The fundamental similarities between various neocortical areas are elaborated by pointing out the common principles of its afferent, intrinsic, and efferent organization, with special emphasis on the generality of thalamocortical circuits. Interareal differences in morphology and function can be considered as accidental, i.e., depending on the circuit in which a given cortical area is involved. The neocortex is a link in the chain of afferent-efferent signal processing, and can be understood as a cooperative network that acts as a nonlinear spatiotemporal filter with adaptive properties (memory) and that transforms afferent signal flow. It is assumed that these filter properties are identical for all neocortical areas. The functional role of a circumscribed cortical area depends exclusively on its position uithin a certain functional circuit and is defined by it.