Intro arrow 4. SC: Superior Colliculus
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4. Superior Colliculus

As we navigate through our surroundings, a continuous stream of light images impinges on our eyes. In the back of each eye is a light-sensitive tissue, the Retina, it converts patterns of light energy into electrical discharges known as action potentials. These signals are conveyed along the axons of retinal ganglion cells to connect for 20% to the SC (Superior Colliculus) and for 80% to the LGN.


The Superior (SC) and Inferior (IC) Colliculi are 2 pairs, known collectively as the Corpora Quadrigemina (CQ / Latin, quadruplet bodies). The Superior Colliculus (Latin: higher hill) is a part of the Tectal Area (Latin: roof) of the dorsal part of the Midbrain, a junction of the Gray and White Matter. The CQ receives visual, as well as auditory, inputs in its layers and they are connected to many sensorimotor areas of the brain. The CQ as a whole is there to help orient the head and eyes toward something seen and heard.


  • The Superior Colliculus (SC): Visual processing, and control of eye movements.
  • The Inferior Colliculus (IC): Auditory processing.

SC is involved in the generation of Saccadic eye movements and eye-head coordination.

  • Input from: Cerebral Cortex, Inferior Colliculus, Retina, Basal Ganglia, and Spinal Cord.
  • Projections to: The Paramedian Pontine Reticular formation (PPRF), Spinal Cord, and elsewhere. Signals from the Midbrain go via the Thalamus to the Cerebral Cortex for interpretation. Descending projections to the PPRF and Spinal Cord can be involved in responses to stimuli faster than Cortical processing would allow, it can also mediate Oculomotor Movements without Cortical involvement.

SC is organized into 7 alternating Fibrous and Cellular layers, further categorized into Superficial and Deep:


A. Superficial Layers:

  • Stratum Zonale (SZ)
  • Stratum Griseum Superficiale (SGS)
  • Stratum Optican (SO)


B. Deep Layers:

  • Stratum Griseum Intermedium (SGI)
  • Stratum Album Intermedium (SAI)
  • Stratum Griseum Profundum (SGP)
  • Stratum Album Profundum (SAP)

SC transforms signals from several sensory systems into motor commands for guiding orienting responses of eyes and head.




From almost exclusively Vision areas.



  • Contralateral
  • Non color opponent Retinal ganglion cells


Cortical: V1

  • Layers V and VI
  • 6 visual cortical regions (areas 17, 18, middle temporal, dorsomedial and medial areas and the posterior parietal region).


Cortical: Extra-striate Cortex

  • Layer V of areas 18, 19, FEF, and pre-motor cortex.


To areas involved in Vision.

  • Parabigeminal Nucleus (ipselateral)
  • Pretectum
  • Inferior Pulvinar Nucleus
  • Magnocellular dorsomedial nucleus of Thalamus
  • LGN (Dorsal and Ventral)



- From sensory modalities:

Visual, Auditory and Somatosensory.

- From motor areas and projections from

areas neither purely motor nor sensory.



  • Layer V of FEF
  • Prefrontal association cortex
  • Inferior bank of intraparietal sulcus
  • Layer V of temporal and occipital lobe



  • Substancia Nigra (Basal Ganglia)

Ascending projections:

To areas for Saccadic eye movements.

  • Dorsal Thalamus -> FEF and inferior parietal lobule.
  • Rostral Interstitial Nucleus of the medial longitudinal fasciculus.
  • Oculomotor complex
  • Magnocellular division of the ventral anterior nucleus
  • Paralamellar region of the mediodorsal nucleus
  • Parafascicular nucleus

Descending projections:

To Brainstem areas that have direct connections to motor neurons in neck. Projections thought to be involved in controlling eye movements

  • Nucleus reticularis tegmenti-pontis
  • Nucleus reticularis pontis oralis
  • Cell groups central and medial to the abducens nucleus
  • Medial accessory nucleus of the inferior olivary complex

Reseaches found that:

  1. MT and V3 are disynaptically connected to the SC, but V2 is not.
  2. The majority of labeled cells are in Layer 2b of SC, a zone that projects heavily to the inferior Pulvinar. Few labeled cells are found in Layer 2a, the zone that projects to LGN.
  3. The main route of SC disynaptic projections is likely to go through PIL and Plm, subdivisions that may both project to MT and V3, but not V2

This disynaptic colliculo-cortical pathway may be a unique feature of "dorsal stream" visual areas.



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