in ability to see. The length of time that the sight impaired person can have these hallucinations varies according to the underlying speed of eye deterioration. A differential diagnosis are ophthalmopathic hallucinations. [32]

Focal epilepsy

Visual hallucinations due to focal seizures 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 contralateral 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 toward the ipsilateral side. [27] [33]

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 to be 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 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. [27]

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. [34] Even when consciousness is impaired, insight into the hallucination or illusion is typically preserved.

Drug-induced hallucination

Drug-induced hallucinations are caused by hallucinogens, dissociatives, and deliriants, including many drugs with anticholinergic actions and certain stimulants, which are known to cause visual and auditory hallucinations. Some psychedelics such as lysergic acid diethylamide (LSD) and psilocybin can cause hallucinations that range in the spectrum of mild to intense.

Hallucinations, pseudohallucinations, or intensification of pareidolia, particularly auditory, are known side effects of opioids to different degrees—it may be associated with the absolute degree of agonism or antagonism of especially the kappa opioid receptor, sigma receptors, delta opioid receptor and the NMDA receptors or the overall receptor activation profile as synthetic opioids like those of the pentazocine, levorphanol, fentanyl, pethidine, methadone and some other families are more associated with this side effect than natural opioids like morphine and codeine and semi-synthetics like hydromorphone, amongst which there also appears to be a stronger correlation with the relative analgesic strength. Three opioids, Cyclazocine (a benzormorphan opioid/pentazocine relative) and two levorphanol-related morphinan opioids, Cyclorphan and Dextrorphan are classified as hallucinogens, and Dextromethorphan as a dissociative. [35] [36] [37] These drugs also can induce sleep (relating to hypnagogic hallucinations) and especially the pethidines have atropine-like anticholinergic activity, which was possibly also a limiting factor in the use, the psychotomimetic side effects of potentiating morphine, oxycodone, and other opioids with scopolamine (respectively in the Twilight Sleep technique and the combination drug Skophedal, which was eukodal (oxycodone), scopolamine and ephedrine, called the "wonder drug of the 1930s" after its invention in Germany in 1928, but only rarely specially compounded today) (q.q.v.). [38]

Sensory deprivation hallucination

Hallucinations can be caused by sensory deprivation when it occurs for prolonged periods of time, and almost always occurs in the modality being deprived (visual for blindfolded/darkness, auditory for muffled conditions, etc.) [39]

Experimentally-induced hallucinations

Anomalous experiences, such as so-called benign hallucinations, 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.

The evidence for this statement has been accumulating for more than a century. Studies of benign hallucinatory experiences go back to 1886 and the early work of the Society for Psychical Research, [40] [41] which suggested approximately 10% of the population had experienced at least one hallucinatory episode in the course of their life. More recent studies have validated these findings; the precise incidence found varies with the nature of the episode and the criteria of "hallucination" adopted, but the basic finding is now well-supported. [42]

Non-celiac gluten sensitivity

There is tentative evidence of a relationship with non-celiac gluten sensitivity, the so-called "gluten psychosis". [43]


Dopaminergic and serotonergic hallucinations

It has been reported that in serotonergic hallucinations, the person maintains an awareness that they are hallucinating, unlike dopaminergic hallucinations. [3]


Hallucinations are associated with structural and functional abnormalities in primary and secondary sensory cortices. Reduced grey matter in regions of the superior temporal gyrus/middle temporal gyrus, including Broca's area, is associated with auditory hallucinations as a trait, while acute hallucinations are associated with increased activity in the same regions along with the hippocampus, parahippocampus, and the right hemispheric homologue of Broca's area in the inferior frontal gyrus. [44] Grey and white matter abnormalities in visual regions are associated with visual hallucinations in diseases such as Alzheimer's disease, further supporting the notion of dysfunction in sensory regions underlying hallucinations.

