Major depression can be regarded as a systemic neurobehavioral disorder resulting from dysfunction of the limbic-cortical networks. The cingulum bundle represents a major association fiber tract of those networks. The aim of our study was to determine the association of brain structural tissue markers of the cingulum bundle and cognitive function in patients with major depression.

Region-of-interest-based analyses of the middle-anterior and middle-posterior cingulum bundle fractional anisotropy (FA) and mean diffusivity (MD) using color-coded diffusion-tensor imaging and neuropsychological assessment in 14 patients with major depression.

FA of the middle-anterior and middle-posterior cingulum bundle was significantly correlated to the performance in a planning and divided attention task. Furthermore, MD of the middle-posterior cingulum bundle was significantly correlated to a planning task. There was no significant correlation between FA and MD of the cingulum bundle and selective attention or memory.

Brain structural tissue markers of the middle-anterior and middle-posterior cingulum bundle were found to be associated with executive functioning and divided attention in patients with major depression. Disconnection within the limbic-cortical networks may underlay cognitive dysfunction in major depression.

Bipolar disorder (BD) has been associated with altered brain structural and functional connectivity. However, little is known regarding alterations of the structural brain connectome in BD. The present study aimed to use diffusion-tensor imaging (DTI) and graph theory approaches to investigate the rich club organization and white matter structural connectome in BD.

Forty-two patients with unmedicated BD depression and 59 age-, sex- and handedness-matched healthy control participants underwent DTI. The whole-brain structural connectome was constructed by a deterministic fiber tracking approach. Graph theory analysis was used to examine the group-specific global and nodal topological properties, and rich club organizations, and then nonparametric permutation tests were used for group comparisons of network parameters.

Compared with healthy control participants, the patients with BD showed abnormal global properties, including increased characteristic path length, and decreased global efficiency and local efficiency. Locally, the patients with BD showed abnormal nodal parameters (nodal strength, nodal efficiency, and nodal betweenness) predominantly in the parietal, orbitofrontal, occipital, and cerebellar regions. Moreover, the patients with BD showed decreased rich club and feeder connectivity density.

Our results may reflect the disrupted white matter topological organization in the whole-brain, and abnormal regional connectivity supporting cognitive and affective functioning in depressed BD, which, in part, be due to impaired rich club connectivity.