Abstract
Convergent evidences have demonstrated a variety of regional abnormalities of asymmetry in bipolar disorder (BD). However, little is known about the alterations in hemispheric topological asymmetries. In this study, we used diffusion tensor imaging to construct the hemispheric brain anatomical network of 49 patients with BD and 61 matched normal controls. Graph theory was then applied to quantify topological properties of the hemispheric networks. Although small-world properties were preserved in the hemispheric networks of BD, the degrees of the asymmetry in global efficiency, characteristic path length, and small-world property were significantly decreased. More changes in topological properties of the right hemisphere than those of left hemisphere were found in patients compared with normal controls. Consistent with such changes, the nodal efficiency in patients with BD also showed less rightward asymmetry mainly in the frontal, occipital, parietal, and temporal lobes. In contrast to leftward asymmetry, significant rightward asymmetry was found in supplementary motor area of BD, and attributed to more deficits in nodal efficiency of the left hemisphere. Finally, these asymmetry score of nodal efficiency in the inferior parietal lobule and rolandic operculum were significantly associated with symptom severity of BD. Our results suggested that abnormal hemispheric asymmetries in brain anatomical networks were associated with aberrant neurodevelopment, and providing insights into the potential neural biomarkers of BD by measuring the topological asymmetry in hemispheric brain anatomical networks.
Highlights
The human brain is structurally and functionally asymmetrical or lateralized (Watkins et al, 2001; Toga and Thompson, 2003)
Post hoc analysis indicated that this interaction resulted from a significant rightward trend in global integration (P = 0.001) and a significant leftward trend in the characteristic path length (P = 0.003), the normalized clustering coefficients (P < 0.001), and small-world architecture (P < 0.001) in normal controls and a symmetrical trend in patients with bipolar disorder (BD)
Using the DTI deterministic tractography method and graph theory, the current work evaluated the hemispheric effects on brain anatomical networks in patients with BD
Summary
The human brain is structurally and functionally asymmetrical or lateralized (Watkins et al, 2001; Toga and Thompson, 2003). Convergent studies on BD have showed abnormal asymmetries in WM (Bruno et al, 2008; Kafantaris et al, 2009; Wessa et al, 2009; Mahon et al, 2013), for example, less WM volume within the left frontal lobes, the rightward WM in orbital frontal. These results indicated that the alteration in WM asymmetries have been proposed as a key factor in the manifestation of BD symptoms
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