Group-specific associations among sleep quality, depressive symptoms, and frontal alpha asymmetry in college students: evidence from a cross-sectional EEG study

Background Poor sleep quality is associated with depressive symptoms, but its accompanying neurophysiological correlates remain unclear in non-clinical college students. This study examined associations among sleep quality, depressive symptoms, and frontal alpha asymmetry (FAA) in students with and without elevated depressive symptoms. Methods This cross-sectional study included 120 college students, comprising 60 students with depressive symptoms (DS) and 60 non-depressed controls (NC), classified using the Self-Rating Depression Scale. Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI), and FAA was derived from resting-state EEG. Analyses included BMI-adjusted group comparisons, partial correlations, regression models, and an exploratory indirect-path analysis. False discovery rate correction was applied to multiple comparisons. Results After BMI adjustment, the DS group had higher PSQI scores [median (P25, P75): 7 (6, 10) vs. 3 (1, 5)] and lower composite FAA values [−0.041 (−0.116, 0.031) vs. 0.056 (0.017, 0.103); both p < 0.001] than the NC group. Similar FAA differences were observed using frontopolar and frontal electrode-pair indices. PSQI scores were positively correlated with depressive symptoms in both groups (DS: r = 0.412, q = 0.006; NC: r = 0.462, q = 0.001). In the DS group, composite FAA was negatively correlated with PSQI ( r = −0.322, q = 0.034) and depressive symptoms ( r = −0.388, q = 0.010); neither FAA-related association reached statistical significance in the NC group. After BMI adjustment, PSQI and FAA were jointly associated with depressive symptom severity in the DS group ( R 2 = 0.243). An exploratory indirect-path analysis yielded an indirect association estimate of 0.092 (95% bootstrap CI: 0.002–0.202). Conclusion Poorer sleep quality was associated with greater depressive symptom severity in both groups, whereas FAA-related associations were observed mainly in the DS group. These findings suggest that FAA may be a candidate neurophysiological correlate of the concurrent association between sleep quality and depressive symptoms in non-clinical college students. Causal mediation cannot be inferred from this cross-sectional study.