The midbrain divides into the tectum and the cerebral peduncle. These deep brain structures lie just above the brain stem. In primitive vertebrates such as amphibians, fish, and reptiles, the tectum serves as the main visual processing center in the brain. In primates, its function is more restricted as the majority of visual processing is done in the neocortex. The primate tectum helps to control eye movement. In other words, it helps control eye movements. The cerebral peduncle includes several brain areas that contain the neurons that produce important neurotransmitters. For example, the substantia nigra is the origin of a major tract of dopamine neurons.