Not on speaking terms: hallucinations and structural network disconnectivity in schizophrenia

Auditory verbal hallucinations (AVH) in schizophrenia have previously been associated with functional deficiencies in language networks, specifically with functional disconnectivity in fronto-temporal connections in the left hemisphere and in interhemispheric connections between frontal regions. Here, we investigate whether AVH are accompanied by white matter abnormalities in tracts connecting the frontal, parietal and temporal lobes, also engaged during language tasks. We combined diffusion tensor imaging with tract-based spatial statistics and found white matter abnormalities in patients with schizophrenia as compared with healthy controls. The patients showed reduced fractional anisotropy bilaterally: in the anterior thalamic radiation (ATR), body of the corpus callosum (forceps minor), cingulum, temporal part of the superior longitudinal fasciculus (SLF) and a small area in the inferior fronto-occipital fasciculus (IFOF); and in the right hemisphere: in the visual cortex, forceps major, body of the corpus callosum (posterior parts) and inferior parietal cortex. Compared to patients without current hallucinations, patients with hallucinations revealed decreased fractional anisotropy in the left IFOF, uncinate fasciculus, arcuate fasciculus with SLF, corpus callosum (posterior parts-forceps major), cingulate, corticospinal tract and ATR. The severity of hallucinations correlated negatively with white matter integrity in tracts connecting the left frontal lobe with temporal regions (uncinate fasciculus, IFOF, cingulum, arcuate fasciculus anterior and long part and superior long fasciculus frontal part) and in interhemispheric connections (anterior corona radiata). These findings support the hypothesis that hallucinations in schizophrenia are accompanied by a complex pattern of white matter alterations that negatively affect the language, emotion and attention/perception networks.