PROJECTIONS OF THE PALLIDAL COMPLEX - AUTORADIOGRAPHIC STUDY IN THE CAT

The efferent projections of the external pallidal segment ('globus pallidus'), and the internal pallidal segment (entopeduncular nucleus) were studied in separate experiments in the cat by the auto-radiographic tracing method. Injections of tritiated amino acids into the external pallidal segment resulted in labelling of axon systems distributed not only to the subthalamic nucleus but also in sparser density to the nucleus reticularis thalami, the substantia nigra, the caudate nucleus, the putamen, and as yet undefined areas of the cortex. Injections of tritiated amino acids into the internal pallidal segment resulted in labelling of axon systems distributed to the ventrolateral-ventroanterior complex of the thalamus, to the centrum medianum, the lateral habenular nucleus, and the mesencephalic nucleus tegmenti pedunculopontinus, pars compacta. Less prominent termination may also occur in the parafas-cicular nucleus, the nuclei of the fields of Forel, and in the mesencephalic tegmentum rostral to the nucleus tegmenti pedunculopontinus, pars compacta. The fact that this and previous studies show that the projections of the pallidal complex are more widespread than would be expected if it was only involved in motor functions, raises questions about the functional organization of the basal ganglia. These are discussed in the following paper. © 1979.