The delta/alpha ratio in sleep EEG increases with the severity of depression in patients over 50 years old

The delta/alpha ratio (DAR) of sleep electroencephalography (EEG) frequency band parameters is closely related to cognitive control in healthy adults, but its role in patients with depression over the age of 50 remains unclear. Currently, a comprehensive and reliable indicator to distinguish the severity of depression in this population is still lacking.

This study included 88 participants, all of whom underwent overnight polysomnography. Among them, 30 were in the normal control group (Hamilton Depression Rating Scale (HAMD) ≤ 8), 22 in the mild-to-moderate depression group (HAMD ≤ 35), and 36 in the severe depression group (HAMD > 35). We compared demographic characteristics, polysomnographic features, relative EEG spectral power, and their ratios among the three groups.

The DAR value in the severe depression group was significantly higher than that in the mild-to-moderate depression group. Spearman correlation analysis indicated that the DAR value was positively correlated with depression scores. After adjusting for age, gender, BMI, alcohol, disease duration, and age of onset, logistic regression analysis demonstrated that both the DAR value during Non-Rapid Eye Movement (NREM) sleep (p = 0.017) and Rapid Eye Movement (REM) sleep (p = 0.029) were closely associated with depression. ROC curve analysis revealed that the area under the curve (AUC) for NREM-DAR in depression patients was 0.691, with a sensitivity of 65.7% and a specificity of 81.8%.

DAR values strongly correlate with depression severity, suggesting their potential use as a diagnostic marker. NREM-DAR may be a risk factor for severe depression, while REM-DAR may serve as a protective factor.