Abnormalcerebral-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 among 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

No significant group differences in cerebral-limbic functional connectivity survived false discovery rate (FDR) correction for multiple comparisons (p<0.05); thus, all reported abnormal FC patterns were identified at a stringent uncorrected statistical threshold of p<0.001 and should be strictly interpreted as exploratory neurofunctional trends without statistical validation at the individual connection level. 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 show distinct and divergent cerebral-limbic FC patterns: reduced DMN FC in BD-M and increased DMN FC in BD-D. These exploratory patterns suggest potential neurofunctional correlates of mood states in bipolar disorder, offering preliminary clues to state-related differences that require validation in larger independent cohorts.