The functional organization of the brain, studied in functional MRI (fMRI), reflects the intrinsic activity of the brain subjected or not to a cognitive task, and makes it possible to locate functionally connected regions that are more or less distant. This functional connectivity supports the idea that brain functions do not simply depend on specific brain regions (localization theory), but on the exchange and communication between these regions. Furthermore, we know that functional dysconnectivity of the amygdala, a heterogeneous set of nuclei whose specific connectivity could lead to positive or negative emotional valence, is at the heart of the pathophysiology of bipolar disorder. However, to date, no study has examined the connectivity of the amygdala's sub-nuclei.
In the present work, the researchers used resting-state fMRI to examine the connectivity of amygdala sub-nuclei in 127 patients with mood disorders, at different phases (manic or depressive), and in 131 healthy subjects. They were thus able to distinguish different functional connectivity profiles between patients with depressive symptoms and those with manic symptoms. In particular, they found that patients in the depressive phase showed reduced connectivity between the lateral nucleus of the right amygdala and the hippocampus (anterior and posterior), while patients in the (hypo)manic phase showed increased connectivity between the medial nucleus of the left amygdala and the ventral part of the nucleus accumbens (an important region of the reward circuit).
Taken together, these results provide a better understanding of some of the mechanisms underlying mood variations in bipolar disorder, and underscore the importance of considering amygdala sub-nuclei separately when studying functional connectivity profiles. Non-invasive neuromodulation techniques, such as neurofeedback, could target the brain circuits identified in this study and reduce mood fluctuations in bipolar patients. Research in this direction is currently underway at NeuroSpin.
Contact : Pauline Favre pauline@favre-univ.fr ou pauline.favre@cea.fr