This paper provides an overview of cognitive neuroscience in the 20th century, and tries to suggest some directions for new research strategies for the 21st century. In the 20th century, cognitive neuroscience in a broad term was composed of neurophysiology, psychophysiology and brain modeling, each of which represents a research strategyy of microscopic analysis, behavioral studies and computational theories. Each discipline has made a great progress on its own, but it was only the last few years of the 20th century that the related disciplines began to interact with one another. For cognitive neuroscience in the 21st century, we expect neuroscience and behavioral science to fuse through modeling studies. A model is the abstraction of physical phenomenon. A brain architecture model that integrates abstracted neuroscientific evidence with abstracted behavioral scientific evidence will be the key for the fusion of both field evidence and interpretation. It is suggested that the the understanding of the process of language acquisition, i.e. that of both lexicon and grammar, as the process of neural circuit development will be one of the candidates that verifies the biological feasibility of such a brain model. Therefore, training not only in one's own field but also in a wide range of related disciplines will be indispensable for the researchers of cognitive neuroscience in the 21st century.