Input into the corpus striatum is received via projections from the cerebral cortex (corticostriatal fibers), intralaminar nuclei of the thalamus (thalamostriatal fibers), and the substantia nigra zona compacta (nigrastriatal fibers). While the cerebral cortex projects to an extensive area of the corpus striatum, which receives projections from motor, sensory, and association areas, the relationship between input and output sites of the cerebral cortex and corpus striatum tends to be constant. In contrast, output from the corpus striatum is sent to the pallidum (striatopallidal fibers) and substantia nigra zona reticularis (striatonigral fibers).
The external segments of the pallidum and subthalamic nucleus (Luys’ body) send reciprocal inputs and outputs (pallidothalamic and subthalamopallidal fibers). In addition, the external segment of the pallidum projects to the substantia nigra zona reticularis (pallidonigral fibers). In contrast, fibers project from the external segment of the pallidum to the thalamus through the ansa lenticularis and the lenticular fasciculus (pallidothalamic fibers).
The substantia nigra zona compacta projects to the amygdala and subthalamic nucleus (Luys’ body), and both the regions send feedback to the substantia nigra zona compacta, which interconnects with the frontal lobe. The substantia nigra zona compacta also receives input from the raphe nuclei, pedunculopontine nucleus, and medial pallidum. On the other hand, the substantia nigra zona compacta projects to the superior colliculus, ventromedial thalamic nuclei, and lateral ventral nuclei.