Connection ( Bota et al. 2003 ) : The overall structural link between two nodes in the wiring diagram of the nervous system (Monro, 1783); synonyms include structural connection and projection. The nodes may be described at three successively greater levels of resolution and accuracy. For a macroconnection (Thompson & Swanson, 2010) the two nodes are gray matter regions, for a mesoconnection (Thompson & Swanson, 2010) the nodes are neuron types (Bota & Swanson, 2007), and for a microconnection (Thompson & Swanson, 2010) the nodes are individual neurons (Waldeyer, 1891). A node can establish one or more connections that are either an intranodal connection(s) or an internodal connection(s). An axon connection is unidirectional, whereas an amacrine connection (amacrine extension connection) is bidirectional. The physical course taken by a connection through gray matter regions and white matter tracts is called its route, and route information is part of the description of a connection. Information about a set of connections can be arranged in a number of different ways like a wiring diagram, connectome, or basic plan. A closely related concept is pathway-the part of a connection demonstrated in a particular experimental analysis; another related term is functional connection. "Connections" between parts of the vertebrate brain (Cuvier, 1800) were described at least as early as Gordon (1817, p. 134); for its use as defined here see Bota et al. (2003, p. 795). Also see connections.