Fig. 1.

Method of microstate analysis. A. The patient's high-density EEG (256 channels) at rest (eyes closed), after standard preprocessing, is displayed as a time series of global field topographies, showing quasi-stable periods between irregular changes (B.). C. The peaks of global field power (GFP) were determined and their specific topographies were selected and submitted to a k-means clustering procedure, for each individual participant, and in a second step across all participants (D.). E. This resulted in a set of four most representative topographies for all participants in both groups equally, the four microstate classes. Only the topography's relative configuration but not its polarity is considered. These four template topographies are then fitted back to the original EEG recording of each individual participant resulting in a labelling of the whole recording according to predominating microstate class. G. The resulting fine-grained time sequence of the labels is called the microstate sequence and used for statistical analysis.