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State-Dependent Differences in Emotion Regulation Between Unmedicated Bipolar Disorder and Major Depressive Disorder.

IMPORTANCE
Major depressive disorder (MDD) and bipolar disorder (BD) are difficult to distinguish clinically during the depressed or remitted states. Both mood disorders are characterized by emotion regulation disturbances; however, little is known about emotion regulation differences between MDD and BD. Better insight into these differences would be helpful for differentiation based on disorder-specific underlying pathophysiological mechanisms. Previous studies comparing these disorders often allowed medication use, limiting generalizability and validity. Moreover, patients with MDD and BD were mostly compared during the depressed, but not the remitted, state, while state might potentially modulate differences between MDD and BD.


OBJECTIVE
To investigate positive and negative emotion regulation in medication-free patients with MDD and BD in 2 mood states: depressed or remitted.


DESIGN, SETTING, AND PARTICIPANTS
A cross-sectional study conducted from May 2009 to August 2013 comparing behavioral and functional magnetic resonance imaging emotion regulation data of 42 patients with MDD, 35 with BD, and 36 healthy control (HC) participants free of psychotropic medication recruited from several psychiatric institutions across the Netherlands.


INTERVENTION
A voluntary emotion regulation functional magnetic resonance imaging task using positive and negative pictures.


MAIN OUTCOMES AND MEASURES
Behavioral and functional magnetic resonance imaging blood oxygen level-dependent responses during emotion regulation.


RESULTS
In the remitted state, only patients with BD showed impaired emotion regulation (t = 3.39; P < .001; Cohen d = 0.70), irrespective of emotion type and associated with increased dorsolateral prefrontal cortex activity compared with those with MDD and healthy control participants (P = .008). In the depressed state, patients with MDD and BD differed with regard to happy vs sad emotion regulation (t = 4.19; P < .001; Cohen d = 1.66) associated with differences in rostral anterior cingulate activity (P < .001). Patients with MDD regulated sad and happy emotions poorly compared with those with BD and healthy control participants, while they demonstrated no rostral anterior cingulate difference between happy and sad emotion regulation. In contrast, patients with BD performed worse than those with MDD on sad emotion regulation but normal on happy emotion regulation, and they demonstrated significantly less rostral anterior cingulate activity while regulating happy compared with sad emotions.


CONCLUSIONS AND RELEVANCE
Medication-free patients with MDD vs BD appear to differ in brain activations during emotion regulation, both while depressed and in remission. These different neuropathophysiological mechanisms between MDD and BD may be useful for further development of additional diagnostic tools.