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Introduction The corpus callosum serves the essential role of relaying cognitive information between the homologous regions in the left and the right hemispheres of the brain. Cognitive impairment is a core dysfunction of schizophrenia, but much of its pathophysiology is unknown. The aim of this study was to elucidate the association between microstructural abnormalities of the corpus callosum and cognitive dysfunction in schizophrenia. Methods We examined stepwise multiple regression analysis to investigate the relationship of the fractional anisotropy (FA) of callosal fibers in each segment with z ‐scores of each brief assessment of cognition in schizophrenia subtest and cognitive composite score in all subjects (19 patients with schizophrenia [SZ group] and 19 healthy controls [HC group]). Callosal fibers were separated into seven segments based on their cortical projection using tract‐specific analysis of diffusion tensor imaging. Results The FA of callosal fibers in the temporal segment was significantly associated with z ‐scores of token motor test, Tower of London test, and the composite score. In the SZ group, the FA of callosal fibers in the temporal segment was significantly associated with the z ‐score of the Tower of London test. In addition, the FA of callosal fibers in temporal segment showed significant negative association with the positive and negative syndrome scale negative score in the SZ group. Compared to the HC group, the FA in temporal segment was significantly decreased in the SZ group. Conclusion Our results suggest that microstructural abnormalities in the callosal white matter fibers connecting bilateral temporal lobe cortices contribute to poor executive function and severe negative symptom in patients with schizophrenia.

SummaryObjectiveElucidation of abnormal connections throughout the whole brain is necessary to understand temporal lobe epilepsy (TLE). We examined abnormalities in whole‐brain white matter integrity and their relationship with duration of illness in patients with TLE.MethodsThe subjects were 15 patients with TLE and 17 healthy controls. Mean duration of illness in the TLE group was 21.6 years. Tract‐based spatial statistics (TBSS) were used for diffusion tensor imaging (DTI) analysis. Four diffusion tensor metrics, that is, fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were calculated and then examined for differences between the TLE and healthy control groups. We also examined for correlations between DTI parameters and duration of illness in the TLE group.ResultsIn the TLE group, compared with the healthy control group, FA was reduced, and MD and RD were increased, not only in the limbic and temporal lobe regions and their directly connecting regions in both hemispheres, but also in remote white matter regions. Duration of illness showed a significant negative correlation with mean whole‐brain FA and a significant positive correlation with both mean whole‐brain MD and RD. Brain regions showing correlation between disease duration and DTI metrics also extended to the limbic area and its connecting regions, and to remote white matter regions.SignificanceThe results of this study suggest that widespread abnormalities in white matter integrity in patients with TLE are associated with long‐term disease.

Background:In bipolar disorder (BD), reduced white matter (WM) integrity in the corpus callosum has been reported, but its detailed localization difference has not been clarified. In this study, we examined fiber integrity in 7 segments of the corpus callosum and their relationships with clinical symptoms in BD.Methods:Patients with BD (BD group, n = 17) and age-matched healthy controls (HC group, n = 24) were examined using diffusion tensor imaging tractography. The corpus callosum was divided into 7 segments (orbital frontal, anterior frontal, superior frontal, superior parietal, posterior parietal, temporal, and occipital) based on their cortical projection zones, and fractional anisotropy (FA) value of each segment was estimated. Differences in FA of each segment between the groups were examined using ANOVA with repeated measures. Correlations between FA of each segment and clinical symptoms (HAM-D, YMRS) were assessed using Spearman's rank correlation test in the BD group.Results:The BD group showed reduced FA in the orbital frontal, superior frontal, and posterior parietal-callosal segments compared to the HC group. In addition, the BD group showed a significant negative correlation between FA in the orbital frontal-callosal segment and HAM-D scores.Conclusions:Our results suggest that WM integrity in the anterior part of the corpus callosum is reduced in BD and that orbital frontal-callosal disintegrity may be related with severity of bipolar depression.