Hallucination

Hallucinations may be manifested in a variety of forms.{{cite journal | vauthors = Chen E, Berrios GE | title = Recognition of hallucinations: a new multidimensional model and methodology | journal = Psychopathology | volume = 29 | issue = 1 | pages = 54–63 | year = 1996 | pmid = 8711076 | doi = 10.1159/000284972 }} Various forms of hallucinations affect different senses, sometimes occurring simultaneously, creating multiple sensory hallucinations for those experiencing them.

{{main|Auditory hallucination}}

Auditory hallucinations (also known as paracusia){{cite web |title=Paracusia |url=http://medical-dictionary.thefreedictionary.com/paracusia |publisher=thefreedictionary.com |access-date=2008-08-13 |archive-date=2008-05-16 |archive-url=https://web.archive.org/web/20080516090348/http://medical-dictionary.thefreedictionary.com/paracusia |url-status=live }} 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.{{cite book |title=Abnormal Psychology |vauthors=Nolen-Hoeksema S |date=2014 |publisher=McGraw-Hill |edition=6e |page=283}}{{Cite web |title=Auditory Hallucinations: Causes, Symptoms, Types & Treatment |url=https://my.clevelandclinic.org/health/symptoms/23233-auditory-hallucinations |access-date=2024-01-01 |website=Cleveland Clinic |language=en |archive-date=2024-01-01 |archive-url=https://web.archive.org/web/20240101222629/https://my.clevelandclinic.org/health/symptoms/23233-auditory-hallucinations |url-status=live }} Elementary hallucinations are the perception of sounds such as hissing, whistling, an extended tone, and more.{{Cite web |title=Mental State Examination 3 – Perception and Mood – Pathologia |url=https://pathologia.ed.ac.uk/topic/mental-state-examination-3/ |access-date=2024-01-01 |language=en-US |archive-date=2024-01-01 |archive-url=https://web.archive.org/web/20240101222631/https://pathologia.ed.ac.uk/topic/mental-state-examination-3/ |url-status=live }} 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.{{Cite journal |last1=Tracy |first1=Derek |last2=Shergill |first2=Sukhwinder |date=2013-04-26 |title=Mechanisms Underlying Auditory Hallucinations—Understanding Perception without Stimulus |journal=Brain Sciences |language=en |volume=3 |issue=2 |pages=642–669 |doi=10.3390/brainsci3020642 |doi-access=free |pmid=24961419 |pmc=4061847 |issn=2076-3425}}

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.{{Cite journal |last=Chaudhury |first=Suprakash |date=2010 |title=Hallucinations: Clinical aspects and management |journal=Industrial Psychiatry Journal |volume=19 |issue=1 |pages=5–12 |doi=10.4103/0972-6748.77625 |doi-access=free |issn=0972-6748 |pmc=3105559 |pmid=21694785}}

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.{{cite journal |vauthors=Shibayama M |year=2011 |title=[Differential diagnosis between dissociative disorders and schizophrenia] |journal=Seishin Shinkeigaku Zasshi = Psychiatria et Neurologia Japonica |volume=113 |issue=9 |pages=906–911 |pmid=22117396}} However, many people who do not have a diagnosable mental illness may sometimes hear voices as well.{{cite web |date=September 15, 2006 |title=Hearing Voices: Some People Like It |url=http://www.livescience.com/7177-hearing-voices-people.html |url-status=live |archive-url=https://web.archive.org/web/20061102150621/http://www.livescience.com/humanbiology/060915_hearing_voices.html |archive-date=November 2, 2006 |access-date=2006-11-25 |publisher=LiveScience.com |vauthors=Thompson A}} 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.{{Cite journal |last1=Endres |first1=Dominique |last2=Matysik |first2=Miriam |last3=Feige |first3=Bernd |last4=Venhoff |first4=Nils |last5=Schweizer |first5=Tina |last6=Michel |first6=Maike |last7=Meixensberger |first7=Sophie |last8=Runge |first8=Kimon |last9=Maier |first9=Simon J. |last10=Nickel |first10=Kathrin |last11=Bechter |first11=Karl |last12=Urbach |first12=Horst |last13=Domschke |first13=Katharina |last14=Tebartz van Elst |first14=Ludger |date=2020-09-14 |title=Diagnosing Organic Causes of Schizophrenia Spectrum Disorders: Findings from a One-Year Cohort of the Freiburg Diagnostic Protocol in Psychosis (FDPP) |journal=Diagnostics |language=en |volume=10 |issue=9 |pages=691 |doi=10.3390/diagnostics10090691 |doi-access=free |pmid=32937787 |pmc=7555162 |issn=2075-4418}}

