The underlying neural mechanisms for processing affective stimuli appear to differ in patients with bipolar disorder II, compared with those of healthy controls, a study has shown.
Both functional MRI scans during patients’ exposure to facial expressions and an overt task of identifying fearful or happy faces revealed differences in bipolar patients’ processing of emotional information relative to healthy controls, reported Kelly A. Sagar and her associates at McLean Hospital, Belmont, Mass., in the Journal of Affective Disorders (2013 May 30 [doi:10.1016/j.jad.2013.05.019]).
Ms. Sagar’s team wrote that their findings suggest that bipolar I patients "have difficulties with the identification of certain emotional expressions," potentially resulting "in an inability to appropriately read social cues, which often leads to miscommunication, misinterpretation, and compromised interpersonal relationships."
The researchers assessed the affective processing of 23 bipolar I patients and 18 healthy controls in two separate tasks. The bipolar I patients, with a mean age of 26.65 (plus or minus 6.65) and a mean bipolar disorder onset age of 16.5 (plus or minus 3.65) were primarily euthymic at the time of the study, and their pharmacotherapeutic regimens had been stable for at least 12 weeks before the study began.
Four bipolar patients were unmedicated at the time of the study, four were taking antidepressants, four were taking benzodiazepines, 11 were taking antipsychotics, and 17 were taking mood stabilizers. The healthy controls tended to be younger, with a mean age of 23.11 (plus or minus 3.15), but the controls’ years of education (15.53 plus or minus 21.22 ) were similar to those of the bipolar participants (14.57 plus or minus 1.68).
During the functional MRI task, the participants completed a backward-masked affect paradigm in which they viewed black and white photographs of male and female faces with different expressions, shown for 30 milliseconds each. The two affective conditions were fearful and happy, alternated with neutral faces and with neutral masks shown between each face for 170 milliseconds.
Ms. Sagar’s team reported results for both single sample analyses and contrast analyses (subtracting one group map from the other for each face condition).
In the single sample analyses, the patients with bipolar disorder showed altered activation in the amygdala and increased activation in the anterior cingulate and dorsolateral prefrontal cortex during the fear condition, compared with the controls. The bipolar patients’ activation patterns in these three regions were more diffuse during the happy condition than in the controls.
In the contrast analyses, relative to controls, bipolar patients showed increased activation in the anterior cingulate cortex, bilateral amygdala, and dorsolateral prefrontal cortex during the fear condition and higher activation in the subgenual anterior cingulate, right dorsolateral prefrontal cortex, and left amygdala during the happy condition. The controls showed higher activation in the midcingulate and left dorsolateral prefrontal cortex during the happy condition, compared with the participants with bipolar disorder.
After the functional MRI scan, participants completed the computerized Facial Expression of Emotion Stimuli and Test, in which they had to identify the most closely represented emotion (anger, disgust, fear, happiness, sadness, or surprise) for 60 faces shown for 5 seconds each.
The bipolar participants identified fewer of the fearful faces, with an average 68.91% accuracy (standard deviation = 21.74), compared with 80% accuracy (SD = 14.14) among the controls. Identification of the happy faces, however, was comparable between the groups, with 97.39% accuracy (SD = 7.51) among the bipolar participants and 98.89% accuracy (SD = 3.23) among the controls.
The researchers noted that the functional MRI scan results revealed that the differences in emotional processing between bipolar patients and healthy controls occurred when the stimuli were shown "below the level of conscious awareness, suggesting a disruption early in the neural circuit responsible for affective processing." These findings, along with the greater difficulty bipolar patients had in identifying fearful faces during the overt task, corroborate similar findings in other studies, including a meta-analysis finding impairments among bipolar patients in recognizing facial emotions.
"Given the behavioral alterations and difficulty in inhibiting inappropriate responses often seen in patients with [bipolar disorder], these findings may have implications for reading cues in social situations, which may result in negative consequences," the authors wrote.
The study was limited by the moderate number of participants, the statistically significant but likely not biologically significant, age differences between the two groups, and the inability to be certain whether medication status could have affected the results.
The study was funded by the Jim and Pat Poitras Foundation and by a National Institute on Drug Abuse grant. The authors reported that they had no relevant financial disclosures.