Association between abnormal theta oscillation-default mode network functional connectivity and internet addiction behavior in adolescent depression patients: a resting-state EEG study.

BACKGROUND: Major depressive disorder (MDD) and internet addiction (IA) are closely linked in adolescents, yet the neurobiological mechanisms underlying their relationship remain unclear. This study aimed to explore the role of abnormal functional connectivity (FC) between theta oscillation and the default mode network (DMN) in IA development among adolescent MDD patients. METHODS: A total of 183 drug-naive first-episode adolescent MDD patients and 93 healthy controls (HC) were enrolled. Clinical assessments were conducted using the HAMD-24, HAMA, and Young Internet Addiction Scale, with MDD patients divided into IA and MDD subgroups. Resting-state EEG data were collected for time-frequency analysis, brain electrical source reconstruction, and FC analysis, with statistical tests performed via SPSS 22.0. RESULTS: The IA group had higher scores in depression, anxiety, anhedonia, and IA severity than the MDD and HC groups. Theta band power spectral density (PSD) was lower in the IA group than in the MDD group, while both MDD groups exhibited higher theta PSD than HCs. IA was associated with abnormal intra-DMN connections; theta oscillation mediated the relationship between anhedonia and IA severity. HC subjects had stronger DMN FC across Delta, Theta, Alpha, and Gamma bands than MDD patients, and the MDD group showed stronger theta-band DMN FC than the IA group. CONCLUSIONS: Abnormal theta oscillation-DMN network correlates with IA in adolescent MDD patients, and the mediating role of theta oscillation provides a new perspective for understanding the neural mechanism of this comorbidity.