Hallucination (redirected from Gustatory hallucination)

hallucination, false perception characterized by a distortion of real sensory stimuli. Common types of hallucination are auditory, i.e., hearing voices or noises and visual, i.e., seeing people that are not actually present. Hallucinations play a prominent role in schizophrenia and in the mania stage of bipolar disorder (see depression). They are also significant during withdrawal from various drugs, particularly depressants such as barbiturates, heroin, and alcohol (see delirium tremens), and under the influence of hallucinogenic drugs such as LSD, mescaline, and psylocybin. Hallucinations may occur in normal people under conditions of sensory deprivation, emotional stress, religious exaltation, or great fatigue.

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hallucination

Perception of objects, sounds, or sensations having no demonstrable reality, usually arising from a disorder of the nervous system or in response to certain drugs (see hallucinogen). Hallucinations are in many ways similar to dreams: they derive their content from perceptions known to memory, though these can be greatly transformed. Hallucinations can result when attention collapses from intense arousal due to extreme anxiety, fatigue, excitement, or other causes. They figure prominently in the diagnosis of schizophrenia.

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Hallucination

A perceptual experience in the absence of external stimulation. Hallucinations differ from illusions, which are changes in the perception of a real object. Hallucinations tend to fade with fixation or with attention to the content. Except for afterimages, which lie like a film over objects, hallucinations replace objects and object space. A hallucination is not objectlike in its realness. The conviction of reality is due to the loss of an object for comparison and the inability to disprove the image through other sensory modalities.

Hallucinations that are recognized as such by the experiencer include those resulting from sensory deprivation, drug use, and the phantom limb state. See Schizophrenia

Hallucinations may occur in a range of neurologic and psychiatric conditions, although they are usually considered hallmarks of schizophrenia. Delusional misidentification syndromes are a subtype of hallucinations and may also occur in neurological and psychiatric disease. For example, Capgras syndrome, which is commonly seen in schizophrenia, causes the individual to replace a familiar person (usually the spouse) with an imposter with the same or similar physical appearance. Frégoli syndrome is the delusional confusion of an individual as a familiar person in disguise.

Neurotransmitters are directly involved in the regulation of drug-induced and schizophrenic hallucinations, with many accounts pointing to the involvement of serotonin and dopamine. Therefore, it is possible to treat individuals with antipsychotic drugs that stabilize the chemical systems involved.

With localized damage to the brain, hallucinations are usually brief and intermittent, though in some cases, especially neurologic damage involving the brainstem, hallucinations can be chronic and sustained.

Physical input to the eyes and ears constrains and guides the construction of mental images, but the final result—the perception of an object or sound as a meaningful event occurring in the external world—also reflects very complex physiological processes. They begin in the brainstem, pass to the limbic system of the brain, and finally involve the temporal, parietal, and occipital areas of the cerebral cortex. Various types of hallucination are caused by disruptions that occur at different levels along that sequence of brain processes. See Cognition

At its earliest phase, damage to the upper brainstem produces peduncular (crepuscular) hallucinations of faces, torsos, and occasionally geometric patterns or landscapes near the viewer at the close of day. The images may be static and immobile or may change in content and affective tonality while being viewed. A smiling young boy, for example, may change into a scowling old woman. The hallucinations are often vivid and chromatic, and tend to be multimodal: they are seen, heard, and even touched, and occur over the entire visual field. Olfactory and gustatory images have also been described. Peduncular hallucinations are similar to the hypnagogic hallucinations that are experienced when falling asleep. See Sleep and dreaming

Neurologic damage involving limbic and temporal-lobe structures yields hallucinations of faces or formed scenes laden with meaning and affect. Changes in size (micropsia, macropsia) and shape (metamorphopsia) may occur. Déjà vu, derealization, and dreamy states are common. Auditory hallucinations are usually of speech or music. Microscopic (Lilliputian) and autoscopic (out-of-the-body) hallucinations also occur with temporal-lobe lesions. Exposure to a wide range of drugs and many psychiatric disorders, especially schizophrenia, can lead to hallucinations whose form suggests dysfunction involving limbic or temporal-lobe structures. See Psychotomimetic drug

Damage to the parietal lobe leads to illusory distortions of shape, size, and motion, whereas occipital lesions or stimulation—or migraine—gives elementary hallucinations of sparks, flames, lines, or simple patterns. These hallucinations share features with afterimages. Palinopsia, the hallucinatory persistence of an object after the viewer has turned away, is a form of pathological afterimagery. See Perception