Brain network communication in remission: a comparative study of bipolar and unipolar depression

Distinguishing between unipolar depression (UD) and bipolar disorder (BD) during periods of remission presents a significant clinical challenge. To mitigate the potential confounding effects of depressive episodes, our study compares the white matter networks of individuals with UD and BD in remission, aiming to explore the differentiation between these two affective disorders. Our cohort included 69 individuals with remitted UD, 55 with remitted BD, and 78 healthy controls (HC). We employed diffusion tensor imaging (DTI) to assess the white matter (WM) network. Additionally, we utilized a comprehensive set of connectome and five communication models to characterize the alterations within the whole-brain WM network. Compared to HC, both UD and BD patients showed reduced connectivity in the frontal orbital region, with BD patients exhibiting a more pronounced decrease. BD patients demonstrated superior navigation ability and higher shortest path metric values in key brain region connections compared to UD. Conversely, UD patients showed greater diffusion efficiency in certain brain regions. Communicability and search information analyses revealed distinct patterns of connectivity between the two patient groups, with potential implications for emotion regulation and information processing. Our findings highlight distinct brain connectivity patterns in BD and UD during remission, suggesting that these patterns could serve as neuroimaging biomarkers for differentiating between the two disorders. The study provides insights into the enduring effects of mood disorders on brain connectivity and has potential clinical implications for diagnosis and treatment.