Click on these buttons to visit our journals
Return to Psychiatry On-Line Return to Dentistry On-Line Return to Vet On-Line Return to GP On-Line Link to Pharmacy on-Line Return to Anaesthesia On-Line Return to Medicine On-Line Return to Family Medical Practice On-Line


Hallucinations and illusions
of non-psychiatric aetiologies

Ramon A Boza, M.D.
Clinical Associate Professor, University of Miami
Consultant Psychiatrist, Miami Veterans Hospital



I) Hallucinations during psychological events
II) Use of Psychotomimetics and prescribed medication
III) Neurological and Sleep disorders
IV) Medico-Surgical conditions
V) Environmental and Industrial causes
VI) Pseudohallucinations


Hallucinations are defined as "an apparent perception of an external object when no such object is present" (1). It is to be differentiated from illusions in which real perceptions are misinterpreted. Although typically associated with psychiatric disorders, the hallucinatory experience has a wide range of etiologies that may include but is not limited to the following: neurological insult, seizure and sleep disorders, drug reactions, substance abuse, grief, stress, as well as metabolic, endocrine and infectious diseases.

Within this broad range of possible causes, we will attempt a comprehensive classification and description of the phenomena of hallucination and illusion. The following sections relate to all- inclusive, significant non-psychiatric etiologies:

I) Hallucinations during psychological events

The term hallucination (from the Latin alucinari "to wander in mind") was introduced to the psychiatric literature by Esquirol in 1837. Hallucinations have been regarded as a restitutive symptom in Schizophrenia, as an attempt to make sense of a severe thought disorder. The American Psychiatric Association, Diagnostic Statistic Manual (2) criterion for the diagnosis of Schizophrenia requires "prominent hallucinations throughout the day, voices [unrelated] to depression or elation, a running commentary on the person, and two or more voices conversing with each other". It is also found as a symptom frequently associated to the severity of other mental illnesses.

However, in this review we will not refer to psychiaric conditions “per se”, but to specific psychological circumstances, in which the illusory-hallucinatory phenomena may be present.

a) In states of Mourning and Stress, voices can provide a sense of calmness and assurance. Geronimo, (3) the Apache leader, while grieving the massacre of his family, heard the message "no gun will ever kill you". From that day on, he believed he could not die by a bullet, and his daring in battle may have been partially based, on that assumption.

b) Sensory Deprivation can account for hallucinatory phenomena. Solomon et al. (4) quote from numerous autobiographies of explorers describing these events, i.e. Slocum, in his solo trip around the world, was directed during a gale to the right course by a hallucinated pilot. Brainwashing as experienced by POWs, jailed dissidents in totalitarian states, or terrorists' hostages, may also experience auditory perceptual disturbances.

c) Sleep Deprivation, as seen in critical situations, use of psychostimulants, or political torture; may evoke dream imagery with comforting visual hallucinations erupting into the waking state. REM (Rapid-Eye Movement) fragments of the paradoxical stage of sleep may also appear in mixed states of sleep deprivation, fatigue, and boredom as when driving for long periods of time ("highway hypnosis").

d) Acquired Deafness. Musical hallucinations have been reported in patients suffering from acquired deafness. Sacks (5) wrote of David Wright, the South African poet, deaf since age seven. He heard "phantasmal voices" only when someone spoke to him, and could see his face and gestures. It is conceivable that, the skilled, post-lingual deaf, automatically translate the lip- reading into an auditory hallucinated equivalent.

e) Phantom limbs has been defined as proprioceptive hallucination of a limb, or other part of the body, that has been excised. Though the patient is fully aware of the amputation, he still feels that part of the body appended, moving, pained, or with other unusual paresthetic sensations (6).

f) Flashbacks (Post Hallucinogenic Perceptual Disorders), were originally described by Cohen (7) as secondary to the widespread use of hallucinogens. They seldom appear after more than a year without drugs. He reported visual slowing in the perception of time. Flashbacks, visual as well as olfactory, have also been reported as associated with Post Traumatic Stress Disorders (PTSD). A veteran reported that certain smells, such as gasoline or smoke, could trigger vivid flashbacks of combat memories. During a recent natural disaster (Hurricane Andrew), some of our patients reported that the heat, cold food, and the sound of the "choppers" threw them into vivid visual and olfactory hallucinations, from their Vietnam experiences of twenty years earlier.