One proposed model of hallucinations posits that over-activity in sensory regions, which is normally attributed to internal sources via feedforward networks to the inferior frontal gyrus, is interpreted as originating externally due to abnormal connectivity or functionality of the feedforward network. [44] This is supported by cognitive studies of those with hallucinations, who have demonstrated abnormal attribution of self generated stimuli. [45]

Disruptions in thalamocortical circuitry may underlie the observed top down and bottom up dysfunction. [46] Thalamocortical circuits, composed of projections between thalamic and cortical neurons and adjacent interneurons, underlie certain electrophysical characteristics (gamma oscillations) that are underlie sensory processing. Cortical inputs to thalamic neurons enable attentional modulation of sensory neurons. Dysfunction in sensory afferents, and abnormal cortical input may result in pre-existing expectations modulating sensory experience, potentially resulting in the generation of hallucinations. Hallucinations are associated with less accurate sensory processing, and more intense stimuli with less interference are necessary for accurate processing and the appearance of gamma oscillations (called "gamma synchrony"). Hallucinations are also associated with the absence of reduction in P50 amplitude in response to the presentation of a second stimuli after an initial stimulus; this is thought to represent failure to gate sensory stimuli, and can be exacerbated by dopamine release agents. [47]

Abnormal assignment of salience to stimuli may be one mechanism of hallucinations. Dysfunctional dopamine signaling may lead to abnormal top down regulation of sensory processing, allowing expectations to distort sensory input. [48]


There are few treatments for many types of hallucinations. However, for those hallucinations caused by mental disease, a psychologist or psychiatrist should be consulted, and treatment will be based on the observations of those doctors. Antipsychotic and atypical antipsychotic medication may also be utilized to treat the illness if the symptoms are severe and cause significant distress.[ citation needed ] 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, stimulant 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. Meta-analyses show that cognitive behavioral therapy [49] and metacognitive training [50] can also reduce the severity of hallucinations.


Prevalence of hallucinations varies depending on underlying medical conditions, [51] [4] which sensory modalities are affected, [5] age [52] [51] and culture. [53] As of 2022, auditory hallucinations are the most well studied and most common sensory modality of hallucinations, with an estimated lifetime prevalence of 9.6%. [52] Children and adolescents have been found to experience similar rates (12.7% and 12.4% respectively) which occur mostly during late childhood and adolescence. This is compared with adults and those over 60 (with rates of 5.8% and 4.8% respectively). [52] [51] For those with schizophrenia, the lifetime prevalence of hallucinations is 80% [4] and the estimated prevalence of visual hallucinations is 27%, compared to 79% for auditory hallucinations. [4] A 2019 study suggested 16.2% of adults with hearing impairment experience hallucinations, with prevalence rising to 24% in the most hearing impaired group. [54]

A risk factor for multimodal hallucinations is prior experience of unimodal hallucinations. [4] In 90% cases of psychosis, a visual hallucination occurs in combination with another sensory modality, most often being auditory or somatic. [4] In schizophrenia, multimodal hallucinations are twice as common as unimodal ones. [4]

A 2015 review of 55 publications from 1962 to 2014 found 16–28.6% of those experiencing hallucinations report at least some religious content in them, [55] :415 along with 20–60% reporting some religious content in delusions. [55] :415 There is some evidence for delusions being a risk factor for religious hallucinations, with and 61.7% of people having experienced any delusion and 75.9% of those having experienced a religious delusion found to also experience hallucinations. [55] :421

See also

Related Research Articles

<span class="mw-page-title-main">Psychosis</span> Abnormal condition of the mind

Psychosis is a condition of the mind that results in difficulties determining what is real and what is not real. Symptoms may include delusions and hallucinations, among other features. Additional symptoms are incoherent speech and behavior that is inappropriate for a given situation. There may also be sleep problems, social withdrawal, lack of motivation, and difficulties carrying out daily activities. Psychosis can have serious adverse outcomes.

