Anatomical aspects of information processing in primate basal ganglia

Recent studies with double-anterograde tract-tracing methods have shed new light on the organization of the basal ganglia circuitry in primates. This paper briefly reviews some of these findings and provides a personal interpretation of their possible functional significance. Emphasis is placed on the fact that the striatum and the subthalamic nucleus have multiple representations in the two major output structures of the basal ganglia, namely the internal segment of the globus pallidus and the substantia nigra pars reticulata. It is hypothesized that this multiple representation serves as a means of amplifying and diversifying the striatal and subthalamic influences upon thalamocortical neurons that is mediated through the globus pallidus and the substantia nigra. Furthermore, evidence for the highly ordered organization of the striatopallidal and subthalamopallidal projections, which converge onto single pallidal neurons according to different but highly specific patterns, is taken as an indication that the subthalamic nucleus uniformly excites a vast collection of pallidal neurons, whereas the striatum exerts a more specific inhibitory control upon selected subsets of subthalamically driven pallidal neurons.