MedWire News: Results from a brain imaging study suggest that amygdala dysfunction may be a state-related abnormality in bipolar disorder (BD) patients, whereas ventrolateral prefrontal cortex (vlPFC) dysfunction may be a trait-related abnormality.

Writing in the journal NeuroImage, Lori Altshuler (University of California Los Angeles School of Medicine, USA) and colleagues observe that "hyperactivity in the amygdala and hypoactivity in the vlPFC have been reported in manic bipolar patients scanned during the performance of an affective faces task."

However, they add: "Whether this pattern of dysfunction persists during euthymia is unclear."

To investigate further, the team studied 24 euthymic BD patients and 26 mentally healthy individuals who were matched for age, gender, educational level, and race.

All of the participants underwent functional magnetic resonance imaging of the brain while performing a task involving the matching and labelling of emotional facial expressions during various conditions.

Specifically, the amygdala activating, or "match emotion," condition required participants to choose one of two emotional faces at the bottom of a screen that best matched the emotional expression of a face at the top of the screen. The vlPFC activating, or "label emotion," condition required participants to choose one of two words at the bottom of the screen that best describes the expression of the emotional face at the top of the screen.

The researchers found that there were no significant differences between BD patients and controls regarding response times or accuracy of responses during performance of the two conditions.

There were also no significant between-group differences regarding amygdala activation during the tasks.

However, compared with controls, BD patients showed significantly reduced activation of the right vlPFC (Brodmann area 47) during the "label emotion" condition, as well as significantly reduced activation in right insula, putamen, thalamus, and lingual gyrus during this condition.

"Taken in context with prior studies of bipolar mania and euthymia, our findings support the possibility that amygdala dysfunction may represent a state-marker of bipolar illness, whereas vlPFC dysfunction may be independent of mood state and represent a trait-marker of the illness," conclude Altshuler and team.

They add: "Understanding these state- versus trait-related differences is of profound significance, both in terms of understanding the neuropathophysiology of the changing mood-states in bipolar illness, as well as understanding the stable, enduring (mood independent) abnormalities.

"Future studies, therefore, that assess the impact of mood state on activation in longitudinal samples are needed."

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