Ventral striatal activity possible biomarker for bipolar II disorder
medwireNews: Researchers have observed increased activity in the ventral striatum in response to reward anticipation in patients with bipolar II disorder compared with patients with bipolar I disorder and mentally healthy controls, leading them to suggest that it could be a biomarker for the disorder.
Results from the study, published in The American Journal of Psychiatry, also found that those with bipolar II disorder had significantly greater left putamen volumes than those with bipolar I disorder and that left putamen volume correlated with left ventral striatal activity in response to reward anticipation.
"Our findings are among the first to identify patterns of abnormal neural activity in bipolar II disorder that may be potential targets for therapeutic interventions for this disabling psychiatric disorder," comment lead researcher Xavier Caseras (Cardiff University, UK) and team.
Thirty-two euthymic patients with bipolar disorder, 15 of whom had a diagnosis of bipolar II disorder, were recruited for the study, along with 20 mentally healthy comparison individuals.
All participants were assessed with the Mini-International Neuropsychiatric Interview, the Hamilton Depression Rating Scale, the Young Mania Rating Scale, and a questionnaire assessing the strength of the behavioral activation and inhibition systems, which regulate responses to reward and punishment. They were then asked to perform a monetary reward-processing task while being imaged using functional magnetic resonance imaging (fMRI).
Region-of-interest analyses of the fMRI images revealed that there was significant activation of the ventral striatum in all participants during reward anticipation, but that this was significantly greater in patients with bipolar II disorder than for either of the other groups.
This ventral striatal activity was associated with participants' scores on the behavioral activation system fun-seeking scale across all individuals.
The researchers suggest that this could either be due to "greater sensitivity of reward neural circuitry activity than self-report measures in differentiating bipolar I and II patients or greater ventral striatal activity for a given level of self-reported fun and thrill seeking during reward anticipation in bipolar II patients than other groups."
However, despite the significant differences in ventral striatal activity, the groups did not differ on self-reported measures of reward sensitivity. Interestingly, bipolar I disorder sufferers showed significantly greater ventral striatal activity than bipolar II patients on receiving a positive outcome in the task, although this difference did not remain after controlling for the potential effects of antipsychotics.
Caseras and colleagues conclude: "Bipolar I and bipolar II patients may be distinguished by functional differences in ventral striatal activity during reward anticipation and outcome, which in turn may suggest different neural mechanisms predisposing to mood dysregulation across bipolar I and II disorders."
medwireNews (www.medwirenews.com) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2013
By Afsaneh Gray, medwireNews Reporter