Abnormal cerebral-limbic functional connectivity between bipolar mania and bipolar depression under resting state

Objective Previous research has identified aberrant functional connectivity (FC) in the neural circuits of patients with bipolar mania (BD-M) and bipolar depression (BD-D), yet the specificity of these FC patterns to each mood state remains unelucidated. This study was designed to compare the cerebral-limbic FC characteristics of BD-M, BD-D patients and healthy control (HC) subjects. Method Resting-state functional magnetic resonance imaging (fMRI) was performed on 30 BD-M patients, 31 BD-D patients and 30 HC subjects. Interregional cerebral FC values were calculated for group-wise comparisons, and the correlation between abnormal FC and depressive symptom severity was further explored. Results Abnormal cerebral-limbic FC in the default mode network (DMN), attention network and limbic areas was observed in both BD-M and BD-D groups. Specifically, BD-D patients showed elevated FC mainly in the DMN [posterior cingulate gyrus (PCG), precuneus (PCUN)], attention network [superior parietal gyrus (SPG), inferior parietal gyrus (IPG)] and limbic regions [hippocampus (HIP), parahippocampus (PHG)], while BD-M patients displayed reduced cerebral-limbic FC in the DMN and limbic areas. Conclusions BD-M and BD-D patients exhibit characteristic and divergent cerebral-limbic FC abnormalities—DMN FC reduction in BD-M and FC elevation in BD-D. These specific FC patterns may act as potential resting-state biomarkers for distinguishing between the two mood episodes of bipolar disorder.