While much currently remains unknown in the field of Parkinson’s research, this book assembles all that is currently known about the pathophysiological changes underlying Parkinson’s Disease (PD). It aims to integrate key aspects of current PD knowledge and research, specifically how disruptions of the non dopamine systems resulting from chronic dopaminergic degeneration could lead to the functional alterations observed in parkinsonism. The understanding of these mechanisms interactions and a proper analysis of the input-output transformations within the cortico-basal ganglia circuitry will contribute to the unveiling of important dynamic features of information processing in the PD brain.