Longitudinal observation of functional connectivity in the insular subregions, as a characteristic change for bipolar...

The structural changes of the insula have been confirmed to be a stable and characteristic change in bipolar disorder (BD). Moreover, the different insular subregions involve distinct functional activity patterns. Previous studies observing the insula as a whole region may obscure its subtle alterations. Therefore, a longitudinal investigation of functional connectivity (FC) changes in insular subregions may provide a new perspective for BD imaging alteration.

The Human Brainnetome Atlas was used to segment the insula into 12 subregions in 82 BD patients (43 finished follow-up) and 88 healthy controls (HCs). Whole-brain voxel-based FC analysis was performed to investigate the FC of the insular subregions in BD patients before and after three-month treatment. The insular subregion FC was then used to train support vector machine (SVM) models for patient identification.

At baseline, six insular subregions showed abnormal FC with the dorsolateral prefrontal cortex, orbitofrontal cortex, thalamus, and brain regions in the default mode network (DMN) and visual network (VN). The follow-up study found partially normalized FC between the insula and the superior frontal gyrus, further increased insular FC with the DMN and VN, as well as novel increased FC with the superior temporal gyrus. The SVM module exhibited 73.75% classification accuracy.

This study indicates that the insula subregions FC may serve as characteristic changes in BD patients and are sensitive to treatment.