In mammals, and especially primates, the massive expansion of the cerebral cortex reduces the superior colliculus to a much smaller fraction of the whole brain.

In non-mammalian species the optic tectum is involved in many responses including swimming in fish, flying in birds, tongue-strikes toward prey in frogs, and fang-strikes in snakes.

[citation needed] The superior colliculus is associated with a nearby structure called the parabigeminal nucleus, often referred to as its satellite.

The intermediate and deep layers also receive input from the spinal trigeminal nucleus, which conveys somatosensory information from the face, as well as the hypothalamus, zona incerta, thalamus, and inferior colliculus.

There are two large descending pathways, traveling to the brainstem and spinal cord, and numerous ascending projections to a variety of sensory and motor centers, including several that are involved in generating eye movements.

Both colliculi also have descending projections to the paramedian pontine reticular formation and spinal cord, and thus can be involved in responses to stimuli faster than cortical processing would allow.

[16] The clearest indication of columnar structure comes from the cholinergic inputs arising from the parabigeminal nucleus, whose terminals form evenly spaced clusters that extend from top to bottom of the tectum.

[17] Several other neurochemical markers including calretinin, parvalbumin, GAP-43, and NMDA receptors, and connections with numerous other brain structures in the brainstem and diencephalon, also show a corresponding inhomogeneity.

[16] The functional significance of this columnar architecture is not clear, but it is interesting that recent evidence has implicated the cholinergic inputs as part of a recurrent circuit producing winner-take-all dynamics within the tectum, as described in more detail below.

Before about 1970, most studies involved non-mammals — fish, frogs, birds — that is, species in which the optic tectum is the dominant structure that receives input from the eyes.

The general view then was that the optic tectum, in these species, is the main visual center in the non-mammalian brain, and, as a consequence, is involved in a wide variety of behaviors.

[19] From the 1970s to 1990s, however, neural recordings from mammals, mostly monkeys, focused primarily on the role of the superior colliculus in controlling eye movements.

This line of investigation came to dominate the literature to such a degree that the majority opinion was that eye-movement control is the only important function in mammals, a view still reflected in many current textbooks.

This discovery reawakened interest in the full breadth of functions of the superior colliculus, and led to studies of multisensory integration in a variety of species and situations.

[20] Thus, cats with major damage to the visual cortex cannot recognize objects, but may still be able to follow and orient toward moving stimuli, although more slowly than usual.

This seems to contradict the observation that stimulation of a single point on the SC can result in different gaze shift directions, depending on initial eye orientation.

Although the SC receives a strong input directly from the retina, in primates it is largely under the control of the cerebral cortex, which contains several areas that are involved in determining eye movements.

The parietal eye fields, farther back in the brain, are involved mainly in reflexive saccades, made in response to changes in the view.

Heightened distractibility occurs in normal aging [37] and is also a central feature in a number of medical conditions, including attention deficit hyperactivity disorder (ADHD).

[44] It is usually accepted that the primate superior colliculus is unique among mammals, in that it does not contain a complete map of the visual field seen by the contralateral eye.

[45] This functional characteristic is explained by the absence, in primates, of anatomical connections between the retinal ganglion cells in the temporal half of the retina and the contralateral superior colliculus.

The visual receptive fields of neurons in the superior colliculus in these animals form a precise map of the retina, similar to that found in cats and primates.

[12] In a series of studies, researchers have identified a set of Ying-Yang circuit modules in the superior colliculus to initiate prey capture and predator avoidance behaviors in mice.

[56] By using single-cell RNA-sequencing, researchers have analyzed the gene expression profiles of superior colliculus neurons and identified the unique genetic markers of these circuit modules.

The optic tectum is closely associated with an adjoining structure called the nucleus isthmi, which has drawn a lot of interest because it evidently makes a very important contribution to tectal function.

In the optic tectum, the cholinergic inputs from Ipc ramify to give rise to terminals that extend across an entire column, from top to bottom.

Imc, in contrast, gives rise to GABAergic projections to Ipc and optic tectum that spread very broadly in the lateral dimensions, encompassing most of the retinotopic map.

The optic tectum is involved in many responses including swimming in fish, flight in birds, tongue-strikes toward prey in frogs, and fang-strikes in snakes.

[66] In snakes that can detect infrared radiation, such as pythons and pit vipers, the initial neural input is through the trigeminal nerve instead of the optic tract.

[70] In common with other systems (see [71] for a historical perspective of the idea), neural circuits within the spinal cord seem capable of generating some basic rhythmic motor patterns underlying swimming, and that these circuits are influenced by specific locomotor areas in the brainstem and midbrain, that are in turn influenced by higher brain structures including the basal ganglia and tectum.