Abstract
Auditory verbal hallucinations (AVH) or “voices” are a characteristic symptom of schizophrenia, but can also be observed in healthy individuals in the general population. As these non-psychotic individuals experience AVH in the absence of other psychiatric symptoms and medication-use they provide an excellent model to study AVH in isolation. Indeed a number of studies used this approach and investigated brain structure and function in non-psychotic individuals with AVH. These studies showed that increased sensitivity of auditory areas to auditory stimulation and aberrant connectivity of language production and perception areas is associated with AVH. This is in concordance with investigations that observed prominent activation of these areas during the state of AVH. Moreover, while effortful attention appears not to be related to AVH, individuals prone to hallucinate seem to have an enhanced attention bias to auditory stimuli which may stem from aberrant activation of the anterior cingulated regions. Furthermore, it was observed that decreased cerebral dominance for language and dopamine dysfunction, which are consistently found in schizophrenia, are most likely not specifically related to AVH as these abnormalities were absent in healthy voice hearers. Finally, specific aspects of AVH such as voluntary control may be related to the timing of the supplementary motor area and language areas in the experience of AVH.
Highlights
In contemporary Western societies auditory verbal hallucinations (AVH) or “voices” are generally considered an aspect of disease
As the non-psychotic individuals with AVH showed increased rather than decreased psychophysiological measures of effortful attention, these results suggest that the decrease in EEG measures of effortful attention observed in schizophrenia patients is not related to the tendency to hallucinate
For an overview of trait studies on AVH see Table 2. In summary, these studies show that while decreased cerebral dominance for language and dopamine dysfunction are presumably not related to AVH, increased sensitivity of auditory areas to auditory stimulation and aberrant connectivity of language production and perception areas is associated with these hallucinations
Summary
In contemporary Western societies auditory verbal hallucinations (AVH) or “voices” are generally considered an aspect of disease (al-Issa, 1995). The first group of studies investigated the neural signature of AVH and revealed that AVH-related brain activation can be observed in frontal and temporoparietal language areas as well as in the parahippocampal region (Jardri et al, 2010; Kühn and Gallinat, 2010). Hearing and imagery did not correlate with significant anterior cingulated activation in the control group of non-hallucinators from which the authors concluded that inappropriate activation of this region may lead self-generated thoughts to be experienced as external It is, important to note that these results are not in line with the study by Linden et al (2011) who found a similar pattern of activation during imagery and hallucinations. As the non-psychotic individuals with AVH showed increased rather than decreased psychophysiological measures of effortful attention, these results suggest that the decrease in EEG measures of effortful attention observed in schizophrenia patients is not related to the tendency to hallucinate
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