II) Use of Psychotomimetics and prescribed medications

a) Psychedelic drugs: In 1938, Hoffman (8) synthesized a new compound he thought could have analeptic properties. Eventually, he carried out a self-experiment in which he ingested lysergic acid diethylamide (LSD) and reported: "[It] surged upon me an uninterrupted stream of fantastic [kaleidoscopic-like]images of extraordinary plasticity and vividness". He also noticed, the phenomena of synesthesias (receiving stimuli through a different sensory channel, such as seeing voices, or hearing colors), and trailing (moving objects are seen as a series of discrete and discontinuous images similar to stroboscopic photography or discotheque light effects).

Phencyclidine (PCP), as well as peyote, mescal, psilocybin, and, rarely, cannabis, tetrahydrocannabinol (THC), and the "phenylethylamine designer drugs", (3-4-methylene-dioxy- methamphetamine, (Ecstasy); 3-5 methylene-dioxy-etamphetamine (Eve), ("Ice"), methamphetamine consumed through smoking; can generate bizarre, colorful visions with peculiar forms such as lattice, grating, or spirals. Artists and aesthetes of the “fin de siecle” such as Poe, Coleridge, de Quincey, Baudelaire and Gauthier, used hashish and opiates as means to increase their visual imagery and artistic creativity.

b) Prescriptions and Over the Counter Medications (OTC)

1) Visual hallucinations:

Some of the pharmacological agents that might generate hallucinations are the following: Alpha-adrenergic agonist anti- hypertensives like clonidine; the anti-parkinsonian agents such as bromocriptine, selegiline, and carbidopa; the anti-convulsant carbamazepine; analgesics like pentazocine and fentanyl; and anti-vertigo drugs like diphenidol. Also the psychotropic agents with robust anti-cholinergic effects, as well as the serotonin re-uptake blocker antidepressants (SSRI). The histamine-2 blocker used in the treatment of peptic ulcer disease are also capable of generating hallucinations. Antiarrhythmic agents, such as tonocaide, may be hallucinogenic in close to 12 % of patients.

Finally, dronabinol, an antiemetic cannabinoid used in the treatment of nausea associated with chemotherapy, can generate hallucinations in up to 5 % of cases (9).

a) Chromatopsias are illusions in which the environment is seen as uniformly tinted with a color. Xanthopsias (yellow vision) have been reported with Digitalis use (10), and purple vision may be seen with Santonin, an anti-helminthic (11).

b) Size hallucinations: Lilliputians are real hallucinations in which the patients see imaginary people of a small size, usually associated with pleasant feelings. Brodnignagian hallucinations, are just the opposite, people may be seen as giants.

c) Metamorphosias, are visual illusions (12). They may include the following: Dysmegalopsia, (alterations in the form of objects), micropsia and macropsia in which real visual perceptions are seen smaller or larger than they really are. Micropsia can be accompanied by teleopsia, in which the minified object is seen far away. In pelopsia objects are seen as getting closer. Allesthesia modifies the perception of the place where a true object really is. Palinopsia, is a persistent visual sensation after the object has been removed from the patient's visual field. These events have more an illusory than hallucinatory quality, and are frequently associated with either parietal lobe pathology or as a component of a migrainous aura.

2).- Tactile (haptic), proprioceptive, somatic, and visceral hallucinations.

Drug related: Formicative hallucinations are tactile phenomena found with the abuse of Alcohol, Methylphenidate, Amphetamines, and Steroids. The patients complain of "bugs" crawling in their skin, and may vigorously scratch themselves. Some of the most severe, chronic cases have been successfully treated with the neuroleptic pimozide (13). Use of Amyl nitrate (14) as an inhalant may arouse erotic sensations in the genital area. It has also been used to evoke a sense of prolonged orgasmic pleasure.

