Investigation of differences on cortical connectivity between patients with major depressive disorder and normal subjects using MR diffusion tensor imaging

Functional and structural neuroimaging studies of major depression disorder (MDD) have identified neurophysiologic abnormalities in multiple areas of the prefrontal cortex, the insula, the amygdale and the related parts of the striatum and thalamus. The functional knowledge of MDD was mainly obtained from the fMRI and PET studies, which reveal the local differences in blood oxygenation and metabolism of the specific neurotransmitters, respectively. For the structural studies, the T1-based and DTI (diffusion tensor image)-based studies, which defined the abnormalities in cortical thickness and the integrity of the white matter, respectively, were commonly used. However, most of these studies only addressed the local differences compared to the normal subjects and were limited to provide the overall associations of the cortical connectivity within the patient group. In this study, we employed the DTI-based fiber bundle tracking technique along with the graph theoretical analysis to investigate the difference of cortical connectivity between the patients with MDD and the normal group from both the global (mean properties for all regions) and local (region-by-region) aspects. Out results concluded that: 1) there were no globally but locally significant difference between two groups, specifically, the increase of the local connectivity in parietal and occipital lobes to compensate the decrease of the connectivity in frontal and temporal lobe; 2) the connection strength from left insula to left superior temporal pole was stronger in normal group than that in MDD group; 3) the connection strengths from left putamen to left triangular inferior frontal gyrus and left precuneus, were stronger in patient group than that in normal group.