Functional connectivity in major depression: Increased phase synchronization between frontal cortical EEG-source estimates

Structural and metabolic alterations in prefrontal brain areas including the subgenual (SGPFC), medial (MPFC) and dorsolateral prefrontal cortex (DLPFC) have been shown in major depressive disorder (MDD). Still it remains largely unknown how brain connectivity within these regions is altered at the level of neuronal oscillations. Therefore the goal was to analyze prefrontal electroencephalogram (EEG) phase synchrony in MDD and its changes after antidepressant treatment.

In 60 unmedicated patients and 60 healthy controls (HC) a 15 minute resting EEG was recorded at baseline and in a subgroup after two weeks of antidepressant medication. Symptom severity was assessed using the Hamilton Depression Rating Scale (HDRS). EEG functional connectivity between the SGPFC and the MPFC and DLPFC was was calculated with eLORETA (Low Resolution Brain Electromagnetic Tomography) by means of lagged phase synchrony.

Patients revealed an increased prefrontal connectivity at the alpha frequency between the SGPFC and the left DLPFC/MPFC. A positive correlation was found for beta connectivity and change in HDRS scores. After treatment, an increased connectivity between the SGPFC and the right DLPFC at the beta frequency was found for MDD but not for HC.

MDD is characterized by increased EEG functional connectivity within frontal brain areas. These disturbances of neuronal communication are assessable via EEG and might have potential value as biomarkers.