III) Hallucinations of neurological aetiology:

a) Epilepsy. Abnormal electric activity in diverse brain localizations may elicit hallucinatory phenomena of a peculiar nature. Alajouanine (15) quotes from Dostoyevsky's experience of an auditory aura and a sense of Epiphany: "The air was filled with a big noise and I thought it had engulfed me. I have really touched God. [No one] can imagine the happiness [epileptics] feel the second before our fit. Mahomet, in the Koran, said he has seen the Paradise... I don't know if this felicity lasts for seconds, hours or months, but, for all the joys life brings, I would not exchange this one".

Penrose and Wilder (16) reported many kinds of sensory seizures, such as feelings of numbness, tingling, heat, or water running in patients with centro-parietal foci. Abnormal electric hallucinations. Occipital cortical discharges can generate elementary visual hallucinations such as light spots, twirling objects, and geometrical figures. Etiology may include, traumatic cortical scars, post-concussion syndrome, neoplasms, infarctions, vascular malformations, lupus erythematous, degenerative, vasculitic lesions, or metabolic insult.

Olfactory, or uncinate seizures, are mostly reported as unpleasant odors, such as burning rubber, feces, rotting manure, sulfur, or indescribable. Frequently, the olfactory hallucinations are associated with aural gustatory hallucinations. The patient may describe elementary tastes like sweet, salty, bitter, or odd flavors.

Gustatory hallucinations are seldom found as an early sign of cognitive derrangement. One of our veterans, began to complain of having a bad taste in his mouth. Eventually, he believed that a pocket of poison has been implanted in his teeth by his dentist, and that he could bite himself and die. Further decline and clinical evolution pointed toward early manifestations of Alzheimer's Dementia. Patients suffering from psychotic depression may also, report the illusion of bad taste in their mouth (17).

Peduncular hallucinations: They originate from lesions of the mid-brain tegmentum. They may be elaborated and complex, rich in color, and depict landscapes, familiar faces, buildings, or lilliputian visions. Feeling tone may be absent, and the patient witnesses them with calm amusement.

Auditory and Vertiginous Hallucinations:
1.- Auditory: Stimuli of the transverse gyrus of Heschl of the temporal lobe, may elicit auditory events. Sacks (18) quotes on Dimitri Shostakovich, the Soviet composer, who reportedly had a metallic shell fragment in the temporal horn of his left ventricle. He said "since the fragment has been there, each time [I lean] my head to one side, I can hear music - different each time!" Apparently he would use this method while composing, producing melodic models for his symphonies.

2.- Vertiginous: Meniere's disease is the cause of severe kinesthetic hallucinations , accompanied by nausea, dizziness, and malaise. It may be also have tinnitus, often described as "chirping", or as the sound of crickets. This must be clinically differentiated from acoustic neuroma, vertebro-basilar artery syndromes, and other posterior fossa entities.

Autoscopic hallucinations: These are a blend of visual and proprioceptive hallucinations. Lhermitte has defined them as "the visual hallucination of the self" (19). In these cases, the vision is of one's double, like in a mirror, sometimes repeating one's gestures, and on occasions busy with other activities, a veritable doppelg„nger (6). They may be secondary to hypnopompic hallucinations, migraine, seizure disorders, delirium, encephalitis, post-concussion syndrome, or even non-neurological events such as: transcendental meditation, mystic events, use of hallucinogens, and near death experiences.

Sleep Disorders. Have shown a variety of perceptual disturbances.

1.-Narcolepsy-Cataplexy (Gelineau): Aldrich (20) has reviewed the syndrome and reports the symptomatology of hypnagogic hallucinations (before falling asleep), sleep paralysis, and cataplexy sometimes triggered by a strong emotion or during a laughing attack. He believes these phenomena are a dissociated manifestation of REM Sleep, with an increased excitability of the giant cells of the pontine-reticular formation that allow visions to intrude into wakefulness.

Mellman and co-authors (21) reported two PTSD patients who experienced sleep disturbances and recurrent daytime hallucinations. Further studies confirm these patients suffered from narcolepsy as well. They assert that the content of PTSD symptoms and narcolepsy tended to dissociate, and that the PTSD symptomatology remitted while narcolepsy persisted and progressed.