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,{{cite journal |last1=Engmann |first1=B. |last2=Reuter |first2=M. |title=Melodiewahrnehmung ohne äußeren Reiz: Halluzination oder Epilepsie? Ein Fallbericht |trans-title=Spontaneous perception of melodies: Hallucination or epilepsy? |language=de |journal=Nervenheilkunde |date=2009 |volume=28 |issue=4 |pages=217–221 |doi=10.1055/s-0038-1628605 }} arteriovenous malformation,{{cite journal |vauthors=Ozsarac M, Aksay E, Kiyan S, Unek O, Gulec FF |date=July 2012 |title=De novo cerebral arteriovenous malformation: Pink Floyd's song "Brick in the Wall" as a warning sign |journal=The Journal of Emergency Medicine |volume=43 |issue=1 |pages=e17–e20 |doi=10.1016/j.jemermed.2009.05.035 |pmid=19682829}} stroke, lesion, abscess, or tumor.{{cite web |date=August 9, 2000 |title=Rare Hallucinations Make Music In The Mind |url=https://www.sciencedaily.com/releases/2000/08/000809065249.htm |url-status=live |archive-url=https://web.archive.org/web/20061205053946/http://www.sciencedaily.com/releases/2000/08/000809065249.htm |archive-date=December 5, 2006 |access-date=2006-12-31 |publisher=ScienceDaily.com}}

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.{{cite journal | vauthors = Schaefer B, Boumans J, van Os J, van Weeghel J | title = Emerging Processes Within Peer-Support Hearing Voices Groups: A Qualitative Study in the Dutch Context | journal = Frontiers in Psychiatry | volume = 12 | pages = 647969 | date = 2021-04-21 | pmid = 33967856 | pmc = 8098806 | doi = 10.3389/fpsyt.2021.647969 | doi-access = free }}

High caffeine consumption has been linked to an increase in likelihood of one experiencing auditory hallucinations.{{Cite web |vauthors=Fiegl A |title=Caffeine Linked to Hallucinations |url=https://www.smithsonianmag.com/arts-culture/caffeine-linked-to-hallucinations-51161154/ |access-date=2024-01-01 |work=Smithsonian Magazine |language=en |archive-date=2024-01-01 |archive-url=https://web.archive.org/web/20240101222629/https://www.smithsonianmag.com/arts-culture/caffeine-linked-to-hallucinations-51161154/ |url-status=live }} 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.{{cite web |date=8 June 2011 |title=Too Much Coffee Can Make You Hear Things That Are Not There |url=http://www.medicalnewstoday.com/articles/227884.php |archive-url=https://web.archive.org/web/20130311185810/http://www.medicalnewstoday.com/articles/227884.php |archive-date=2013-03-11 |work=Medical News Today}}

{{main|Visual hallucination}}

{{see also|Pareidolia|Palinopsia}}

A visual hallucination is "the perception of an external visual stimulus where none exists".{{cite web| vauthors = Pelak V |title=Approach to the patient with visual hallucinations|url=http://www.uptodate.com/contents/approach-to-the-patient-with-visual-hallucinations|website=www.uptodate.com|access-date=2014-08-25|url-status=live|archive-url=https://web.archive.org/web/20140826120056/http://www.uptodate.com/contents/approach-to-the-patient-with-visual-hallucinations|archive-date=2014-08-26}} 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:

• Simple visual hallucinations (SVH) are also referred to as non-formed visual hallucinations and elementary visual hallucinations. These terms refer to lights, colors, geometric shapes, and indiscrete objects. These can be further subdivided into phosphenes which are SVH without structure, and photopsias which are SVH with geometric structures.
• Complex visual hallucinations (CVH) are also referred to as formed visual hallucinations. CVHs are clear, lifelike images or scenes such as people, animals, objects, places, etc.

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.

{{see also|Bicameral mentality}}

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. The contents of the hallucinations can range from the innocuous to commands to cause harm to the self or others.{{cite journal | vauthors = Beck-Sander A, Birchwood M, Chadwick P | title = Acting on command hallucinations: a cognitive approach | journal = The British Journal of Clinical Psychology | volume = 36 | issue = 1 | pages = 139–148 | date = February 1997 | pmid = 9051285 | doi = 10.1111/j.2044-8260.1997.tb01237.x }} 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.{{cite journal | vauthors = Lee TM, Chong SA, Chan YH, Sathyadevan G | title = Command hallucinations among Asian patients with schizophrenia | journal = Canadian Journal of Psychiatry | volume = 49 | issue = 12 | pages = 838–842 | date = December 2004 | pmid = 15679207 | doi = 10.1177/070674370404901207 | doi-access = free }}

Command hallucinations are sometimes used to defend a crime that has been committed, often homicides.{{cite journal |last1=Knoll |first1=James L. |last2=Resnick |first2=Phillip J. |title=Insanity Defense Evaluations: Toward a Model for Evidence-Based Practice |journal=Brief Treatment and Crisis Intervention |date=February 2008 |volume=8 |issue=1 |pages=92–110 |doi=10.1093/brief-treatment/mhm024 }} 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."{{cite web| vauthors = Shea SC |title=Uncovering Command Hallucinations | work = raining Institute for Suicide Assessment |url=http://www.suicideassessment.com/tips/archives.php?action=prod&id=64|url-status=live|archive-url=https://web.archive.org/web/20140102191930/http://www.suicideassessment.com/tips/archives.php?action=prod&id=64|archive-date=2014-01-02}} 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?"

