Anatomical distinctions between the two basal ganglia afferent territories in the primate motor thalamus

In primates, the efferents of the two basal ganglia output structures, medial globus pallidus and substantia nigra pars reticularis, are completely segregated and target different thalamic regions. Despite similarities demonstrated earlier in nonprimate species in the functional properties and ultrastructural features of the terminals of the two pathways, the present findings suggest significant differences between thalamic circuits associated with the two systems in primates. The data presented in this report further support the concept on functional and anatomical diversity of the subdivisions of the primate motor thalamus proposed in 1990 by Hinsky.