Researchers have identified distinct trait- and state-related neural abnormalities during emotional response inhibition in patients with bipolar disorder.
"Because clinically significant impairments central to all phases of bipolar disorder relate to difficulties in controlling emotional responses, it is important to understand the neural mechanisms driving these emotional regulation abnormalities," they comment in Biological Psychiatry.
Amit Anand (Indiana University school of Medicine, Indianapolis, USA) and colleagues carried out functional magnetic resonance imaging on unmedicated patients with bipolar mania (n=30), bipolar depression (n=30), or bipolar euthymia (n=14), and 30 mentally healthy individuals while the participants completed an emotional and nonemotional go/no-go task.
For the go/no-go task, the participants had to press a button in response to go cues, while withholding their response to no-go cues. For measuring emotional responses, happy and sad faces were used as the cues, while letters were used for nonemotional, cognitive responses.
The results showed that bipolar euthymic patients had higher insula activity during no-go responses to happy faces and greater activity in left inferior frontal gyrus during no-go responses to sad faces compared with mentally healthy individuals, indicating trait effects of bipolar disorder separate from any active mood symptoms.
"Notably, these increases... were present while inhibiting emotional information but not while inhibiting cognitive stimuli, indicating that abnormal inhibitory neural processes in bipolar disorder are dependent on emotional content," the researchers comment.
State effects were also evident, with the bipolar depression and bipolar mania patients showing lower insula activity during no-go responses to happy faces, compared with bipolar euthymia patients; activity was lower in the bipolar patients with depression than in those with mania.
This finding is consistent with prior literature on biases in emotional processing in depression, say the researchers.
"Decreased insula activation for the BD [bipolar depression] group may drive impairments in recognizing or responding to positive facial cues," they explain.
The bipolar depression and mania patients also had a greater response during no-go responses to sad faces in areas of the brain related to emotion processing and regulation, including the putamen, insula, and lateral prefrontal cortex, with the effects similar in both groups.
But Anand and team found that bipolar mania patients also had higher activity in the insula and putamen during no-go responses to letters.
"This data may reflect the overall inhibitory deficits of manic patients, which increase brain activity in emotion generating regions even during nonemotional tasks," they suggest.
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