![]() ![]() The 2 main language epicentres are the Wernicke area located in the posterior temporal and parietal cortex, which connects word meanings with objects and concepts, and the Broca area located in the inferior frontal gyrus, which is involved in sentence production. The middle temporal gyrus also contains association cortex responding to understandable speech. This is surrounded by secondary auditory association areas that are involved in identifying more complex auditory sequences like the phonetic features of speech (but not its meaning). To briefly summarize these, the primary auditory cortex, which is involved with the perception of pure tone and pitch, is located on the dorsal surface of the superior temporal gyrus. It might be expected that the basis for auditory hallucinations would be found in the brain regions known to subserve normal audition, language perception and language production. Patients with schizophrenia experiencing auditory hallucinations have been studied most often. Recently, neuroimaging technology has been used quite extensively in an attempt to understand the brain regions and circuitry involved in the generation of hallucinations. 6 For example, the complex visual hallucinations seen in Charles Bonnet syndrome are most often caused by damage to the visual system such as macular degeneration or lesions to the central nervous system pathway between the eye and the visual cortex. ![]() As a first approach to studying the mechanism of hallucinations, psychologically normal individuals with hallucinations due to lesions have been studied, and the lesion was generally found to be in the brain pathway of the sensory modality (e.g., auditory, visual, somatic) of the hallucination. How close are we to understanding the brain mechanisms responsible for hallucinations in psychotic disorders like schizophrenia? Among the various complex symptoms of psychotic disorders, it would seem that hallucinations might be a relatively discrete and precisely defined symptom, and therefore amenable to understanding the brain mechanisms involved. It should be noted, however, that it is unknown at present whether hallucinations are generated by similar mechanisms in patients and in healthy people. ![]() 5 The neurobiological basis of hallucinations has most frequently been investigated in patients with schizophrenia, although studies examining hallucinatory phenomena in healthy individuals may also be informative. 4 In healthy people, pseudohallucinations can even be generated at will by mild sensory deprivation for example, vivid dreamlike visual imagery can be induced in some individuals by placing 2 halves of a ping pong ball over the eyes and playing a recording of the sounds of a waterfall for several minutes. 2, 3 Transcultural influences may also affect the distinction between reality and imagination as well as the normalcy of visualizing images and ideas. ![]() 1 In the context of grief after the death of a spouse, one-third to one-half of bereaved spouses report hallucinations of the deceased. For example, data from 6 community survey studies in various countries indicate that 7%–30% of children and adolescents report experiencing hallucinations. However, hallucinations are not only associated with illness but can also occur in healthy individuals. They are a diagnostic feature of schizophrenia, occurring in an estimated 60%–70% of people with this disorder, with auditory hallucinations being the most common. Hallucinations are perceptions in the absence of an external stimulus and are accompanied by a compelling sense of their reality. ![]()
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