hallucination

Hallucination is a perception-like experience that occurs without external stimuli, is typically vivid and involuntary, and is perceived as real by the person. Hallucinations can involve any sense but most commonly affect hearing or vision. They are distinguished from illusions, which are misinterpretations of real stimuli.

Common modalities include auditory, visual, tactile, olfactory, and gustatory experiences. Hallucinations may be simple (a single sensory percept) or complex (voices, formed images, or scenes). Sleep-related experiences, such as hypnagogic (upon falling asleep) and hypnopompic (upon waking) hallucinations, can occur in healthy people but may also be associated with sleep disorders or other conditions.

Causes and contexts are diverse. They occur in psychiatric disorders such as schizophrenia and bipolar disorder with psychotic features; neurologic conditions including dementia, epilepsy, Charles Bonnet syndrome; delirium, migraines, and brain lesions; as well as medical illness, substance use or withdrawal (alcohol, cannabis, stimulants, hallucinogens), and severe sleep deprivation or extreme stress.

Diagnosis relies on clinical assessment and history, with attention to delirium, intoxication, or neurologic disease. Differential diagnosis includes pseudohallucinations and misperceptions from sensory loss. Investigations may include neurological exam, cognitive testing, and, when indicated, imaging or electroencephalography.

Treatment targets the underlying cause. Antipsychotic medications may be used for psychotic disorders; addressing sleep, substance use, caregiver support, and safety planning are important. In many cases, hallucinations improve with treatment of the underlying condition, though some may persist.