Organization of the basal ganglia: the importance of axonal collateralization

Recent neuroanatomical data obtained with single-axon or single-cell labeli ng procedures in both rodents and primates have revealed the presence of va rious types of projection neurons with profusely collateralized axons withi n each of the major components of the basal ganglia. Such findings call for a reappraisal of current concepts of the anatomical and functional organiz ation of the basal ganglia, which play such a crucial role in the control o f motor behavior. The basal ganglia now stand as a widely distributed neuro nal network, whose elements are endowed with a highly patterned set of axon collaterals. The elucidation of this finely tuned network is needed to und erstand the complex spatiotemporal sequence of neural events that ensures t he flow of cortical information through the basal ganglia.