Sample dendrogram and topographical maps. Left: an example of a dendrogram as a result of the hierarchical clustering. The x-axis indicates EEG recording electrode sites. The y-axis represents the “distance” between cortical areas. The distance indicates how strongly signals from distant cortical areas are phase-locked (see Methods for details). Note that the geometry of electrodes in the topographical map did not factor into the calculation of the distance. Right: each topographical map is obtained from a corresponding clustering threshold (designated as a red dotted line) in the left dendrogram. Note that the colour itself does not have any meaning. Electrodes marked with “x” indicate clusters that have only one node.