EEG Microstates in Major Depressive Disorder: Evidence Against Trait Markers of Illness

Abstract Dysconnectivity between cortical networks is a core feature of major depressive disorder (MDD). Electroencephalography (EEG) derived microstates are a cost effective and time sensitive method of examining the dynamics of large-scale brain networks. Previous studies examining the four traditional microstate classes of A, B, C, and D in MDD have used mixed diagnostic samples and have displayed varied results. More recently, there have been reports of altered microstate parameters in studies where five microstate classes best fit the data. To continue the examination of this phenomenon, the current study examined five microstate classes in individuals with MDD compared to healthy controls. Although a five-microstate model best fit our data, we failed to replicate any alterations in the duration, occurrence, contribution, or transitional probabilities of any microstate class in MDD. However, the number of observed transitions varied significantly from what would be expected between microstates A, B, and E in the MDD group, suggesting abnormal connectivity between regions responsible for generating these states. There was also a significant relationship found between anxiety symptoms and the occurrence of microstate class E in our MDD sample. Potential explanations for our findings, such as illness severity and the presence of comorbid anxiety symptoms are discussed. The results provide skepticism for the utilization of microstate alterations as an independent biomarker for MDD. Future research is needed to clarify the observed relationship between anxiety symptoms and microstate class E.