Major depressive disorder is characterized by differential theta and alpha patterns during working memory updating

BACKGROUND: This study aimed to evaluate the working memory (WM) updating ability of patients with major depressive disorder (MDD) and investigate the potential underlying neuroelectric oscillatory mechanisms. The overall goal was to identify potential biological markers of impaired WM updating function in MDD. METHODS: 56 patients with MDD and 43 age- and gender-matched healthy controls (HCs) were recruited. All participants underwent clinical evaluations and electroencephalography (EEG) was used to record their brain activity in real time while performing the n-back task (0- and 2-back). Two-way analysis of variance was used to compare the WM behavioral performance and theta (4-8 Hz), alpha (8-13 Hz), and gamma (30-45 Hz) band powers between the two groups. Further, Spearman correlation analysis was performed to examine the relationships between the significant differential oscillation patterns and (1) emotional symptoms and (2) WM performance in the MDD group. RESULTS: Compared to the control group, the MDD group showed poorer accuracy and reaction time in the 2-back task. During the WM encoding phase of the 2-back task, the patient group exhibited decreased parietal theta oscillation activity, which was significantly correlated with lower accuracy and longer reaction times. Additionally, the control group exhibited stronger frontal-midline theta and occipital alpha oscillations during the 2-back task. This distinct pattern of activity as a function of task difficulty was not observed in the MDD group. CONCLUSIONS: MDD patients demonstrated impaired WM updating ability, primarily due to abnormalities in the memory encoding phase. The weakened parietal theta oscillation activity and the abnormal patterns of frontal-midline theta and occipital alpha oscillations might constitute the neurophysiological basis of these functional differences.