{{main|Phantosmia|Parosmia}}

Phantosmia (olfactory hallucinations), smelling an odor that is not actually there, and parosmia (olfactory illusions), inhaling a real odor but perceiving it as different scent than remembered,{{cite journal | vauthors = Hong SC, Holbrook EH, Leopold DA, Hummel T | title = Distorted olfactory perception: a systematic review | journal = Acta Oto-Laryngologica | volume = 132 | issue = S1 | pages = S27–S31 | date = June 2012 | pmid = 22582778 | doi = 10.3109/00016489.2012.659759 | s2cid = 207416134 }} 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. It can result from a range of conditions such as nasal infections, nasal polyps, dental problems, migraines, head injuries, seizures, strokes, or brain tumors.{{cite journal | vauthors = Leopold D | title = Distortion of olfactory perception: diagnosis and treatment | journal = Chemical Senses | volume = 27 | issue = 7 | pages = 611–615 | date = September 2002 | pmid = 12200340 | doi = 10.1093/chemse/27.7.611 | doi-access = free }} 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. It can also be a symptom of certain mental disorders such as depression, bipolar disorder, intoxication, substance withdrawal, or psychotic disorders (e.g., schizophrenia). The perceived odors are usually unpleasant and commonly described as smelling burned, foul, spoiled, or rotten.{{citation|title=Phantosmia (Smelling Odours That Aren't There)|author=HealthUnlocked|website=NHS Choices|year=2014|url=http://www.nhs.uk/conditions/phantosmia/Pages/Introduction.aspx|access-date=6 August 2016|url-status=live|archive-url=https://web.archive.org/web/20160802124224/http://www.nhs.uk/conditions/phantosmia/Pages/Introduction.aspx|archive-date=2 August 2016}}

{{Main|Tactile hallucination}}

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.{{cite journal | vauthors = Berrios GE | title = Tactile hallucinations: conceptual and historical aspects | journal = Journal of Neurology, Neurosurgery, and Psychiatry | volume = 45 | issue = 4 | pages = 285–293 | date = April 1982 | pmid = 7042917 | pmc = 491362 | doi = 10.1136/jnnp.45.4.285 }} 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.

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.{{cite book |doi=10.1007/978-1-84628-644-5 |title=A Clinical Guide to Epileptic Syndromes and their Treatment |date=2010 |last1=Panayiotopoulos |first1=C. P. |isbn=978-1-84628-643-8 }}{{page needed|date=July 2024}}{{cite book| vauthors = Barker P |title=Assessment in psychiatric and mental health nursing: in search of the whole person|year=1997|publisher=Stanley Thornes Publishers|location=Cheltenham, UK|isbn=978-0-7487-3174-9|page=245}}

Sexual hallucinations are the perception of erogenous or orgasmic stimuli. They may be unimodal or multimodal in nature and frequently involve sensation in the genital region, though it is not exclusive.{{cite journal |last1=Blom |first1=Jan Dirk |last2=Mangoenkarso |first2=Esmeralda |title=Sexual Hallucinations in Schizophrenia Spectrum Disorders and Their Relation With Childhood Trauma |journal=Frontiers in Psychiatry |date=9 May 2018 |volume=9 |page=193 |doi=10.3389/fpsyt.2018.00193 |doi-access=free |pmid=29867612 |pmc=5954108 }} Frequent examples of sexual hallucinations include the sensation of being penetrated, experiencing orgasm, feeling as if one is being touched in an erogenous zone, sensing stimulation in the genitals, feeling the fondling of one's breasts or buttocks and tastes or smells related to sexual activity.{{cite journal |last1=Akhtar |first1=S. |last2=Thomson |first2=J. A. |title=Schizophrenia and sexuality: a review and a report of twelve unusual cases--part I |journal=The Journal of Clinical Psychiatry |date=April 1980 |volume=41 |issue=4 |pages=134–142 |pmid=7364736 }} Visualizations of sexual content and auditory voices making sexually explicit remarks may sometimes be included in this classification. While it features components of other classifications, sexual hallucinations are distinct due to the orgasmic component and unique presentation.{{Cite journal |last=Blom |first=Jan Dirk |date=2024 |title=The Diagnostic Spectrum of Sexual Hallucinations |journal=Harvard Review of Psychiatry|volume=32 |issue=1 |pages=1–14 |doi=10.1097/HRP.0000000000000388 |pmid=38181099 |pmc=11449261 |hdl=1887/3730958 |hdl-access=free }}

