The connectivity of 2 large-scale brain networks is significantly altered in the different mood states of bipolar disorder, according to research published in the Journal of Affective Disorders.1
The authors previously noted that mood state speciﬁc aberrant connectivity between the amygdala and brain regions implicated in emotion regulation even under rest (non-task) conditions.2 Additionally, research is increasingly showing links between altered neural activity and cognitive tasks including emotion and reward processing.
In the present study, researchers at Harvard Medical School compared the spontaneous brain activity of adult patients with bipolar disorder type I (per DSM-IV criteria) to the brain activity of healthy controls. The bipolar group consisted of 23 patients in a manic episode and 24 patients in a euthymic state, most of whom were currently or previously hospitalized at McLean Hospital, and the control group consisted of 23 individuals. Functional connectivity between the brain regions of each participant was measured with resting state functional magnetic resonance imaging (rsfMRI) scans.
Consistent with the authors’ expectations, there were significant state-related functional alterations in both the dorsal attention network (DAN) and the default mode network (DMN), and these changes also differentiated the 2 bipolar states from the brain activity of the control group. In the DAN, there was greater connectivity between parietal, occipital, and frontal nodes during mania compared to both euthymic and healthy participants. This network is believed to influence the distribution of cognitive resources in pursuit of goals or external stimuli.
In the DMN, study participants who were in the euthymic state demonstrated hypoconnectivity between the dorsal frontal lobes and the rest of the DMN, while study participants in the manic state showed connectivity similar to healthy controls. These findings are consistent with the authors’ earlier findings of healthy controls’ amygdala activity falling roughly between that of bipolar mania and euthymia, and “we conjectured that the difference between HC and bipolar euthymia may represent a compensatory mechanism rather than a disease process,” they wrote.
The observed state-related alterations in DAN and DMN connectivity “suggest a circuit based pathology underlying cognitive dysfunction as well as activity/reactivity in bipolar mania,” the authors of the study noted. “Altered activities in neural networks may be biomarkers of bipolar disorder diagnosis and mood state that are accessible to neuromodulation and are promising novel targets for scientific investigation and possible clinical intervention.” One line of future research in this area will be examining whether DAN connectivity predicts behavioral performance and emotional reactivity, according to the researchers.
- Brady RO Jr, Tandon N, Masters GA, et al. Differential brain network activity across mood states in bipolar disorder. J Affect Disord. 2016; 207:367-376.
- Brady RO Jr, Masters GA, Mathew IT, et al. State dependent cortico-amygdala circuit dysfunction in bipolar disorder. J Affect Disord. 2016; 201:79-87.