FIGURE 1.

Schematic illustrating the method of topographic segmentation using 1 s of 81‐channel eyes‐closed rest taken from an individual electroencephalogram (EEG) recording at random. (a) The global field power (GFP) is calculated from the multichannel EEG and reflects a measure of the ongoing strength of the electric field. The time series succession of voltage maps is also derived from the EEG. Maps are 2D isometric projections with nasion upward. (b) Voltage maps at peaks of GFP are identified as periods of topographic quasi‐stability. k‐means clustering of maps at GFP peaks (polarity is ignored) identifies the optimal k clusters of voltage maps for that recording. The centroids of clusters from each recording are then submitted to a second k‐means clustering to identify the optimal k global clusters from among all recordings. (c) The original EEG time series is categorized according to which global cluster centroid best correlates with that instance in order to reexpress the multichannel EEG as a sequence of alternating microstates and derive measures of temporal dynamics from the categorized time series