The regions of the brain responsible differ by the subsection of sexual hallucination. In orgasmic auras, the mesial temporal lobe, right amygdala and hippocampus are involved.Penfield W, Rasmussen T. The cerebral cortex of man: a clinical study of localization of function. London: Macmillan, 1950.{{page needed|date=July 2024}}{{cite journal |last1=Janszky |first1=J |last2=Ebner |first2=A |last3=Szupera |first3=Z |last4=Schulz |first4=R |last5=Hollo |first5=A |last6=Szücs |first6=A |last7=Clemens |first7=B |title=Orgasmic aura—a report of seven cases |journal=Seizure |date=September 2004 |volume=13 |issue=6 |pages=441–444 |doi=10.1016/j.seizure.2003.09.005 |pmid=15276150 }} In males, genital specific sensations are related to the postcentral gyrus and arousal and ejaculation are linked to stimulation in the posterior frontal lobe.Sem-Jacobsen CW. Depth-electrographic stimulation of the human brain and behavior. Toronto: Ryerson, 1968.{{page needed|date=July 2024}}{{cite journal |last1=Surbeck |first1=Werner |last2=Bouthillier |first2=Alain |last3=Nguyen |first3=Dang Khoa |title=Bilateral cortical representation of orgasmic ecstasy localized by depth electrodes |journal=Epilepsy & Behavior Case Reports |date=2013 |volume=1 |pages=62–65 |doi=10.1016/j.ebcr.2013.03.002 |pmid=25667829 |pmc=4150648 }} In females, however, the hippocampus and amygdala are connected.{{cite journal |last1=Chaton |first1=Laurence |last2=Chochoi |first2=Maxime |last3=Reyns |first3=Nicolas |last4=Lopes |first4=Renaud |last5=Derambure |first5=Philippe |last6=Szurhaj |first6=William |title=Localization of an epileptic orgasmic feeling to the right amygdala, using intracranial electrodes |journal=Cortex |date=December 2018 |volume=109 |pages=347–351 |doi=10.1016/j.cortex.2018.07.013 |pmid=30126613 }} Limited studies have been done to understand the mechanism of action behind sexual hallucinations in epilepsy, substance use, and post-traumatic stress disorder etiologies.

Somatic hallucinations refer to an interoceptive sensory experience in the absence of stimulus. Somatic hallucinations can be broken down into further subcategories: general, algesic, kinesthetic, and cenesthopathic.

• Cenesthopathic- Effecting the cenesthetic sensory modality, cenesthopathic hallucinations are a pathological alteration in the sense of bodily existence, caused by aberrant bodily sensations. Most often, cenesthopathic hallucinations will refer to sensation in the visceral organs. Therefore, it is also known as visceral hallucinations.{{cite journal |last1=Lim |first1=Anastasia |last2=Hoek |first2=Hans W. |last3=Deen |first3=Mathijs L. |last4=Blom |first4=Jan Dirk |last5=Bruggeman |first5=Richard |last6=Cahn |first6=Wiepke |last7=de Haan |first7=Lieuwe |last8=Kahn |first8=René S. |last9=Meijer |first9=Carin J. |last10=Myin-Germeys |first10=Inez |last11=van Os |first11=Jim |last12=Wiersma |first12=Durk |title=Prevalence and classification of hallucinations in multiple sensory modalities in schizophrenia spectrum disorders |journal=Schizophrenia Research |date=October 2016 |volume=176 |issue=2–3 |pages=493–499 |doi=10.1016/j.schres.2016.06.010 |pmid=27349814 }} Manifestations are often subjective, hard to describe and unique to the sufferer. Common manifestations include pressure, burning, tickling, or tightening in various body systems.{{cite journal |last1=Bilder |first1=R. M. |title=The Neuroscience of Hallucinations |journal=Archives of Clinical Neuropsychology |date=August 2013 |volume=28 |issue=5 |pages=511–512 |doi=10.1093/arclin/act029 }} While these hallucinations can be experienced by a variety of psychiatric and neurological disorder, cenesthopathic schizophrenia is recognized by the ICD as a subtype of schizophrenia marked by primarily cenesthopathic hallucinations and other body image aberrations.{{cite journal |last1=Jenkins |first1=Gary |last2=Röhricht |first2=Frank |title=From Cenesthesias to Cenesthopathic Schizophrenia: A Historical and Phenomenological Review |journal=Psychopathology |date=2007 |volume=40 |issue=5 |pages=361–368 |doi=10.1159/000106314 |pmid=17657136 }}
• Kinesthetic- Kinesthetic hallucinations, effecting the sensory modality of the same name, are the sensation of movement of the limbs or other body parts without actual movement.{{cite journal |last1=Moreno |first1=F. Cartas |last2=Barea |first2=M. ValverDe |title=A first psychotic episode with kinesthetic hallucinations. Report of a case |journal=European Psychiatry |date=April 2021 |volume=64 |issue=S1 |pages=S795 |doi=10.1192/j.eurpsy.2021.2101 |pmc=9479843 }}
• Algesic- Algesic hallucinations, effecting the algesic sensory modality, refers to a perceived perception of pain.
• General- General somatic hallucination refers to somatic hallucinations not otherwise categorized by the above subsections. Common examples include 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.

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). 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.

