Decreased functional connectivity in the language regions in bipolar patients during depressive episodes but not remission

Abstract Background Retardation of thought is a crucial clinical feature in patients with bipolar depression, characterized by dysfunctional semantic processing and language communication. However, the underlying neuropathological mechanisms remain largely unknown. The objective of this study was to evaluate the disruption in resting-state functional connectivity in 90 different brain regions during the depressive episodes of bipolar disorder and during disease remission. Methods Applying the whole brain and language regions of interest methods to the resting-state functional magnetic resonance imaging data, we explored the discrepancies in 90 brain regions' functional connectivity in 42 patients with bipolar disorder — 23 experiencing a depressive episode and 19 in remission — and 28 healthy controls matched for gender, age, and education. Results Bipolar depressive patients had significantly reduced connectivity strength in the language regions relative to healthy controls. Specifically, the affected regions included the left triangular part of the inferior frontal gyrus, left opercular part of the inferior frontal gyrus, left middle temporal gyrus, and left angular gyrus. However, no significant differences in these regions were observed between bipolar patients in remission and healthy controls. Furthermore, the decreased connectivity strength between the left middle temporal gyrus and right lingual gyrus showed significant positive correlation with the scores on the Hamilton Depression Rating Scale. Limitations Bipolar depressive patients received treatment of benzodiazepines, which may confound the findings. Conclusions Our results illustrated that connectivity disturbances in the language regions may change depending on the disease phase of bipolar disorder.