Superior colliculus

At a glance

English

Superior colliculus

Latin (TA2)

Colliculus superior

System

Brain and spinal cord

Region

Head

Side

Paired, left and right

About the superior colliculus

The superior colliculi, Latin for upper little hills, are two rounded swellings on the back of the midbrain. With the smaller but more prominent inferior colliculi below them they form the tectal plate (quadrigeminal plate), the roof of the midbrain behind the cerebral aqueduct. The pineal gland rests in the hollow between the two superior colliculi, and the thalamus, with its pulvinar, overhangs them in front. From each colliculus a band, the brachium of the superior colliculus, runs forward and laterally, passing between the pulvinar and medial geniculate body, towards the lateral geniculate body and the optic tract.

The colliculus is built in alternating layers of grey and white matter, usually counted as seven. The superficial layers, the zonal layer, the superficial grey layer and the optic layer, are almost purely visual. They receive fibres directly from the retina through the brachium, mostly from the opposite eye, and from the visual cortex, and each holds a map of the opposite visual hemifield. The intermediate and deep layers take input from many sources, including the frontal eye fields and parietal cortex, the inferior colliculus for hearing, the spinal trigeminal nucleus for touch on the face, and an inhibitory projection from the reticular part of the substantia nigra that holds the colliculus in check until a movement is chosen.

Neurons in the deep layers are motor. A burst of activity at one point on the map triggers a rapid gaze shift, a saccade, often combined with a head turn, towards the matching point in space. These signals reach the brainstem gaze centres, including the pontine paramedian reticular formation, and the tectospinal tract carries orienting commands to the cervical cord. Because visual, auditory and touch maps are aligned, the colliculus can direct attention to an event before the cortex has recognised it.

Pressure on the tectal plate, typically from a tumour of the pineal region, impairs upward gaze and the pupillary light response in Parinaud syndrome. The colliculus is also involved in the control of distractibility, which may be relevant to attention disorders.

Function and supply

Function

Maps visual, auditory and touch space and triggers saccades, head turns and shifts of attention towards a target, with outputs to brainstem gaze centres, the cervical cord and the pulvinar.

Blood supply

The quadrigeminal (collicular) branch of the posterior cerebral artery and branches of the superior cerebellar artery.