Fig. 1. A diagram to demonstrate the reductive approach of network topology. All of the physical details (distances, widths, gradients, surfaces, etc .) of the Königsberg city streets can be stripped away to leave only the important factors: four land masses (represented by green circles =“nodes ” or “vertices ” in modern parlance), and seven bridges (represented by red lines =“edges ” or “connections”). Similarly, the complexity of the anatomic connections between different cortical areas is ignored, and only the functional connectivity of activity (as detected via the scalp electroencephalogram) is analyzed. For illustrative purposes only, we have arbitrarily chosen a cortical topology that is the same as that of the Königsberg bridges. (We have, however, made the important nodes in the temporoparietal area rather than in the frontal area—in accordance with Lee's results.)