Malfunctions of the basal ganglia cause movement disorders, such as Parkinson's disease and dystonia. Several models have been proposed to explain the pathophysiology of these disorders: (1) Firing rate model: activity imbalance between the direct and indirect pathways changes the mean firing rate of output nuclei of the basal ganglia and induces hypokinetic or hyperkinetic movement disorders; (2) Firing pattern model: oscillatory and/or synchronized activity observed in the basal ganglia disturbs information processing in the basal ganglia, resulting in motor symptoms; (3) Dynamic activity model: movement-related activity changes through the direct and indirect pathways disrupt balance between movement-related inhibition and surrounding excitation in the output nuclei, and induce motor symptoms. Each model will be critically discussed in this review.
