Cingulum bundle connectivity considering the double-layered cingulate cortex using diffusion-weighted MRI.

The cingulum bundle (CB) is a fasciculus in the white matter surrounded by the cingulate cortex, which is generally subdivided into the anterior, middle, and posterior parts based on their function and cytology. Interestingly, the cingulate cortex can also be divided into inner and outer layers based on their gross anatomy. Herein, we analyzed the CB pathway by considering the double-layered cingulate cortex using magnetic resonance (MR) tractography data. We used 7.0T diffusion-weighted MRI data from the Human Connectome Project dataset, from which 32 individual datasets were selected. Anatomical MR images in each dataset were parcellated into the cortical subdivisions automatically using the FreeSurfer software. The seed positions in both layers of the cingulate white matter (CWM) for fiber tracking were determined based on the parcellated MR image data. The cingulate cortex with double layers was found in 46.5% of the coronal section in the cingulate cortex's dorsal part, with many individual differences in the outer-layered CWM. Fiber extraction from each determined seed position in both layers of the CWM was carried out using the MRtrix software. The fiber tracking results indicated that the anterior and posterior areas demonstrate major cortical connectivity through the inner-layered CB and the superior area of the brain through the outer-layered CB. From the results, we designed a new CB connectivity model considering the double-layered cingulate cortex to provide a more organized insight into the function of CB function and its connectivity with the cerebral cortex.