Decreased phase synchronization of the EEG in patients with major depressive disorder

The aim of this study is to investigate if patients with major depressive disorder exhibit deficits in information transmission among different cortical regions in a resting condition. Spontaneous EEG recordings were collected from 16 scalp sites of 12 major depressive patients (M: F = 5: 7) and age-matched 16 healthy subjects (M: F = 9: 7) in a resting condition. Synchronization likelihood measures were estimated as a measure of functional connectivity between all pairs of the EEG in major depressive patients and healthy subjects from different frequency bands (alpha, beta delta, theta, and gamma). The conventional coherence measures of the EEG were also estimated in both groups in order to compare with synchronization likelihood measures. We found that major depressive patients had a significant (P < 0.05) decrease in the mean synchronization likelihood compared with that of healthy subjects for delta (0.5 ~ 4 Hz) band and the F7, F3, Fp2, F4 and T3 for alpha (8 ~ 13 Hz) band, which cannot be detected by conventional coherence measures. This result indicates that major depressive patients exhibit significant deficits in information transmission among cortical regions in resting conditions, and that these deficits can be estimated by the synchronization likelihood measure of the EEGs recorded from cerebral cortex.