{{See also|Psychosis#Causes|l1=Psychosis (causes)}}

Hallucinations can be caused by a number of factors.{{Cite web |vauthors=Patterson C, Procter N |date=2023-05-24 |title=Hallucinations in the movies tend to be about chaos, violence and mental distress. But they can be positive too |url=http://theconversation.com/hallucinations-in-the-movies-tend-to-be-about-chaos-violence-and-mental-distress-but-they-can-be-positive-too-204547 |access-date=2023-05-28 |website=The Conversation |language=en |archive-date=2023-05-28 |archive-url=https://web.archive.org/web/20230528043352/http://theconversation.com/hallucinations-in-the-movies-tend-to-be-about-chaos-violence-and-mental-distress-but-they-can-be-positive-too-204547 |url-status=live }}

{{Main|Hypnagogia}}

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.{{cite journal | vauthors = Ohayon MM, Priest RG, Caulet M, Guilleminault C | title = Hypnagogic and hypnopompic hallucinations: pathological phenomena? | journal = The British Journal of Psychiatry | volume = 169 | issue = 4 | pages = 459–467 | date = October 1996 | pmid = 8894197 | doi = 10.1192/bjp.169.4.459 | s2cid = 3086394 }} 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.{{cite journal | vauthors = Manford M, Andermann F | title = Complex visual hallucinations. Clinical and neurobiological insights | journal = Brain | volume = 121 ( Pt 10) | issue = 10 | pages = 1819–1840 | date = October 1998 | pmid = 9798740 | doi = 10.1093/brain/121.10.1819 | doi-access = free }}

{{main|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.

{{main|Delirium tremens}}

One of the more enigmatic forms of visual hallucination is the highly variable, possibly polymodal delirium tremens. It is associated with withdrawal in alcohol use disorder. Individuals with delirium tremens may be agitated and confused, especially in the later stages of this disease.{{cite book |vauthors=Rahman A, Paul M |chapter=Delirium Tremens |date=2023 |chapter-url=http://www.ncbi.nlm.nih.gov/books/NBK482134/ |title=StatPearls |access-date=2024-01-08 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=29489272 |archive-date=2023-12-04 |archive-url=https://web.archive.org/web/20231204231124/https://www.ncbi.nlm.nih.gov/books/NBK482134/ |url-status=live }} 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.{{cite journal | vauthors = Grover S, Ghosh A | title = Delirium Tremens: Assessment and Management | journal = Journal of Clinical and Experimental Hepatology | volume = 8 | issue = 4 | pages = 460–470 | date = December 2018 | pmid = 30564004 | pmc = 6286444 | doi = 10.1016/j.jceh.2018.04.012 }}

Parkinson's disease is linked with Lewy body dementia for their similar hallucinatory symptoms. Presence hallucinations can be an early indicator of cognitive decline in Parkinson's Disease.{{Cite web |last=Franchina |first=Phil |date=2023-06-30 |title=Presence Hallucinations as an Early Indicator of Cognitive Decline in Parkinson's Disease |url=https://www.apdaparkinson.org/article/presence-hallucinations-as-an-early-indicator-of-parkinsons-disease/ |access-date=2024-07-27 |website=American Parkinson Disease Association |language=en-US}} 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{{cite web | url = https://www.nytimes.com/2006/02/14/health/14case.html | vauthors = Derr D | archive-url = https://web.archive.org/web/20110926153757/http://www.nytimes.com/2006/02/14/health/14case.html | archive-date=2011-09-26 | title = Marilyn and Me | work = The New York Times | date = 14 February 2006 }} 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.

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.

{{see also|Migraine aura|Scintillating scotoma}}

Migraine attacks may result in visual hallucinations including auras and in rarer cases, auditory hallucinations.{{Cite web |last=Zegar |first=Amir |date=2022-12-15 |title=Migraine Doctor Rice Village 77005 |url=https://riceemergencyroom.com/can-migraines-cause-hallucinations/ |access-date=2024-07-27 |website=Rice Emergency Room |language=en-US}}

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.{{cite journal | vauthors = Engmann B |title=Phosphene und Photopsien – Okzipitallappeninfarkt oder Reizdeprivation? |trans-title=Phosphenes and photopsias - ischaemic origin or sensorial deprivation? - Case history |journal=Zeitschrift für Neuropsychologie |volume=19 |issue=1 |pages=7–13 |year=2008 |doi=10.1024/1016-264X.19.1.7 |language=de }}

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.{{cite journal | vauthors = Teeple RC, Caplan JP, Stern TA | title = Visual hallucinations: differential diagnosis and treatment | journal = Primary Care Companion to the Journal of Clinical Psychiatry | volume = 11 | issue = 1 | pages = 26–32 | year = 2009 | pmid = 19333408 | pmc = 2660156 | doi = 10.4088/PCC.08r00673 }}

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.

