Background: Major Depressive Disorder (MDD) and Bipolar Disorder (BD) can be difficult to differentiate, as both feature depressive episodes. Here we have utilized fMRI and a measure of trait bipolarity to examine resting-state functional connectivity of brain activation in the default mode network in youth with MDD and BD to isolate trait-specific patterns.
Methods: We collected resting-state fMRI scans from thirty youth (15 MDD; 15 BD, Type 1). The Bipolarity Index (BI) was completed by each patient's treating psychiatrist. Independent components analysis was used to extract a default mode network component from each participant, and then multiple regression was used to identify correlations between bipolarity and network activation.
Results: Activation in putamen/claustrum/insula correlated positively with BI; activation in the postcentral gyrus/posterior cingulate gyrus correlated negatively with BI. These correlations did not appear to be driven by movement in the scanner, state depression, gender or lithium use.
Limitations: There were group differences in state depression and sex that needed to be statistically covaried; differences in medication use existed between the groups; sample size was not large.
Conclusions: The identification of the putamen/claustrum in our positive correlation may indicate a potential trait marker for the psychomotor activation unique to bipolar mania. The negative correlation in the postcentral gyrus/posterior cingulate suggests that this functional inactivation is more specific to MDD and is consistent with previous research. Ultimately, this approach may help to develop techniques to minimize the current clinical dilemma by facilitating the classification between BD and MDD.
Keywords: Bipolar Disorder; Bipolar spectrum; Default mode network; Functional brain imaging; Major Depressive Disorder; Youth mental health.
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