Functional MRI Differences in Emotional Regulation Pathways Associated with Unmedicated Bipolar II Disorder Depression
Marusak, Hilary A.
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Bipolar Disorder (BP) is a psychiatric illness characterized by episodes of abnormally elevated mood, or mania. The literature on the BP II variant is limited and treatment and diagnostic strategies would be more effective if the underlying neurobiology was better understood. There are several subcortical networks responsible for modulating emotion, and previous studies suggest that abnormalities in function are responsible for, or indicators of the types of mood aberrations observed in BP. These networks can be studied using functional magnetic resonance imaging (fMRI) techniques, which measure blood oxygenation level dependent (BOLD) responses to activity over time. Similar fMRI studies have utilized an event-related face-matching paradigm to activate this network and those on BP I depression are indicative of decreased activation in the amygdala as well as the bilateral orbitofrontal cortex, specifically Brodmann Area 47 (BA 47). This is contrasted to a reported increase in activation of the amygdala with the same BA 47 attenuation in the manic state. Using the same paradigm, this study is the first to examine the depressive phase of a medication-naïve BP II patient population in comparison to healthy controls. BP II depressed subjects demonstrated attenuation in both the right-sided amygdalar response as well as right BA 47, suggesting the possibility of a state-related amygdalar response or vulnerability to mood, which is apparent in the varying nature of both poles of the disorder. The role of BA 47 as a trait marker for the disorder is an area for further investigation, as it seems to function independently of mood state. Understanding the structural and functional, as well as state versus trait related variations hold important clinical and therapeutic implications for the normal brain, those with BP, and other psychiatric disturbances.