Hypnopompic hallucinations: Siegel (22) reports once being overwhelmed by a very vivid hypnopompic vision (when waking up). He had a "sense of pressure in his chest from a being, talking in reverse, rendering him unable to move". He compares the experience, to the ones reported in medieval religious literature as a succubus, (a she-devil), versus incubus (a he- devil).

Variant Angina. A 67 year old WWII veteran had a repeated hypnopompic vision of his platoon fighting toward a Japanese machine-gun nest. At the end of his dream, he had been shot in the chest and experienced a tearing, excruciating pain. He would wake up with tachycardia, cold sweats, and a sense of impending doom. After further cardiovascular evaluation, including challenge tests, he was diagnosed as having a Prinzmetal variant angina. This coincides with other clinical observations of ischemic episodes while awakening from nightmares (23).

Sleep Apnea: Another veteran, (24) seen by us had repeated complaints of mild memory impairment, restless sleep, loud snoring and sleep paralysis. He had a repetitive frightening hallucinations of a dead former girlfriend, "with a long gown, a dagger in her hand, and transparent like smoke". He experienced substantial improvement of his Sleep Apnea after being placed on protriptyline, losing 40 pounds, and having an uvulo-palato-pharyngoplasty and adeno-tonsillectomy.

Migraine attacks can be the cause of a variety of perceptual distortions. Most frequently though, the so called, "fortification spectra" hallucinations (teichopsia) are seen. They may show as irregular, colored, shimmering, edged, scintillating crescents, developing close to the center of the visual field. Sacks (18) believes that the visions of St. Hildegarde, a 12th century mystic, were typical migrainous hallucinations. Patients with classic migraine (25) suffer from perfusion changes either in the retina or in the visual pathway. Therefore, hallucinations of various geometric shapes, zigzag, or turrets can be seen. Rarely migraine can produce an upside-down vision of an observed object.

The Alice in Wonderland syndrome has been recently reported (26). It involves hallucinatory feelings of change in the body image. One migrainous patient reported " I get all tired out from pulling my head down. [It feels] like a balloon, my neck stretches and my head goes up to the ceiling". LSD users and children suffering from Epstein-Barr virus infection have reported similar symptoms.

Experimental stimulation of the cortex: Penfield (27), while operating on epileptic patients at the Montreal Neurological Institute (MNI), stimulated various areas of the cortex. These were cooperative, fully conscious patients during the neurosurgical procedure, and could give accurate descriptions. He was able to elicit vivid imagery of what appear to have been previous, trivial life events. In the operating room, patients reported voices of friends, songs heard long ago, or pleasant, nostalgic reveries of youthful gatherings. He postulated that "somewhere in the brain of each of us there is a continuous ongoing record of the stream of consciousness, from birth to death" (28).

IV) Hallucinations of medico-surgical aetiology

a).- Auditory:

Rarely, some medical entities such as diabetes mellitus, multiple sclerosis, serous otitis media and intra-otic foreign bodies can generate unusual sounds, clicks, murmurs, roars, humming, buzzing or whizzing as was reported by Coleman back in 1894 (29).

b).- Visual

a) Entoptic hallucinations are related to lesions or abnormalities somewhere within the visuo-neural pathways. Roberts (11) has mentioned the post-cataract surgery delirium called "Black Patch disease". New surgical techniques have made its occurrence obsolete. Recently Holroyd et al (30) reported visual hallucinations in patients with macular degeneration with the associated risk factors of living alone, history of stroke and bilateral worsening of visual acuity. This points to a dual etiology of sensory deprivation, and decreased cortical inhibition.

b) Charles Bonnet's syndrome is a clinical entity of the elderly, first described by the Swiss naturalist, as an account of the visual hallucinations experienced by his grandfather. He described them as "amusing and magical visions, coexisting with reason" (31). It is now defined as a persistent recurrent visual hallucinatory phenomenon of a pleasant nature, with a clear state of consciousness, compelling, but seen by the patient as unreal. It is associated with ocular pathology, and tends to be "remarkably crisp and detailed, and at times lilliputian".

