Introduction : background to the dynamics of the basal ganglia -- The striatum : functional significance, and direct connectivity to output nuclei of the basal ganglia -- The indirect pathways from striatum to basal ganglia output nuclei, and their relation to the direct pathway -- Theories of basal ganglionic function -- Synopsis of part I and predictions derived from it -- Huntington's disease -- Parkinson's disease and Parkinsonian syndromes -- Dopamine-dependent psychosis -- Syndromes arising as complications of Profilonged underactivity of striatal dopamine mechanisms, and other disorders of the basal ganglia -- Synopsis of part II and predictions derived from it.