Aberrant Thalamic Functional Connectivity for the Differential diagnosis of Bipolar Disorder and Major Depressive Disorder

Bipolar disorder (BD) is regularly misdiagnosed as major depressive disorder (MDD). BD and MDD are characterized by a wide range of symptoms, cognitive impairments, and altered functional connectivity (FC) between different brain regions. The thalamus is the largest subcortical structure that relays motor and sensory signals to the cerebral cortex, which is crucial for perceptual awareness and cognitive process. Thalamic dysfunction has been associated with MDD, whereas fewer studies discussed the thalamic FC in BD. It remains unclear whether these distinct thalamic FC patterns are diagnosis-specific between both BD and MDD. Therefore, the aim of this study is to determine the distinct thalamic dysconnectivity features among depressed BD and MDD patients. We included 61 MDD patients, 40 BD patients and 63 healthy controls (HCs) who underwent resting-state functional magnetic resonance imaging (rs-fMRI) scanning. FC between the left and right thalamus was calculated and compared among the three groups, and one-way ANOVA followed by post-hoc t-tests were deployed. Compared with HCs, MDD patients showed an increased FC in the right superior parietal gyrus and left superior parietal gyrus within right thalamus and an increased FC in the left of middle temporal gyrus within the left of thalamus. BD patients likewise showed decreased FC in the right angular gyrus compared with HCs within the right thalamus. When Compared with BD patients, MDD patients showed an increased FC in the right superior parietal gyrus and left superior parietal gyrus with right thalamus and an increased FC in the left of middle temporal gyrus within the left part of the thalamus. Therefore, BD and MDD patients showed distinct patterns of abnormal thalamus- parietal gyrus FC, and thalamus- temporal gyrus FC. These distinct abnormal left and right thalamic FC patterns plays the role of a neurobiological feature and potential biomarker differentiating the depressive patient groups.