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.{{cite journal | vauthors = Bien CG, Benninger FO, Urbach H, Schramm J, Kurthen M, Elger CE | title = Localizing value of epileptic visual auras | journal = Brain | volume = 123 ( Pt 2) | issue = 2 | pages = 244–253 | date = February 2000 | pmid = 10648433 | doi = 10.1093/brain/123.2.244 | doi-access = free }} Even when consciousness is impaired, insight into the hallucination or illusion is typically preserved.{{Cite journal |last1=Teeple |first1=Ryan C. |last2=Caplan |first2=Jason P. |last3=Stern |first3=Theodore A. |date=2009-02-15 |title=Visual Hallucinations: Differential Diagnosis and Treatment |url=https://www.psychiatrist.com/pcc/visual-hallucinations-differential-diagnosis-treatment |journal=The Primary Care Companion to the Journal of Clinical Psychiatry |volume=11 |issue=1 |pages=26–32 |doi=10.4088/PCC.08r00673 |pmid=19333408 |pmc=2660156 |issn=1523-5998}}

{{main|Hallucinogen}}

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.{{citation needed|date=January 2024}}

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.{{cite web|url=https://www.mayoclinic.org/drugs-supplements/fentanyl-transdermal-route/side-effects/drg-20068152|title=Fentanyl (Transdermal Route) Side Effects - Mayo Clinic|website=Mayo Clinic|archive-url=https://web.archive.org/web/20180424203224/https://www.mayoclinic.org/drugs-supplements/fentanyl-transdermal-route/side-effects/drg-20068152|archive-date=2018-04-24|url-status=live|access-date=2018-04-24}}{{cite web |url=https://www.drugs.com/pro/talwin-injection.html |title=Talwin Injection - FDA prescribing information, side effects and uses |access-date=2018-04-24 |url-status=live |archive-url=https://web.archive.org/web/20180424202933/https://www.drugs.com/pro/talwin-injection.html |archive-date=2018-04-24 }}{{cite web|url=https://healthyliving.azcentral.com/prescription-drugs-that-can-cause-hallucinations-12212355.html|title=Prescription Drugs That Can Cause Hallucinations|website=azcentral.com|access-date=2018-04-24|archive-date=2021-08-28|archive-url=https://web.archive.org/web/20210828095840/https://healthyliving.azcentral.com/marijuanas-effect-on-depakote-for-manic-depression-12248490.html|url-status=live}} 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.).{{cite journal | vauthors = Trauner R, Obwegeser H | title = The surgical correction of mandibular prognathism and retrognathia with consideration of genioplasty. I. Surgical procedures to correct mandibular prognathism and reshaping of the chin | journal = Oral Surgery, Oral Medicine, and Oral Pathology | volume = 10 | issue = 7 | pages = 677–89; contd | date = July 1957 | pmid = 13441284 | doi = 10.1016/S0030-4220(57)80063-2 }}

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.){{cite journal | vauthors = Mason OJ, Brady F | title = The psychotomimetic effects of short-term sensory deprivation | language = en-US | journal = The Journal of Nervous and Mental Disease | volume = 197 | issue = 10 | pages = 783–785 | date = October 2009 | pmid = 19829208 | doi = 10.1097/NMD.0b013e3181b9760b | s2cid = 23079468 }}

{{Main|Hallucinations in the sane}}

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,{{cite book | vauthors = Gurney E, Myers FW, Podmore F | date = 1886 | title = Phantasms of the Living, Vols. I and II | location = London | publisher = Trubner and Co. }}{{cite journal | vauthors = Sidgwick E, Johnson A, etal | date = 1894 | title = Report on the Census of Hallucinations | location = London | journal = Proceedings of the Society for Psychical Research | volume = X }} 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.{{cite book | vauthors = Slade PD, Bentall RP | date = 1988 | title = Sensory Deception: a scientific analysis of hallucination | location = London | publisher = Croom Helm }}

There is tentative evidence of a relationship with non-celiac gluten sensitivity, the so-called "gluten psychosis".{{cite journal | vauthors = Losurdo G, Principi M, Iannone A, Amoruso A, Ierardi E, Di Leo A, Barone M | title = Extra-intestinal manifestations of non-celiac gluten sensitivity: An expanding paradigm | journal = World Journal of Gastroenterology | volume = 24 | issue = 14 | pages = 1521–1530 | date = April 2018 | pmid = 29662290 | pmc = 5897856 | doi = 10.3748/wjg.v24.i14.1521 | type = Review | doi-access = free }}

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

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.{{cite book |doi=10.1007/7854_2010_54 |chapter=Functional Brain Imaging in Schizophrenia: Selected Results and Methods |title=Behavioral Neurobiology of Schizophrenia and Its Treatment |series=Current Topics in Behavioral Neurosciences |date=2010 |volume=4 |pages=181–214 |pmid=21312401 |isbn=978-3-642-13716-7 | vauthors = Brown GG, Thompson WK }} Grey and white matter abnormalities in visual regions are associated with hallucinations in diseases such as Alzheimer's disease, further supporting the notion of dysfunction in sensory regions underlying hallucinations.{{cite journal | vauthors = El Haj M, Roche J, Jardri R, Kapogiannis D, Gallouj K, Antoine P | title = Clinical and neurocognitive aspects of hallucinations in Alzheimer's disease | journal = Neuroscience and Biobehavioral Reviews | volume = 83 | pages = 713–720 | date = December 2017 | pmid = 28235545 | pmc = 5565710 | doi = 10.1016/j.neubiorev.2017.02.021 }}

