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The SC is involved in a lot of things.

Excitatory burst neurons (EBNs) in the paramedian pontine reticular formation (pprf) (pons) initiate saccades.

These neurons receive direct excitatory input from SC and inhibitory input from the nucleus raphe interpositus (RIP) (brainstem).

Wang et al. provide evidence that SC might during saccades turn of RIP inhibition through the central mesencephalic reticular formation (cMRF) while it drives EBNs.

A possible ascending pathway from SC to visual cortex through the pulvinar nuclei (pulvinar) may be responsible for the effect of SC activity on visual processing in the cortex.

There may be an indirect ascending pathway from intermediate SC to the thalamic reticular nucleus.

It has been found that stimulating supposed motor neurons in the SC facilitates visual processing in the part of visual cortex whose receptive field is the same as that of the SC stimulated neurons.

The superior colliculus is connected, directly or indirectly, to most parts of the brain.

Deep SC neurons which have preferred saccades have these preferred saccades also in total darkness. They thus do not simply respond to the specific location of a visual stimulus.

Robinson reports two types of motor neurons in the deep SC: One type has strong activity just (~20 milliseconds) before the onset of a saccade. The other type has gradually increasing activity whose peak is, again, around 12-20 milliseconds before onset.

The superficial SC projects retinotopically to LGN.

The same regions in LGN receiving projections from the superficial SC project to the cortex.

The excitatory and inhibitory connections from the deep to the superficial SC and the connection from the superficial SC to LGN may be one route through which deep SC activity may reach cortex.

There's a loop from cerebellum to SC and back.

There are ascending pathways from SC to the eye fields through talamic structures.

There is a disynaptic connection from SC to the dorsal stream visual cortex, probably through the pulvinar.

It has been found that stimulating supposed motor neurons in the SC enhances responses of v4 neurons with the same receptive field as the SC neurons.

The SC is involved in generating gaze shifts and other orienting behaviors.

There are ascending projections from the superficial SC to the Thalamus and from there to extrastriate cortex.

There are descending projections from the SC to the parabigeminal nucleus, or nucleus isthmii as it is called in non-mammals.

The deeper layers of the SC project strongly to brainstem, spinal cord, especially to those regions involved in moving eyes, ears, head and limbs, and to sensory and motor areas of thalamus.

Neurons in the deep SC whose activity spikes before a saccade have preferred amplitudes and directions: Each of these neurons spikes strongest before a saccade with these properties and less strongly before different saccades.

There are at least polysynaptic pathways from deep SC to cortex.

Polysynaptic pathways from deep SC to cortex may explain facilitation of visual processing in the V1 caused by SC

Hyde and Knudsen found that there is a point-to-point projection from OT to IC.

An SC output neuron which projects to some structure outside the SC may sample input from SC lamina according to the requirements of the target of its projections.

Benevenuto and Fallon found projections from the SC mostly to midbrain and thalamus structures. They did not study projections to cortical regions. In detail, they found projections to:

Midbrain:

  • inferior colliculus
  • pretectum

Thalamus:

  • ventral lgn
  • dorsal lgn
  • suprageniculate nucleus
  • intralaminar nuclei
  • parafascicular nucleus
  • parts of dorsomedial nucleus
  • suprageniculate nucleus
  • certain pulvinar nuclei
  • lateral posterior nucleus
  • reunions nucleus
  • ventral posterior inferior nucleus
  • ventral posterior lateral nuclei
  • ventral lateral nucleus
  • limitans nucleus

Hypothalamus

  • dorsomedial nucleus

Other

  • Fields of Forel (subthalamic)
  • zona incerta
  • accessory optic tract (in midbrain)

There seems to be an ascending pathway from superficial SC to the medial temporal area (MT) through the pulvinar nuclei (inferior pulvinar).

Berman and Wurtz found neurons in the pulvinar nuclei which received input from SC and sent output to MT.

Some models assume SC output encodes saccade amplitude and direction. In other models, each spike from a burst neuron encodes a motion segment, with length and direction depending on the position of the neuron and strength of connection to brainstem areas