Altered frontal white matter asymmetry and its implications for cognition in schizophrenia: A tractography study

BACKGROUND: White matter (WM) alterations are well documented in schizophrenia. Abnormalities in interhemispheric fibers appear to account for altered WM asymmetry in the illness. However, the regional specificity (e.g., frontal versus occipital) of these alterations and their potential contribution to cognitive dysfunction in schizophrenia remain unknown. METHODS: Forty one patients with schizophrenia and 21 healthy controls (HC) underwent diffusion-weighted imaging on a 3 Tesla MRI machine. Tract-based spatial statistic (FSL) was used to assess whole brain differences in WM. Probabilistic tractography was performed in order to separately measure frontal and occipital WM tracts. Participants also completed tests of verbal memory and processing speed. Repeated measures analyses of covariance and Pearson correlation analyses were performed. RESULTS: A significant group x cerebral hemisphere interaction was found for fractional anisotropy (FA) (F((1,17)) = 7.03; p = .017; η(p)(2) = 0.29) and radial diffusivity (RD) (F((1,17)) = 4.84; p = .042; η(p)(2) = 0.22) in the frontal tract of patients versus HC. Healthy controls showed higher mean FA and lower mean RD in the left frontal tract compared to patients, who showed the opposite pattern. In patients with schizophrenia, mean FA and RD in the right frontal tract correlated with verbal memory (r = −0.68, p = .046; r = 0.77, p = .015). CONCLUSIONS: Asymmetric WM alterations were found in a frontal tract of patients with schizophrenia. Higher mean FA in the right frontal tract correlated with worse verbal memory performance, suggesting a possible contribution these brain changes to cognitive impairment in schizophrenia.