Central auditory processing in schizophrenia

Auditory hallucinations represent a key symptom in schizophrenia, which severely disables the patient. "Hearing voices" in the absence of an external acoustic source is a form of speech mis-perception. In a psychotic episode, the voices heard are "inside the head", whereas the "person speaking" is localized "outside of the head". Since speech perception activates the left upper posterior part of the temporal lobe, a case could be made that auditory hallucinations are related to disturbance of speech perc eption, lateralized to the left temporal lobe. Lateralization of speech perception to the left temporal lobe can be studied experimentally in a dichotic listening (DL) paradigm. We predict that frequency of auditory hallucinations will go together with re duction or abolishment of a right-ear advantage in DL situation, accompanied by reduced neuronal activation in the vicinity of the STG/STS areas in the left hemisphere, as measured with fMRI. We further predict that patients with schizophrenia will lack t he ability to cognitively modulate processing of a speech signal by focused attention. This should be accompanied by reduced neuronal activation bilaterally in a fronto-parietal cortical network. In a second series of studies, we will study structural MR imaging, focused on grey matter volume reductions in the same areas. i.e. STG/STS areas. We predict that the reduction in neuronal activation in the fMRI studies will be accomanied by a corresponding loss of greay matter volume, and that this will be posi tively related to illness duration, i.e. suggesting a degenerative component in schizophrenia. First episode and chronic patients will be recruited from the BMH-Center. Hallucinations will be scored from the PANSS scale. Control subjects will be age, sex and education matched.