Four colliculi, two superior and two inferior, that sit on the quadrigeminal plate on the posterior midbrain. Functionally, they serve as reflex centers involving vision and hearing. The superior colliculi is involved with visual processing and the inferior for auditory processing. The superior colliculi projects to the lateral geniculate nucleus of the thalamus, which relays visual information to the primary visual cortex. The inferior colliculi projects to the medial geniculate nucleus, which relays auditory information to the primary auditory cortex. Both colliculi also have descending projections to the paramedian pontine reticular formation and spinal cord.