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. This is supported by cognitive studies of those with hallucinations, who have demonstrated abnormal attribution of self generated stimuli.{{cite journal | vauthors = Boksa P | title = On the neurobiology of hallucinations | journal = Journal of Psychiatry & Neuroscience | volume = 34 | issue = 4 | pages = 260–262 | date = July 2009 | pmid = 19568476 | pmc = 2702442 }}

Disruptions in thalamocortical circuitry may underlie the observed top down and bottom up dysfunction.{{cite journal | vauthors = Kumar S, Soren S, Chaudhury S | title = Hallucinations: Etiology and clinical implications | journal = Industrial Psychiatry Journal | volume = 18 | issue = 2 | pages = 119–126 | date = July 2009 | pmid = 21180490 | pmc = 2996210 | doi = 10.4103/0972-6748.62273 | doi-access = free }} Thalamocortical circuits, composed of projections between thalamic and cortical neurons and adjacent interneurons, underlie certain electrophysical characteristics (gamma oscillations) that are associated with 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.{{cite journal | vauthors = Behrendt RP | title = Dysregulation of thalamic sensory "transmission" in schizophrenia: neurochemical vulnerability to hallucinations | journal = Journal of Psychopharmacology | volume = 20 | issue = 3 | pages = 356–372 | date = May 2006 | pmid = 16174672 | doi = 10.1177/0269881105057696 | s2cid = 17104995 }}

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.{{cite book| vauthors = Aleman A, Vercammon A | veditors = Jardri R, Cachia A, Pins D, Thomas P |title=The Neuroscience of Hallucinations|publisher=Springer|chapter=The Bottom Up and Top Down Components of Hallucinatory Phenomenon}}

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.{{Cite web |title=Hallucinations: Definition, Causes, Treatment & Types |url=https://my.clevelandclinic.org/health/symptoms/23350-hallucinations |access-date=2024-01-08 |website=Cleveland Clinic |language=en |archive-date=2024-01-08 |archive-url=https://web.archive.org/web/20240108210225/https://my.clevelandclinic.org/health/symptoms/23350-hallucinations |url-status=live }} 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{{cite journal | vauthors = Turner DT, Burger S, Smit F, Valmaggia LR, van der Gaag M | title = What Constitutes Sufficient Evidence for Case Formulation-Driven CBT for Psychosis? Cumulative Meta-analysis of the Effect on Hallucinations and Delusions | journal = Schizophrenia Bulletin | volume = 46 | issue = 5 | pages = 1072–1085 | date = March 2020 | pmid = 32221536 | pmc = 7505201 | doi = 10.1093/schbul/sbaa045 }} and metacognitive training{{cite journal | vauthors = Penney D, Sauvé G, Mendelson D, Thibaudeau É, Moritz S, Lepage M | title = Immediate and Sustained Outcomes and Moderators Associated With Metacognitive Training for Psychosis: A Systematic Review and Meta-analysis | journal = JAMA Psychiatry | date = March 2022 | volume = 79 | issue = 5 | pages = 417–429 | pmid = 35320347 | pmc = 8943641 | doi = 10.1001/jamapsychiatry.2022.0277 }} can also reduce the severity of hallucinations. Furthermore, there are recovery movements all around the world that advocate for individuals with schizophrenia or voice-hearers (individuals that hear voices). The Hearing Voices Movement,{{cite web | vauthors = ((Wikipedia contributors)) | title = Hearing Voices Movement | date = February 2024 | url = https://en.wikipedia.org/wiki/Hearing_Voices_Movement | access-date = 2024-03-03 | archive-date = 2023-11-28 | archive-url = https://web.archive.org/web/20231128085921/https://en.wikipedia.org/wiki/Hearing_Voices_Movement | url-status = live }}{{Circular reference|date=May 2024}} starting in Europe, aims to{{POV statement|date=October 2024}} utilize knowledge and experience of voice hearers combined with experts in disorders such as schizophrenia, such as psychiatrists.