<span class="mw-page-title-main">Schizophrenia</span> Mental disorder characterized by psychosis

Schizophrenia is a mental disorder characterized by continuous or relapsing episodes of psychosis. Major symptoms include hallucinations, delusions, and disorganized thinking. Other symptoms include social withdrawal, decreased emotional expression, and apathy. Symptoms typically develop gradually, begin during young adulthood, and in many cases never become resolved. There is no objective diagnostic test; diagnosis is based on observed behavior, a history that includes the person's reported experiences, and reports of others familiar with the person. To be diagnosed with schizophrenia, symptoms and functional impairment need to be present for six months (DSM-5) or one month (ICD-11). Many people with schizophrenia have other mental disorders, especially substance use disorders, depressive disorders, anxiety disorders, and obsessive–compulsive disorder.

Visual release hallucinations, also known as Charles Bonnet syndrome or CBS, are a type of psychophysical visual disturbance in which a person with partial or severe blindness experiences visual hallucinations.

Hypnagogia is the experience of the transitional state from wakefulness to sleep: the hypnagogic state of consciousness, during the onset of sleep. Its opposite state is described as hypnopompic —the transitional state from sleep into wakefulness. Mental phenomena that may occur during this "threshold consciousness" phase include hypnagogic hallucinations, exploding head syndrome, lucid dreaming, and sleep paralysis. The latter two phenomena are themselves separate sleep conditions that are sometimes experienced during the hypnagogic state.

<span class="mw-page-title-main">Mental status examination</span> Way of observing and describing a patients current state of mind

The mental status examination (MSE) is an important part of the clinical assessment process in neurological and psychiatric practice. It is a structured way of observing and describing a patient's psychological functioning at a given point in time, under the domains of appearance, attitude, behavior, mood and affect, speech, thought process, thought content, perception, cognition, insight, and judgment. There are some minor variations in the subdivision of the MSE and the sequence and names of MSE domains.

The Hearing Voices Movement (HVM) is the name used by organizations and individuals advocating the "hearing voices approach", an alternative way of understanding the experience of those people who "hear voices". In the medical professional literature, ‘voices’ are most often referred to as auditory verbal hallucinations. The movement uses the term ‘hearing voices’, which it feels is a more accurate and 'user-friendly' term.

In psychiatry, thought broadcasting is the belief that others can hear or are aware of an individual's thoughts. The person experiencing this symptom can also think that their thoughts are being broadcast through different media, such as the television or the radio. Different people can experience thought broadcasting in different ways. Thought broadcasting is most commonly found among people that have schizophrenia, schizoaffective disorder, or bipolar disorder. People with thought broadcasting rarely admit to having this symptom or to the severity of the symptom. Thought broadcasting is treated with the use of an atypical antipsychotic and in certain cases cognitive behavioral therapy.

This glossary covers terms found in the psychiatric literature; the word origins are primarily Greek, but there are also Latin, French, German, and English terms. Many of these terms refer to expressions dating from the early days of psychiatry in Europe.

Paraphrenia is a mental disorder characterized by an organized system of paranoid delusions with or without hallucinations and without deterioration of intellect or personality.

Multiple complex developmental disorder (MCDD) is a research category, proposed to involve several neurological and psychological symptoms where at least some symptoms are first noticed during early childhood and persist throughout life. It was originally suggested to be a subtype of autistic spectrum disorders (PDD) with co-morbid schizophrenia or another psychotic disorder; however, there is some controversy that not everyone with MCDD meets criteria for both PDD and psychosis. The term multiplex developmental disorder was coined by Donald J. Cohen in 1986.

Anomalous experiences, such as so-called benign hallucinations, 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.

An auditory hallucination, or paracusia, is a form of hallucination that involves perceiving sounds without auditory stimulus. While experiencing an auditory hallucination, the affected person would hear a sound or sounds which did not come from the natural environment.

