T169. SEMANTIC PROCESSING IN RELATION TO ANATOMICAL INTEGRITY OF THE VENTRAL LANGUAGE STREAM IN SCHIZOPHRENIA SPECTRUM DISORDERS

BACKGROUND: Semantic processing anomalies, clinically reflected by disorganized speech are a core symptom of schizophrenia. In the light of accumulating evidence on its prominent role in semantic processing, aberrant structural integrity of the ventral language stream may reflect impaired semantic processing in schizophrenia spectrum disorders (SSD). METHODS: Comparison of white matter tract integrity in SSD patients and healthy controls using diffusion tensor imaging combined with probabilistic fiber tractography. For the ventral language stream, we assessed the inferior fronto-occipital fasciculus [IFOF], inferior longitudinal fasciculus, and uncinate fasciculus. The arcuate fasciculus and corticospinal tract were used as control tracts. In SSD patients, the relationship between semantic processing impairments and tract integrity was analyzed separately. Three-dimensional tract reconstructions were performed in 45/44 SSD patients/controls (“Bern sample”) and replicated in an independent sample of 24/24 SSD patients/controls (“Basel sample”). RESULTS: Multivariate analyses of fractional anisotropy, mean, axial, and radial diffusivity of the left IFOF showed significant differences between SSD patients and controls (p<0.001, ηp2=0.23) in the Bern sample. In SSD, axial diffusivity of the left IFOF was inversely correlated with semantic processing impairments (r=-0.579, p<0.0001). In the Basel sample, significant group differences for the left IFOF were replicated (p<0.01, ηp2=0.29), while the correlation between axial diffusivity of the left IFOF and semantic processing decline (r=-0.376, p=0.09) showed a statistical trend. No significant effects were found for the dorsal language stream. DISCUSSION: This work provides direct evidence for the importance of the integrity of the ventral language stream, in particular the left IFOF, in semantic processing deficits in SSD.