P 24 Electrophysiological connectivity during oscillatory cycles of alpha activity and the BOLD-signal correlate in major depression

Abstract

Introduction Major depressive disorder (MDD) belongs to the leading causes of disability worldwide. From an electrophysiological point of view, EEG-alpha activity and alpha phase synchronization seem to be possible biomarkers with diagnostic and prognostic value. In parallel, functional magnetic resonance imaging (fMRI) studies suggest altered blood oxygen-level dependent (BOLD) signals in e.g. frontal and prefrontal brain areas ( Lemogne et al., 2012 ). However, the association between electrophysiological alterations and differences of fMRI activity in MDD remains vague. The goal of this study was to analyze the linkage between physiologically synchronized neuronal activity and hemodynamic changes as assessed by simultaneous EEG-fMRI recordings and its alterations in MDD. Method Therefore, simultaneous EEG-fMRI 12 min resting state measurements of 22 unmedicated MDD-patients and 15 healthy controls were conducted. EEG phase synchronization as markers for cortical connectivity between two scalp regions were calculated at the electrode level. Time series of the phase synchronization were averaged according to the repetition time (2400 ms) and used as regressors for the BOLD signal analysis. Results While interhemispheric activity e.g. between electrodes F3 and F4 showed increased BOLD signals in associated areas at both sides in healthy subjects, intrahemispheric connectivity, e.g. between C3 and O1 was associated with heterogeneous patterns with mainly frontal increased and occipitally decreased BOLD signals. Concerning the EEG phase synchronization associated BOLD signals, a significant difference between patients suffering from MDD and healthy subjects was found within the subgenual gyrus for a variety of intra- and interhemispheric EEG-connections. In particular, in patients, the subgenual gyrus seems to be more involved in the regulation of EEG-alpha synchronization in comparison to healthy controls. Conclusion EEG-alpha phase synchronization is associated with marked BOLD signal changes. The regulation of EEG-alpha phase synchronization seems to be altered in MDD with the subgenual gyrus as a key hub.