Resting-state functional magnetic resonance imaging in bipolar affective disorder. A systematized umbrella review

Bipolar affective disorder (BD) is a complex mental illness that presents diagnostic challenges due to its heterogeneous nature. As a result, identifying potential markers for the disorder is crucial for effective diagnosis and treatment. Resting-state functional magnetic resonance imaging (rs-fMRI) is a promising non-invasive technique that provides a window into the pathophysiological characteristics of psychiatric and neurological diseases in vivo. The amount of data accumulated in the scientific community regarding changes in spontaneous activity and functional connectivity of brain regions in BD necessitates a comprehensive synthesis to determine the spectrum of disorders. Accordingly, a systematic review of reviews was conducted to summarize the changes characteristic of patients with BD as measured by fMRI. Qualitative synthesis of results of nine systematic reviews and six meta-analyses has allowed the definition of changes in spontaneous activity and functional connectivity most characteristic for BD, confirming the unity of functional disturbances of this nosological unit. The findings of the review indicate that the manic state in BD is often associated with increased activity of the amygdala and decreased functional connectivity between the amygdala and frontal regions. Conversely, the depressive phase is characterized by abnormalities of functional connectivity within the default mode network, particularly in relation to the posterior cingulate cortex. Changes in functional connectivity during periods of euthymia may reflect residual manifestations of one of the exacerbation phases or may be associated with a history of a psychotic episode. Furthermore, a comparative analysis of possible methods of quantitative fMRI data synthesis has been conducted for the first time in Russia, which is a valuable contribution to the field.