V) Hallucinations and illusions related to environmental aetiologies

I.- Auditory

Some veterans who were under continuous enemy fire, or who served in heavy artillery units complain of permanent bilateral noises, and tinnitus. The frequent exposure to high decibel sounds as in heavy metal rock bands, percussion instruments, and jackhammers may produce persistent noises once the stimulus has ceased. The incessant rattle of a train's wheels may eventually sound like rhythmic, illusory, repetitive phrases.

II.- Visual

Mirages are visual illusions such as those seen while driving and seeing wet pavement at a distance. They are due to a combination of individual factors and the reflection of light through different densities of heated air. Continuous work with computer and TV monitors may bring flickering in the visual fields.

VI) Pseudohallucinations

They have been defined as hallucinations that the patient knows to be such (1). Although the perception is rather vivid and crisp, the patient has the insight that it has no external foundation. Therefore, its primary characteristic is the awareness of the unreality of the hallucinatory experience. The cases with obtunded sensorium portend a worse prognosis.

a) Radio-reception. A 35 year old Vietnam combat, veteran (32) started to complain of depression, headaches, and hearing blurred voices and music. Skull X-rays showed shrapnel metallic densities in the soft tissues and cranial bones of the left parieto-occipital region. His perception of voices and music were matched with stations in the AM broadcast band, and consistently identified the same station in the 560 Khz range. His radio- reception involved the metal implant diode rectification of the radio signal, and its bone transmission to the auditory apparatus. Other cases of broadcast reception due to dental work have been reported as well.

b) Virtual reality. A contemporary equivalent of the psychedelic culture has emerged with the use of "high-tech" interactive electronic gadgetry. These self-induced illusions of an alternate, parallel world may seem authentic and propel a compelling imagery. There is a potential for dependency in these pseudo-hallucinatory experiences of cyberspace.


Hallucinations and illusions, are part of a continuum of perceptual disturbances with manifold variations. They may entail idiosyncratic forms of bodily communication, or transfer of information from within or without. In the context of mental illness they are supported by thought disorder and crystallized delusional system. In states of delirium, drug intoxications, or neurological dysfunction, they may be perceived as transient, bewildering, unreal phenomena.

For the proper clinical management of a hallucinating patient, it is of the utmost importance to rule out a medical or neurological entity, perhaps an adverse drug reaction or use of hallucinogens within the context of a culturally validated phenomena. A psychiatric diagnosis should only be arrived at after a judicious evaluation of the phenomenology of the hallucinatory phenomena, circumstances in which they appear, and concomitant symptoms. In some instances, a psychiatric consultation may be in order.


1.- Hinsie L and Campbell R. Psychiatric Dictionary. Fourth Edition, Oxford University Press. New York, 1970.

2.- American Psychiatric Association: Diagnostic and Statistical Manual of Mental Disorders, Third Edition, Revised, American Psychiatric Association Press. page 113, Washington DC, 1987.

3 .-Roberts, D. Geronimo. National Geographic. 182: 46-71, October 1992.

4.- Solomon PH, Leiderman HE, Mendelson JA et al. Sensory Deprivation: A Review. Am. J. Psychiatry. 114: 357-363, 1957.

5.- Sacks OL. Seeing Voices: A Journey intro the world of the deaf, page 7, Univ. of California Press. Los Angeles, 1989.

6.- Boza RA, Milanes FE, Hanna GS and Trujillo MO. Psychiatric symptoms associated to Parietal Lobe Dysfunctions. Resident & Staff Physician. 39 (1):59-68, January 1993.

7.- Cohen, SI. Flashbacks. Drug Abuse & Alcoholism Newsletter. 6: No. 9, November 1977.

8.- Hoffman AL. The Discovery of LSD and subsequent investigations on naturally occurring hallucinogens. - Discovery in Biological Psychiatry -. page 91, Ayd FR & Blackwell BA, Eds. J.B. Lippincott Co. Philadelphia, 1970.

9.- Sifton DA and Mehta MU. PDR's Drugs Interactions and Side Effects System. Computer Database. Medical Economics Data. Release 3.1. Update September 1992.

10.-Lessell SI. Visual hallucinations and related phenomena. Weekly Update: Neurology and Neurosurgery. 2 (6): 48-54. Biomedia. Princeton, New Jersey, February 1980.

