The point of rarity in brain structure and function that separates the 2 major psychotic disorders--schizophrenia and bipolar disorder--is presently unknown. The aim of this study is to combine surface anatomical and functional imaging modalities to quantify the integrity of cortical connectivity in pursuit of the neural basis of the Kraepelinian "line of divide." We tested the hypothesis that multimodal brain regions show overlapping abnormalities in both disorders, while schizophrenia-specific defects are likely to be localized to sensory processing regions. Cortical folding patterns (gyrification) and functional connectivity hub architecture (degree centrality) were studied in a sample of 39 subjects with established schizophrenia, 20 subjects with psychotic bipolar disorder, and 34 healthy controls. We observed a significant difference between the 2 groups in both gyrification and functional connectivity of the visual processing regions. Further, the aberrant functional connectivity of the visual processing regions predicted persistent symptom burden better than the diagnostic information. Using a spatial similarity analysis, we observed that the degree of overlap between the 2 disorders was small (25%) for changes in cortical gyrification and modest (51%) for changes in functional connectivity measured during a cognitive task (n-back). In conclusion, our results suggest that prominent unimodal sensory processing deficits are more likely to be present in schizophrenia than in bipolar disorder. Further, connectivity-based neuroimaging measures appear to be better indicators of diagnostic discontinuity than the symptom-based clinical information.
Keywords: Kraepelinian; bipolar disorder; gyrification; insula; schizophrenia; visual processing.