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Relatively few studies have investigated whether relatives of patients with bipolar disorder show brain functional changes, and these have focused on activation changes. Failure of de-activation during cognitive task performance is also seen in the disorder and may have trait-like characteristics since it has been found in euthymia.
A total of 20 euthymic patients with bipolar disorder, 20 of their unaffected siblings and 40 healthy controls underwent functional magnetic resonance imaging during performance of the n-back working memory task. An analysis of variance (ANOVA) was fitted to individual whole-brain maps from each set of patient–relative–matched pair of controls. Clusters of significant difference among the groups were used as regions of interest to compare mean activations/de-activations between them.
A single cluster of significant difference among the three groups was found in the whole-brain ANOVA. This was located in the medial prefrontal cortex, a region of task-related de-activation in the healthy controls. Both the patients and their siblings showed significantly reduced de-activation compared with the healthy controls in this region, but the failure was less marked in the relatives.
Failure to de-activate the medial prefrontal cortex in both euthymic bipolar patients and their unaffected siblings adds to evidence for default mode network dysfunction in the disorder, and suggests that it may act as a trait marker.
The subgenual anterior cingulate cortex (sgACC) is considered to be an important site of abnormality in major depressive disorder. However, structural alterations in this region have not been a consistent finding and functional imaging studies have also implicated additional areas.
A total of 32 patients with major depressive disorder, currently depressed, and 64 controls underwent structural imaging with MRI. Also, 26 patients and 52 controls were examined using functional magnetic resonance imaging (fMRI) during performance of the n-back working memory task. Structural and functional changes were evaluated using whole-brain, voxel-based methods.
The depressed patients showed volume reductions in the sgACC and orbitofrontal cortex bilaterally, plus in both temporal poles and the hippocampus/parahippocampal gyrus on the left. Functional imaging revealed task-related hypoactivation in the left lateral prefrontal cortex and other regions, as well as failure of deactivation in a subcallosal medial frontal cortical area which included the sgACC.
Whole-brain, voxel-based analysis finds evidence of both structural and functional abnormality in the sgACC in major depressive disorder. The fact that the functional changes in this area took the form of failure of deactivation adds to previous findings of default mode network dysfunction in the disorder.
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