MedWire News: Patients with bipolar disorders show reduced corticostriatal responses to happy and neutral stimuli relative to mentally healthy individuals, results of a functional magnetic resonance imaging (fMRI) study demonstrate.
The effect persisted throughout elevated, depressed, and euthymic mood states, suggesting that it is a trait feature of the disorder, according to Hilary Blumberg (Yale School of Medicine, New Haven, Connecticut, USA) and colleagues.
A convergent body of evidence supports various brain abnormalities in emotional processing in bipolar disorder and suggests that some abnormalities are mood state dependent and others persist into euthymia.
However, few studies have assessed elevated, depressed, and euthymic mood states while individuals process emotional stimuli of varying valence to investigate trait- and state-related neural system responses.
In the current study, regional brain responses to positive, negative, and neutral emotional stimuli were assessed with fMRI in 76 individuals with bipolar disorders during elevated, depressed, and euthymic mood states and compared with responses in 58 mentally healthy controls.
During fMRI scans, participants performed a emotion recognition task in which they were asked to view happy, fearful, and neutral facial expressions.
Each face stimulus was displayed for 2 seconds and the participants were instructed to make a determination of whether the face was female or male.
Blumberg and colleagues found that patients with bipolar disorder displayed diminished activation in the ventral anterior cingulate cortex, orbitofrontal cortex (OFC), and ventral striatum during their responses to happy and neutral faces compared with the control group - irrespective of mood state.
By contrast, elevated mood states were specifically associated with decreased right rostral prefrontal cortex activation to fearful and neutral faces, and depression was associated with increased left OFC activation to fearful faces.
The results clearly support trait- and state-related functional abnormalities during emotional processing in bipolar disorder, say Blumberg et al in Bipolar Disorders.
The trait-related abnormalities suggest that positive - and perhaps emotionally ambiguous - stimuli elicit trait dysfunction.
Meanwhile, the acute mood states may be distinguished by additional abnormalities, including decreases in right rostral PFC responses to negative and ambiguous emotional stimuli in association with elevated mood state, and increases in left OFC responses to negative emotional stimuli in association with depressive states.
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