[The neurobiology of hallucinations]

Although hallucinations are among the cardinal features of schizophrenia, the mechanisms underlying these symptoms have not been fully understood yet. In this review our objective is to summarize the studies about the neurobiology of auditory hallucinations in schizophrenia and discuss their significance for understanding schizophrenia.

This is a retrospective literature review and the relevant studies within the last 10 years are included. For this purpose Pubmed search engine and 'hallucination, schizophrenia, neurobiology' key words are used.

Hallucinations cause sensory modality specific activation in cerebral areas involved in normal sensation. A disturbance in perception of speech seems to have a central role in occurrence of auditory hallucinations. Anatomically, auditory hallucinations appear to involve primary and association cortices, Broca's and Wernicke's areas, subcortical, paralimbic, limbic regions, ventral striatum and thalamus. Furthermore they are suggested to be associated with the dysmodulation of the information flow from ventral striatum to thalamus and cortex caused by increased dopaminergic activity in mesolimbic pathway.

The validity of the models which are proposed to explain neurobiology of hallucinations in schizophrenia should be tested by new studies. The difficulties regarding the assessment and measurement of subjective mental phenomena are important impacts in studying and understanding the neural correlates of hallucinations. Functional neuroimaging, cognitive and molecular biological studies will hopefully enhance our knowledge about this disease.