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

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