The central nervous system consists of gray matter structures, including the neocortex, basal ganglia, thalamus, and cerebellum, and an extensive array of connecting white matter tracts that allow the integration of the many functions mediated by the gray matter. Neuroscience, neurology, and behavioral neurology have tended to emphasize gray matter function and have left white matter disorders and the essential behavioral functions of white matter relatively unexplored. Individual diseases such as multiple sclerosis have been studied extensively, but an integrated view of the function of white matter and patterns of dysfunction occurring when white matter is affected has been lacking. In this resource, the author redresses this imbalance and provides a detailed discussion of the biology of white matter, the phenomenology of white matter diseases, and the pathological disturbances that affect primarily the white matter. The book discusses how great an effect white matter diseases have overall, contributing to many disease processes and providing the neurobiological basis for many cognitive disturbances.