Brain Abnormalities During Self-Referential Task in Subthreshold Depression: A Near-Infrared Spectroscopy Study

Background and aim Subthreshold depression is a potential risk factor for major depressive disorder. Although the neurobiological mechanism underlying major depressive disorder is well-established, the mechanism underlying subthreshold depression has not yet been fully elucidated. We investigated the characteristics of brain abnormalities in participants with subthreshold depression using near-infrared spectroscopy (NIRS) owing to its portability. Methods A total of 53 college students were recruited, and all participants performed three tasks: self-referential task (SRT), verbal fluency task (VFT), and category fluency task (CFT). Hemodynamic changes in the prefrontal cortex (PFC) during the tasks were also measured using NIRS. A generalized linear model was employed for the NIRS data analysis. Subsequently, we evaluated the relationship between depressive severity and NIRS data during task performance. Results Our analysis revealed a positive correlation between hemodynamic changes in the right PFC during the SRT and depression severity (SRTL_coeff: 0.12), suggesting that increased activation in this region may be associated with higher levels of depressive severity. In contrast, hemodynamic changes in the left PFC during the SRT did not significantly influence the severity of depression. Additionally, hemodynamic changes during the VFT and CFT did not significantly influence the severity of depression. Conclusions Hyperactivation of the right PFC, which is a characteristic of subthreshold depression, may cause a negative bias, leading to high sensitivity to negative stimuli. These results provide novel insights into the neural mechanism of subthreshold depression and highlight the utility of NIRS for evaluating brain function related to negative bias in the right PFC.