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

Area of Science:

• Neuroimaging
• Psychiatry
• Cognitive Neuroscience

Background:

• Distinguishing between bipolar disorder (BD) and unipolar depression (UD) is clinically challenging, especially during depressive episodes.
• Functional magnetic resonance imaging (fMRI) can reveal differences in brain activity between these mood disorders.
• Previous research has not fully elucidated the neural underpinnings of emotional processing differences in BD versus UD.

Purpose of the Study:

• To investigate differences in blood-oxygen-level-dependent (BOLD) responses during implicit emotional processing between adults with BD, UD, and healthy controls (HC).
• To examine within- and between-session changes in BOLD signals to identify distinct neural patterns associated with each group.

Main Methods:

• fMRI scans were conducted on adults with BD (N=16), UD (N=19), and HC (N=19) performing an implicit emotion-processing task.
• Each participant underwent two scanning sessions separated by 6 months, totaling 108 scans.
• Analysis focused on within- and between-session BOLD signal changes, including linear trends.

Main Results:

• Linear decreases in BOLD signal were observed across all groups in the left amygdala, right temporo-parietal, and right fronto-insular regions.
• Significant group differences in within-session BOLD signal change were found in a left striatal-insular-thalamic region (p<0.05, FWE corrected).
• Individuals with BD showed a linear decrease in BOLD signal in this region compared to HC and UD, particularly in the posterior insula (p<0.008, FWE corrected).

Conclusions:

• Individuals with BD exhibited attenuated BOLD responses to emotional stimuli in left striatal-insular-thalamic regions.
• This pattern suggests potential abnormal habituation or rapid disengagement from emotional stimuli processing in BD, differentiating it from UD.
• These findings may reflect unique pathophysiological mechanisms underlying bipolar disorder.