The brain, of course, is also a network. With perfect knowledge, one could define a brain network composed of billions of interconnected neurons, with a (general) hierarchical arrangement of, for example, cortical neurons into columns, functional areas (e.g., V1, V2), and functional systems (e.g., visual or somatosensory systems) (Churchland and Sejnowski 1991). Just as economies may be described as interactions between people, between cities, or between nations, brain networks may be described as interactions between neurons, between functional areas, or between functional systems.