Prevalence of hallucinations varies depending on underlying medical conditions,{{cite journal | vauthors = de Leede-Smith S, Barkus E | title = A comprehensive review of auditory verbal hallucinations: lifetime prevalence, correlates and mechanisms in healthy and clinical individuals | journal = Frontiers in Human Neuroscience | volume = 7 | pages = 367 | date = 2013 | pmid = 23882203 | pmc = 3712258 | doi = 10.3389/fnhum.2013.00367 | doi-access = free }} which sensory modalities are affected, age{{cite journal | vauthors = Maijer K, Begemann MJ, Palmen SJ, Leucht S, Sommer IE | title = Auditory hallucinations across the lifespan: a systematic review and meta-analysis | journal = Psychological Medicine | volume = 48 | issue = 6 | pages = 879–888 | date = April 2018 | pmid = 28956518 | doi = 10.1017/s0033291717002367 | s2cid = 3820537 }} and culture.{{Cite book |vauthors=Bunevičius P, Stompe R, Adomaitienė T, Vaškelytė V, Kupčinskas JJ, Stakišaitis L, Meilius D, Liubarskienė K, Bhui ZV, Kaunas K |url=http://worldcat.org/oclc/654554799 |title=The impact of personal religiosity and culture on the content of delusions and hallucinations in schizophrenia |date=2008-09-08 |publisher=Lithuanian Academic Libraries Network (LABT) |oclc=654554799 |access-date=2022-04-26 |archive-date=2024-03-04 |archive-url=https://web.archive.org/web/20240304002336/https://search.worldcat.org/title/654554799 |url-status=live }} {{As of|2022|post=,}} auditory hallucinations are the most well studied and most common sensory modality of hallucinations, with an estimated lifetime prevalence of 9.6%. 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). For those with schizophrenia, the lifetime prevalence of hallucinations is 80% and the estimated prevalence of visual hallucinations is 27%, compared to 79% for auditory hallucinations. A 2019 study suggested 16.2% of adults with hearing impairment experience hallucinations, with prevalence rising to 24% in the most hearing impaired group.{{cite journal |last1=Linszen |first1=M. M. J. |last2=van Zanten |first2=G. A. |last3=Teunisse |first3=R. J. |last4=Brouwer |first4=R. M. |last5=Scheltens |first5=P. |last6=Sommer |first6=I. E. |title=Auditory hallucinations in adults with hearing impairment: a large prevalence study |journal=Psychological Medicine |date=January 2019 |volume=49 |issue=1 |pages=132–139 |doi=10.1017/S0033291718000594 |pmid=29554989 |url=https://pure.rug.nl/ws/files/78351692/Auditory_hallucinations_in_adults_with_hearing_impairment.pdf }}

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

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,{{cite journal | vauthors = Cook CC | title = Religious psychopathology: The prevalence of religious content of delusions and hallucinations in mental disorder | journal = The International Journal of Social Psychiatry | volume = 61 | issue = 4 | pages = 404–425 | date = June 2015 | pmid = 25770205 | pmc = 4440877 | doi = 10.1177/0020764015573089 }}{{Rp|page=415}} along with 20–60% reporting some religious content in delusions.{{Rp|page=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.{{Rp|page=421}}

{{col div|colwidth=20em}}

• Anomalous experiences

• Apparitional experience

• Bicameral mentality

• Closed-eye hallucination
• Delusion
• Dimethyltryptamine
• Folie à deux
• Ganzfeld effect

• Hallucination (artificial intelligence)

• Hallucinogen persisting perception disorder HPPD

• Hallucinogenic fish
• Illusion
• Hypnagogia
• Microwave auditory effect
• Phantom eye syndrome

• Phantom limb

• Phantosmia

• Phosphene
• Prisoner's cinema

• Pseudohallucination

• Psychedelic experience
• Psychotic depression

• Schizophrenia

• Simulated reality
• Vision (spirituality)
• Visual release hallucinations

{{colend}}

{{Reflist}}

{{refbegin}}

• {{cite book | vauthors = Johnson FH |title=The Anatomy of Hallucinations |date=1978 |publisher=Nelson-Hall |location=Chicago |isbn=0-88229-155-6}}
• {{cite book | vauthors = Slade PD, Bentall RP |title=Sensory Deception: A Scientific Analysis of Hallucination |date=1988 |publisher=Croom Helm |location=London Sydney |isbn=0-7099-3961-2}}
• {{cite book | vauthors = Aleman A, Larøi F |title=Hallucinations: The Science of Idiosyncratic Perception |date=2008 |publisher=American Psychological Association |location=Washington, DC |isbn=978-1-4338-0311-6}}
• {{cite book | vauthors = Sacks OW |title=Hallucinations |date=2012 |publisher=Knopf |location=New York |isbn=978-0-307-95724-5 |edition=1. American}}

{{refend}}

{{Medical resources

| DiseasesDB = 19769

| ICD10 = {{ICD10|R|44||r|40}}

| ICD9 = {{ICD9|780.1}}

| ICDO =

| OMIM =

| MedlinePlus = 003258

| eMedicineSubj =

| eMedicineTopic =

| MeshID = D006212

}}

{{Commons category}}

{{wikiquote}}

• [https://www.hearing-voices.org/ Hearing Voices Network]
• {{cite web |url=http://www.psychanalyse-paris.com/843-Anthropology-and.html |title=Anthropology and Hallucinations; chapter from The Making of Religion |author= |date=November 4, 2006 |website=psychanalyse-paris.com |access-date=October 4, 2016 |archive-date=May 29, 2016 |archive-url=https://web.archive.org/web/20160529110305/http://psychanalyse-paris.com/843-Anthropology-and.html |url-status=dead }}
• [https://sites.dartmouth.edu/dujs/2009/11/21/hallucination-a-normal-phenomenon/ Hallucination: A Normal Phenomenon?]
• [http://www.math.utah.edu/~bresslof/publications/01-1.pdf Geometric visual hallucinations, Euclidean symmetry and the functional architecture of striate cortex]

{{Cognition, perception, emotional state and behaviour symptoms and signs}}

{{Authority control}}

Category:Medical signs

Category:Nonexistent things

Category:Symptoms and signs of mental disorders