Tract-based structural and functional connectivity abnormalities in bipolar I disorder

Bipolar disorder (BP) is a complex mental illness with poorly understood neural underpinnings. This study aimed to investigate abnormalities in the structural and functional connectivity (FC) of white matter (WM) tracts in BP.

Diffusion magnetic resonance imaging (MRI) and resting-state functional MRI data were obtained for 56 patients with BP subtype I (BP-I) and 40 healthy controls (HCs). A total of 72 WM tracts and their corresponding start and end regions were automatically segmented based on diffusion image. The mean diffusivity (MD) and mean fractional anisotropy (FA) of each tract were calculated as proxies of tract-based structural connectivity. FC between the start and end regions of each tract was calculated as a proxy of tract-based FC. The analysis of covariance (ANCOVA) was used to compare the mean MD, FA, and FC values between groups, with multiple comparison correction based Hommel approach.

Compared to the HCs, BP-I patients showed significantly lower FA in the corpus callosum, right and left cingulum, and right superior longitudinal fasciculus III as well as higher MD in the corpus callosum and commissure anterior. Among the tracts with abnormal structural connectivity, only the right SLF-III demonstrated significantly lower FC in the BP-I group than in the control group.

BP-I is associated with altered structural connectivity and FC in specific WM tracts, which provides insights into the pathophysiology of this disorder. More research is required to understand the diagnostic and therapeutic implications of these results.