Hallucinations

Definition

Hallucinations can be defined as conscious abnormal sensory perceptions that do not have a source in the outside world. Hallucinations can involve one or more senses, including visual, auditory, gustatory, olfactory, or tactile. People who experience hallucinations report experiences such as seeing things that aren't there, hearing voices that no one else can hear, feeling that there is something crawling on their skin, smelling things that no one else can smell, or tasting things that other people cannot taste.

In one study, Johns and colleagues found that prevalence of hallucinations in a community sample ranged from 2% to 10%. There is currently no evidence that hallucinations occur more frequently in some racial or ethnic groups than in others, and gender does not appear to affect the presence or frequency of hallucinations.

Disorders Associated with Hallucinations

Hallucinations are associated with numerous disorders, illnesses, and states. Currently, there does not appear to be a single underlying cause that can explain all types of hallucinations. Several explanations and hypotheses have been put forth for various disorders, but to date, the causes of hallucinations are not completely understood.

Hallucinations are most commonly associated with schizophrenia, a mental illness characterized by disordered perceptions, thoughts, and behaviors. According to the National Institute of Mental Health, approximately 75% of individuals with a diagnosis of schizophrenia experience auditory hallucinations, visual hallucinations, or both. The auditory hallucinations may be command hallucinations, in which the person hears voices ordering him or her to do something.

Other disorders are that are less frequently associated with hallucinations include eye disorders such as macular degeneration or glaucoma; high fever, particularly in children and the elderly; late-stage Alzheimer's disease; migraine headaches; intoxication or withdrawal from alcohol or drugs; severe medical illness such as liver or kidney failure or brain cancer; severe mood disorders such as bipolar disorder and depression; post traumatic stress disorder; and temporal lobe epilepsy. In addition, hallucinations are also associated with normal sleep-wake cycles. Approximately one third of adults experience hypnagogic hallucinations, which occur as a person passes from wakefulness into sleep; another 10% to 12% of adults report hypnopompic hallucinations, which occur as the person is waking up.

Hallucinations and Violence

The relationship between hallucinations and violent behavior has been the subject of debate. Some research has found a modest positive relationship between hallucinations and violence, whereas other studies found no immediate relationship. Dale E. McNeil and colleagues studied the relationship between command hallucinations and violence in a sample of 130 inpatients who were diagnosed with schizophrenia. They found that 30% of the inpatients reported that they had experienced command hallucinations to hurt someone else in the past year, while 22% of the patients reported that they complied with those command hallucinations. These findings suggest that patients who experienced command hallucinations were almost twice as likely to engage in violent behavior as patients who did not experience command hallucinations. Other studies have reported compliance for command hallucinations of violence ranging from 39.2% to 88.5%. Compliance with command hallucinations has been found to be related to whether or not the person recognizes the hallucinated voice, with those recognizing the voice being more likely to obey the command.

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