Subcortical projections of the parietal lobes.

Parietal lobe visual areas project to several subcortical targets. Three of the most prominent of these are to the basal ganglia, superior colliculus, and pontine nuclei. All three are probably involved in some aspect of visually guided movement. One of the largest systems of fiber connections in the human brain arises in the cerebral cortex, and relays to the cerebellum via the pontine nuclei. Pontocerebellar axons terminate within the cerebellar cortex as mossy fibers. Cells in the cerebral cortex that project to the pontine nuclei are all pyramidal in shape, and all are located in lamina V of the cerebral cortex. Subcortical projections from the somatosensory cortex of rats shows that cells that project to the basal ganglia and cerebellum occupy different sublaminae of layer V. Some cortical pyramidal cells' axons may divide, with one branch projecting to the superior colliculus, the other to the pontine nuclei. Temporal lobe visual areas, which are involved in form recognition and learning, do not project to the cerebellum. Reciprocal connections from the cerebellum back to the parietal lobe may play a role in converting visual information from retinotopic to head-centered coordinates.