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< Supporting Evidence

Language Production in the Non-Dominant Hemisphere as a Potential Source of Auditory Verbal Hallucinations

Iris E. Sommer and Kelly M. Diederen
Brain, 2009, 132 (10): e124.

Excerpts:

In our data, activity during auditory verbal hallucinations was not confined to the right anterior insula, but extended into the posterior insula and Broca's homologue (Sommer et al., 2008). We hypothesized that activity of this large cortical region reflects the (unconscious) generation of language. Although the right inferior frontal and insular region is not a classical language area, there is evidence that this area has limited capacity for language production (Thiel et al., 2006; Voets et al., 2006). We hypothesize that the right inferior frontal-insular area is insufficiently inhibited in patients with auditory verbal hallucinations, leading to unintended 'ectopic' language production. A similar mechanism of a right hemispheric area generating 'ectopic speech' has been described in aphasia patients (Winhuisen et al. 2005). ...

The content and repetitive nature of the automatic utterances in aphasia patients, as well as the lack of voluntary control over these utterances, bear resemblance to auditory verbal hallucinations in schizophrenia patients (Gould, 1950). An obvious difference is that automatic utterances are spoken, while auditory verbal hallucinations are heard. However, before being heard, auditory verbal hallucinations are probably generated in speech production areas that may coincide with the source of automatic speech in aphasia. ...

The regions (Broca's homologue and the right insula) coincide with the areas that showed greatest activation during auditory verbal hallucinations in our analysis of 24 patients (Sommer et al., 2008). It could therefore be hypothesized that auditory verbal hallucinations result from 'release' language activity in the right inferior frontal area that is inhibited in the healthy brain.