Study findings suggest that patients in the depressive phase of bipolar disorder (BD) show dysfunction in prefrontal-limbic networks and associated striatal systems, which can be measured using amplitude of low-frequency fluctuations (ALFF).
According to Zhi Yang (Chinese Academy of Sciences, Beijing) and co-authors, the findings from this functional magnetic resonance imaging (fMRI) study support a model of BD involving dysfunction of prefrontal-limbic networks and associated striatal systems.
"These findings shed light on the pathophysiological mechanisms reflected in the resting state brain activity in BD and demonstrate the feasibility of using the ALFF as a research and clinical tool to monitor persistent cerebral dysfunction in bipolar depression," say the researchers in Psychiatry Research: Neuroimaging.
This study is the first application of ALFF to BD depression given that previous functional connectivity studies in BD may not be accurate because, according the authors, they cannot provide direct information about the overall regional differences in brain activity.
Comparison of fMRI scans from 26 patients with BD depression and 26 gender-, age-, and education-matched healthy controls revealed that patients with BD depression had significantly increased ALFF in the left insula, the right caudate nucleus, the temporal gyrus, the bilateral inferior frontal gyrus, and posterior lobe of the cerebellum.
These identified brain regions with increased ALFF are part of the prefrontal-limbic and striatal systems, which play important roles in affective processing, decision-making, and social cognition.
Decreased ALFF was observed in the left postcentral gyrus, the left parahippocampal gyrus, and cerebellum in patients with BD depression compared with healthy controls. "Consistent with previous reports, our findings in these regions may relate to impairments of emotional processing in BD," say the researchers.
Analysis of correlations between the ALFF and clinical data revealed a significant negative correlation between regional ALFF values in the left insula in BD patients and the Hamilton Depression Rating Scale (HDRS) score.
There were no other associations with clinical variables, which included patient age, years of education, number of depressive episodes, or disease duration.
Yang and team call for further verification of their study findings in a larger sample of unmedicated individuals, in addition to combining findings from existing functional connectivity studies to facilitate the understanding of the impaired prefrontal-limbic network.
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