<span class="mw-page-title-main">Grandiose delusions</span> Subtype of delusion

Grandiose delusions (GD), also known as delusions of grandeur or expansive delusions, are a subtype of delusion that occur in patients with a wide range of psychiatric diseases, including two-thirds of patients in manic state of bipolar disorder, half of those with schizophrenia, patients with the grandiose subtype of delusional disorder, frequently in narcissistic personality disorder, and a substantial portion of those with substance abuse disorders. GDs are characterized by fantastical beliefs that one is famous, omnipotent, wealthy, or otherwise very powerful. The delusions are generally fantastic and typically have a religious, science fictional, or supernatural theme. There is a relative lack of research into GD, in contrast to persecutory delusions and auditory hallucinations. Around 10% of healthy people experience grandiose thoughts at some point in their lives but do not meet full criteria for a diagnosis of GD.

Brief psychotic disorder ⁠— according to the classifications of mental disorders DSM-IV-TR and DSM-5 ⁠— is a psychotic condition involving the sudden onset of at least one psychotic symptom lasting 1 day to 1 month, often accompanied by emotional turmoil. Remission of all symptoms is complete with patients returning to the previous level of functioning. It may follow a period of extreme stress including the loss of a loved one. Most patients with this condition under DSM-5 would be classified as having acute and transient psychotic disorders under ICD-10. Prior to DSM-IV, this condition was called "brief reactive psychosis." This condition may or may not be recurrent, and it should not be caused by another condition.

Musical ear syndrome (MES) describes a condition seen in people who have hearing loss and subsequently develop auditory hallucinations. "MES" has also been associated with musical hallucinations, which is a complex form of auditory hallucinations where an individual may experience music or sounds that are heard without an external source. It is comparable to Charles Bonnet syndrome and some have suggested this phenomenon could be included under this diagnosis.

Childhood schizophrenia is similar in characteristics of schizophrenia that develops at a later age, but has an onset before the age of 13 years, and is more difficult to diagnose. Schizophrenia is characterized by positive symptoms that can include hallucinations, delusions, and disorganized speech; negative symptoms, such as blunted affect and avolition and apathy, and a number of cognitive impairments. Differential diagnosis is problematic since several other neurodevelopmental disorders, including autism spectrum disorder, language disorder, and attention deficit hyperactivity disorder, also have signs and symptoms similar to childhood-onset schizophrenia.

The diagnosis of schizophrenia, a psychotic disorder, is based on criteria in either the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders, or the World Health Organization's International Classification of Diseases (ICD). Clinical assessment of schizophrenia is carried out by a mental health professional based on observed behavior, reported experiences, and reports of others familiar with the person. Diagnosis is usually made by a psychiatrist. Associated symptoms occur along a continuum in the population and must reach a certain severity and level of impairment before a diagnosis is made. Schizophrenia has a prevalence rate of 0.3-0.7% in the United States

A religious delusion is defined as a delusion, or fixed belief not amenable to change in light of conflicting evidence, involving religious themes or subject matter. Religious faith, meanwhile, is defined as a belief in God or a religious doctrine in the absence of evidence. Psychologists, scientists, and philosophers have debated the distinction between the two, which is subjective and cultural.

<span class="mw-page-title-main">Tactile hallucination</span>

Tactile hallucination is the false perception of tactile sensory input that creates a hallucinatory sensation of physical contact with an imaginary object. It is caused by the faulty integration of the tactile sensory neural signals generated in the spinal cord and the thalamus and sent to the primary somatosensory cortex (SI) and secondary somatosensory cortex (SII). Tactile hallucinations are recurrent symptoms of neurological diseases such as schizophrenia, Parkinson's disease, Ekbom's syndrome and delerium tremens. Patients who experience phantom limb pains also experience a type of tactile hallucination. Tactile hallucinations are also caused by drugs such as cocaine and alcohol.

Visual hallucinations in psychosis are hallucinations accompanied by delusions.


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