Brain functional networks and structures that categorize type 2 bipolar disorder and major depression.

Background: Distinguishing between type 2 bipolar disorder (BD II) and major depressive disorder (MDD) poses a significant clinical challenge due to their overlapping symptomatology. This study aimed to investigate neurobiological markers that differentiate BD II from MDD using multimodal neuroimaging techniques.

Methods: Fifty-nine individuals with BD II, 114 with MDD, and 117 healthy controls participated in the study, undergoing structural and functional magnetic resonance imaging. Functional connectivity (FC) analysis used regions from Shen's whole-brain FC-based atlas. Feature selection was carried out using independent t-tests and ReliefF algorithms, followed by classification using Support Vector Machine and wide neural network.

Results: Significant differences in brain structure and function were observed among patients with BD II, MDD, and healthy controls. Both structural and functional alterations were more pronounced in BD II compared to MDD, particularly in regions associated with sensory processing, motor function, and the cerebellum. Classification based on neurobiological markers achieved a mean testing accuracy of 88.24%, with the t-test selected features outperforming those selected by ReliefF. Dysconnectivity patterns correlated with symptom severity and functioning in BD II but not MDD.

Conclusion: Our findings suggest that neurobiological markers derived from multimodal imaging techniques can effectively differentiate patients with BD II from those with MDD. The identified alterations in brain structure and function, particularly in sensory-motor processing networks, may serve as potential biomarkers for distinguishing between these mood disorders. However, the influence of psychotropic medications and daily functioning severity on these neurobiological markers warrants further investigation.