Power Spectral Slope as a Novel Brain Functional Marker for Major Depressive Disorder

Resting-state functional magnetic resonance imaging (rs-fMRI) is a powerful tool to reveal disrupted brain activity in major depressive disorder (MDD), but most studies have focused solely on low-frequency functional fluctuations, ignoring the fact that brain activity is composed of both low-frequency and high-frequency fluctuations. Therefore, we applied a novel approach, namely the power spectral slope (PSS), which captures the characteristics of both low- and high-frequency fluctuations to evaluate brain activity in MDD.

rs-fMRI data were collected from 109 patients with MDD (27.29 ± 7.11 years, 75 women) and 78 normal control participants (26.47 ± 6.19 years, 51 women). A subset of 52 patients with MDD also underwent rs-fMRI scanning after a 12-week antidepressant treatment (escitalopram/duloxetine). Both the baseline between-group comparison and follow-up within-group comparison were performed for PSS. A 2-sample t test was used for baseline comparison with a liberal Gaussian random-field correction. The follow-up comparison was tested with paired t test.

Patients with MDD showed significantly more negative PSS compared with normal control participants in the ventral striatum and temporal pole. After treatment, PSS in the ventral striatum increased significantly toward normalization, whereas the temporal pole's slope remained unchanged. No significant correlations were found between PSS and depression severity scores.

This study demonstrates that MDD is characterized by more negative PSS in key affective regions. The normalization effect of ventral striatum spectral slope following antidepressant treatment suggests a region-specific response. Taken together, the findings suggest that PSS may serve as a novel brain functional marker for MDD.