State-related functional specialization of visual regions in bipolar disorder across different mood states

Brain specialization is essential for human cognition and behavior, with abnormal specialization patterns reported in numerous psychiatric disorders. However, the specialization patterns in bipolar disorder (BD) across different mood states are poorly understood. We hypothesized that bipolar depression (BD-D) and mania (BD-M) would exhibit both shared and distinct abnormalities in brain specialization, which might normalize during the euthymia state (BD-E).

Whole-brain autonomy index maps of patients with BD (n = 93) and HCs (n = 87) were calculated based on resting-state functional MRI. Initially, we conducted analyses of covariance (ANCOVA) to compare the differences in autonomy index among BD-D (n = 32), BD-M (n = 26), and HCs. The differences in autonomy index between BD-E (n = 35) and HCs were further analyzed using two-sample t-tests. Searchlight multivariate pattern analysis (MVPA) was employed to differentiate among patient groups. Additionally, we conducted spatial correlation analyses between autonomy index and genetic as well as neurotransmitter profiles.

Significant differences were found in the right lingual/calcarine gyrus across BD-D, BD-M, and HCs. Post-hoc tests revealed increased autonomy index in the right calcarine/lingual gyrus in BD-D but not in BD-M compared to HCs. No significant changes were observed in BD-E relative to HCs. The right fusiform gyrus showed the highest classification accuracy (62.06 %) among the three BD groups, surviving false discovery rate correction. No spatial correlations were observed.

Increased specialization in the visual regions might represent state-related alterations in BD. These abnormal specialization patterns were normalized in BD-E, suggesting clinical remission.