11.-Roberts JE. Differential Diagnosis in Neuropsychiatry. Chapter 16, Disorders of Perception, pages 258-271, J. Wiley & Sons. New York, 1986.

12- MacDonald, Critchley: "The Parietal Lobes." London. Hafner Press, 1953.

13.-Johnson GE and Anton RA. Delusions of parasitosis: differential diagnosis and treatment. Southern Medical Journal. 78 (8): 914-918, August 1985.

14.-Sigell LE, Kappa FR, Fusaro GR, et al. Popping and snorting volatile nitrites: A current fad for getting high. Am. J. Psychiatry. 135 (1): 1216-1218, Oct 1978.

15.-Alajouanine, T. Dostoiewsky's Epilepsy. Brain 86: 209-218 June 1963.

16.-Penrose RI and Wilder JO. Epilepsy: The Seizure - Variations on a Theme. pages 30-32. Neurology Series. F.A. Davis Co. Philadelphia, 1968.

17.-Carter JE. Visual, Somatosensory, Olfactory and Gustatory Hallucinations. The Interface of Psychiatry and Neurology. Psychiatric Clin. of N. America. 15 (2): 347-358, June 1992.

18.-Sacks, OL. The Man who mistook his Wife for a Hat: Chapter 15. Reminiscence, page 134, Chapter 20. The visions of Hildegard, page 160. Summit Books, New York, 1985.

19.-Lhermitte, JE. Visual hallucinations of the self. British Medical Journal. 1:431-434, March 3, 1951.

20.-Aldrich MI. Review Article: Narcolepsy. NEJM. 323 (6): 389-394. August 9, 1990.

21.-Mellman TO, Ramsay EU, and Fitzgerald ST. Divergence of PTSD and Narcolepsy associated with military trauma. Journal of Anxiety Disorders. 5:267-272, 1991.

22.-Siegel RO. Fire in the Brain: Clinical Tales of Hallucinations. Penguin Books. New York, 1992.

23.-Otsuka KO, Yanaga TA and Watanabe HA. Variant Angina and REM Sleep. American Heart Journal. 115: 1343-1345. June 1988.

24.-Boza RA, Trujillo MO, Millares SY, et al. Sleep Apnea and associated neuropsychiatric symptoms: A case report. VA Practitioner 1 (8):43-45, August 1984.

25.-Selby, GE. Migraine and its Variants. In Current Diagnoses - 5 Ed., page 961. Conn HO and Conn RE. W.B. Saunders & Co. Philadelphia, 1977.

26.-Rolak LO. Literary neurologic symptoms: Alice in Wonderland. Arch. Neurology. 48 (6): 649-651, June 1991.

27.-Penfield WI and Jasper HE. Epilepsy and the functional anatomy of the human brain, pages 453-461. Little Brown Co. Boston, 1954.

28.-Milner BR. In Memory Mechanisms. From Wilder Penfield: His Legacy to Neurology. Canadian Med. Journal. 116: 1365-1377, 1977.

29.-Colman WS. Hallucinations in the sane associated with local organic disease of the sensory organs. British Med. Journal 1 (1894): 1015-1017. May 12, 1894.

30.-Holroyd S, Rabins P, Finkelstein D, et al. Visual hallucinations in patients with macular degeneration. Am. J. Psychiatry. 149 (12): 1701-1706, December, 1992.

31.-Gold KE and Rabinds PE. Isolated Visual Hallucinations and the Charles Bonnet Syndrome: A Review of the Literature and Presentation of Six Cases. Comp. Psychiatry 30 (1): 90-98, January/February 1989.

32.-Boza RA and Liggett ST. Pseudohallucinations: Radio-reception through shrapnel fragments. Am. J Psychiatry. 138 (9): 1263-1264, September 1981.


Click on these buttons to visit our journals
Return to Psychiatry On-Line Return to Dentistry On-Line Return to Vet On-Line Return to GP On-Line Link to Pharmacy on-Line Return to Anaesthesia On-Line Return to Medicine On-Line Return to Family Medical Practice On-Line

All pages copyright ©Priory Lodge Education Ltd 1994-1999.

Last amended: