Abnormal emotional cue responses inherent in bipolar disorder
MedWire News: Exaggerated response to emotional signals in cortico-limbic brain regions may represent heritable functional abnormalities underlying the development of bipolar disorder, neuroimaging study findings indicate.
Functional neuroimaging studies have shown overactivity in the anterior limbic structures of the brain in patients with bipolar disorder in response to fearful and happy facial expressions.
But "it is unclear whether such abnormalities are associated with the illness state, or represent stable or heritable traits," note Simon Surguladze, from King's College London, UK, and colleagues.
To investigate, they carried out functional magnetic resonance imaging experiments of facial emotion processing in 20 patients with bipolar I disorder, 20 of their unaffected first degree relatives, and 20 mentally healthy volunteers.
In one experiment, the participants watched faces expressing fear of varying intensities (moderate and high) intermixed with non-emotional faces, and in the second experiment, they watched faces expressing moderate or high degrees of happiness intermixed with non-emotional faces.
The brain data were then entered into 2 (fear and happy) x 3 (neutral, moderate, and high) x 3 (patients, relatives, and controls) repeated measures ANOVA.
This showed that brain activity differed significantly among the groups in two main areas: the prefrontal cortex and the left putamen.
Activity in the medial prefrontal cortex was greater in patients and relatives, compared with controls, in response to moderate and intensive expressions of either fear or happiness. There was no difference in their response to neutral faces.
Moreover, the group differences were paralleled by a familiality effect, whereby a significant proportion of activation in the medial prefrontal cortex was accounted for by the activation in individuals belonging to the same families.
Activity in the putamen was greater in patients and relatives in response to moderate fear, compared with controls, while patients, but not relatives, also showed greater activity than controls in response to high intensity happy faces.
Thus, "relatives did not demonstrate as universally hyperactive a striatum as bipolar patients," say Surguladze and team in the journal NeuroImage.
The study findings also confirmed increased amygdala activity in patients and relatives, compared with controls, in response to intensively happy faces.
"Our study indicates that overactivation of medial prefrontal cortex and subcortical structures in response to facial emotion processing tasks may represent a neurobiological abnormality associated with genotypic variation conferring susceptibility for bipolar disorder, and provides a possible neurobiological substrate for further studies combining genetics and neuroimaging in the search for the effects of such genotypic variation," the team concludes.
MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010
By Lucy Piper