Loss of superiority illusion in bipolar depressive disorder: A combined functional and structural MRI study

Superiority illusion (SI) is a positive cognitive bias related to self, manifested as overestimated self-appraisal. Negative self-schema is a core feature of the cognitive model of depression, including bipolar depressive disorder (BDD). However, only little research has explored the impaired self-processing in BDD. The potential alteration of positive self-bias and the corresponding neural mechanism in BDD remains unclear. This study aimed to investigate the underlying neural mechanism of self-processing in BDD combining task-related functional magnetic resonance imaging and high-resolution T1 structural imaging. Forty-three BDD and forty-eight healthy controls were recruited and underwent a self-related task, where participants were required to evaluate how they compared with their average peers on a serial of positive and negative traits. We defined the ratio of neural activation and gray matter volume (GMV) in a region as the functional-structural coupling index to detect the changes of brain image in BDD. Furthermore, we used moderation analysis to explore the relationship among functional-structural coupling, behavioral scores and depression symptoms. BDD exhibited decreased task activation, GMV, and functional-structural coupling in bilateral anterior insula (AI) and inferior parietal lobule (IPL). The associations between functional-structural coupling in the right AI, IPL and negative trait self-rating scores were moderated by depressive symptom severity. The study revealed disturbed self-related processing and provided new evidences to neuropsychological dysfunction in BDD.