[Recent advances in research on basal ganglia. Introduction]

The basal ganglia consist of the striatum, globus pallidus, substantia nigra, and subthalamic nucleus. Further, the striatum is classified into the caudate nucleus and the putamen; the globus pallidus, into the external (GPe) and internal segments (GPi); and the substantia nigra, into the pars compacta (SNc) and pars reticulata (SNr). With regard to the framework of information flow, the striatum constitutes the input station of the basal ganglia, and both the GPi and SNr constitute the output stations. Dopaminergic input from the SNc modulates the activity of striatal neurons. In the basal ganglia, there is a direct pathway that links the input and output stations and an indirect pathway that connects these stations by way of the GPe and the subthalamic nucleus. These 2 pathways regulate the net activity of the basal ganglia, thus providing the processed information to output targets, such as the thalamus.