Within- and Between-Session Changes in Neural Activity During Emotion Processing in Unipolar and Bipolar Depression

Abstract

BackgroundBipolar disorder (BD) and unipolar depression (UD) can be difficult to distinguish clinically, particularly during episodes of depression. In this study, we test for differences between adults with BD, adults with UD, and healthy control (HC) adults regarding within-session and between-session changes in blood oxygen level–dependent (BOLD) response during implicit emotional processing. MethodsDuring functional magnetic resonance imaging, HC adults (n = 19) and adults with UD (n = 19) and BD (n = 16) performed an implicit emotion processing task. Each participant was scanned twice, separated by 6 months, resulting in 108 scans. The BOLD response and linear change in BOLD response were examined within and between sessions. ResultsWe observed within-session linear decreases in BOLD signal (regardless of group, condition, or session) in the left amygdala, a right-sided temporoparietal region, and a right-sided frontoinsular region. We also observed group differences in within-session BOLD signal change (p < .05, familywise error corrected) in a left-sided striatoinsular-thalamic region. Adults with BD demonstrated a linear decrease in BOLD signal compared with HC adults (p < .008, familywise error corrected) across this region and compared with adults with UD in the posterior insula portion of the region (p < .008, familywise error corrected). Finally, we observed main effects of emotional valence in bilateral visuospatial processing regions as well as in the left and right amygdala. ConclusionsAdults with BD demonstrated linear attenuation of BOLD response to emotional stimuli within left-sided striatoinsular-thalamic regions. Adults with BD may either have experienced abnormal habituation in this region or have disengaged quickly from processing the emotional stimuli, despite comparable task performance. This pattern may represent an underlying pathophysiologic process associated with BD that differs from UD.