Bipolar I disorder patients who are in remission display increased coupling between brain regions involved in regulating emotions, even in the absence of a psychological task, shows a US study.
The researchers found hyperconnectivity between the right ventrolateral prefrontal cortex (vlPFC) and the right amygdala in the patients. They report that the connectivity between these two regions was partly mediated by the anterior cingulate cortex (ACC).
"Together, these findings suggest a maladaptive misallocation of neural resources in bipolar disorder," they write in Bipolar Disorders. "Intrinsic hyperconnectivity in the bipolar I disorder group between regions, in the 'normal' euthymic state and while at rest, could be evidence of a trait marker of disease pathophysiology."
Salvatore Toreros (University of California, Los Angeles) and colleagues studied performed resting state functional magnetic resonance imaging of 20 euthymic bipolar I disorder patients and 20 mentally healthy controls.
After false discovery rate-multiple comparison correction, there was significantly increased connectivity between the right amygdala and the right vlPFC on region of interest (ROI) to ROI analysis in patients relative to controls. This was virtually unchanged by taking into account head movement measurements.
Whole-brain analysis confirmed the significant hyperconnectivity between the right amygdala and right vlPFC, and also revealed significant regional hyperactivity between other regions, such as the right and left medial frontal gyri, the right superior temporal gyrus, and the precentral gyrus. There were no whole-brain connectivity differences between bipolar patients and healthy individuals in primary somatosensory, auditory, or visual regions.
Among the patients, there was no significant correlation between right amygdala and right vlPFC connectivity and illness duration, number of depressions, number of manias, or Hamilton Depression Rating Scale and Young Mania Rating Scale scores.
Further analysis revealed that a significant cluster in the ACC was strongly and positively functionally connected to both the right amygdala and right vIPFC. A mediation model showed that the ACC partially mediated the influence of the vlPFC on the amygdala, and the mediation effect was significant on the Sobel test.
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