Hallucinations and Altered Perceptions

Hallucinations in Healthy People

Healthy people can experience hallucinations. For instance, the hearing of a family member's voice is not uncommon among recently bereaved people. These hallucinations become less frequent and cease over weeks or months. They are comforting and benign.

Some people take hallucinogenic drugs, such as LSD or mescaline, with the clear intention of inducing hallucinogenic experiences. Hallucinations may also occur with some medically prescribed drugs, for example, the anesthetic drug ketamine, or the drug used in the treatment of

Parkinson's disease, levodopa. In drug withdrawal states, particularly withdrawal from alcohol, hallucinations are common.

Visual hallucinations have been reported during sensory deprivation in healthy individuals, either as a result of solitary imprisonment (“prisoner's cinema”), or during prolonged blindfolding. Hallucinations can occur in pilots during long night flights. Hallucinations also occur during snowstorms, suggesting that absence of patterned stimulation is more likely to produce visual hallucinations than is light deprivation.

Hallucinations in Mental Disorders

Auditory hallucinations usually mean hearing voices. However, nonverbal auditory hallucinations do occur and include clicking and mechanical noises, muttering or mumbling, and music. In musical hallucinations, the patient often hears a complete piece of music. Auditory hallucinations are most common in psychotic disorders such as schizophrenia, but can occur in mood disorders, organic mental disorders, and drug-induced states. Auditory hallucinations occasionally occur in the elevated phase of bipolar disorder and in severe (psychotic) depression.

Visual hallucinations can be classified into simple and complex hallucinations. Simple hallucinations mostly consist of dots, lines, geometric shapes, and moving patterns. Complex hallucinations include the occurrence of other people, animals, and more rarely objects such as cars or tables. Visual hallucinations may occur with such brain disorders as [Page 476]tumors, multiple sclerosis, and dementia. They occur more frequently than auditory hallucinations in the organic mental disorders. In some types of epilepsy, visual hallucinations may form complex scenes. In schizophrenia, visual hallucinations are often indistinct or distinct figures, often humanoid, standing to one side of the patient.

Tactile hallucinations include the experience of being touched, or of a crawling sensation under the skin. These are common in drug withdrawal states, but may occur in schizophrenia. Somatic hallucinations are the sensation of things happening inside the body, such as organs moving from one part of the body to another. These are rare, but may occur in schizophrenia. Gustatory hallucinations, the hallucinations of taste and smell, are common in such medical conditions as epilepsy, but can rarely occur in schizophrenia.

Hallucinations in Other Medical Conditions

In migraine, a common condition involving people without a mental disorder, visual hallucinations are usually experienced just before a migrainous attack (“aura”). Sometimes the aura can occur in the absence of headache. The percepts during the migraine aura take the form of scintillating, jagged lines, called migraine fortification spectra, which involve one half of the visual field and expand from the central field toward the periphery. The specific evolution in time of the percepts occurring during the migraine aura suggests that they might be related to biochemical changes that invade portions of the topographically organized visual cortical areas (“spreading depression”). Migraineurs are believed to show deficient cortical inhibitory processes.

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