Study results show that amygdala activation during motor response inhibition decreases between mania and remission in patients with bipolar disorder (BD).

Arthur Kaladijan (Universite de la Mediterranee, Marselle, France) and co-authors say that the study findings “place emphasis on amygdala responsiveness as one critical determinant of mood regulation in BD,” and suggest that psychotropic medications should reduce amygdala responsiveness in order to treat manic symptoms effectively.

For the study, the researchers used a longitudinal design to examine the functional changes associated with symptomatic remission from mania the brain network underlying motor response inhibition.

In total, 10 BD patients and 10 healthy controls were imaged twice, first during a manic state and then during full remission, using event-related functional magnetic resonance imaging (MRI) while performing a Go/NoGo task.

The researchers found that the left amygdala was the only brain region that showed a time-dependent change in activation, which was significantly different between BD patients and healthy individuals.

Further analysis showed that BD patients had a lower activation while in full remission than in a manic state, whereas no difference was seen in between both time points in healthy individuals. Additionally, BD patients showed a reduced activation at the left amygdala during remission compared with healthy individuals.

“This indicates that a decrease of the left amygdala activation over time distinguishes the BD group from the [healthy control] group,” write the researchers in the journal Bipolar Disorders.

Kaladijan and team say that clear explanation cannot be provided for why the mood-related change in amygdala activation was observed in only the left hemisphere. They do note, however, that the left and right amygdale have been shown to play different roles in emotional processing.

“Thus, a brain dysregulation that involves the amygdala may lead to different clinical expression according to which side of this structure is affected,” comment the authors.

The researchers also say that the decrease in amygdala activation associated with remission is unlikely to reflect the direct effect of drug administration, since no changes in regimen occurred during the study.

“Further longitudinal studies comparing drug responders to nonresponders are needed to confirm this hypothesis,” they say.

MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a part of Springer Science+Business Media. © Current Medicine Group Ltd; 2009

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