By Eleanor McDermid, Senior medwireNews Reporter
Some of the alterations in brain activation in patients with bipolar disorder are dependent on their current mood, study findings show.
Brain activation in bipolar patients during the n-back working memory task followed a similar general pattern to that seen in mentally healthy controls, report Edith Pomarol-Clotet (Barcelona and Centro de Investigación Biomédica en Red de Salud Mental, Spain) and study co-authors.
However, the areas of activation/deactivation were “noticeably less extensive” and the degree of activation or deactivation was less.
The 114 bipolar patients had significant failure of deactivation in the medial frontal cortex, relative to 38 mentally healthy controls who were matched for age, gender and IQ. This finding, implying default mode network dysfunction, “was seen in all three illness phases and so seems to represent a trait-like abnormality”, writes the team in The British Journal of Psychiatry.
Another trait-like finding was reduced activation in the dorsolateral prefrontal cortex. However, although activation was reduced in all bipolar patients relative to controls, the size of the reduction was largest among patients who were in a manic episode, suggesting that activation in this region is also state-dependent.
By contrast, activation in the dorsal parietal cortex was entirely mood-dependent, being significantly less in patients who were currently manic or currently depressed (both n=38), relative to activation in controls, but unaffected in patients who were currently euthymic (n=38).
The researchers say this latter finding is unexpected, given that altered activation in the dorsal parietal cortex was not found in recent meta-analyses. However, they note that the parietal cortex is part of the working memory network; few of the studies in these meta-analyses assessed patients during a working memory task, so the differences in parietal cortex activation would not be apparent.
“If this explanation is correct, it might be expected that a different pattern of mood-state dependent changes would be found if other tasks were used”, write Pomarol-Clotet et al.
They say that the differences found between euthymic patients and those in a mood episode “could have reflected either the obvious symptomatic differences between the two states, or alternatively improvement in cognitive function taking place with recovery.”
They consider the second explanation to be the most likely, because they used a cognitive, rather than an emotional, test, but caution that “the view that cognitive impairment in depression and mania normalises with clinical recovery is almost certainly an oversimplification.”
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