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Smooth Pursuit (Eye Movements)
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Smooth Pursuit (Eye Movements)

Smooth Pursuit
OVERVIEW
  • Smooth pursuit eye movements allow us to keep a moving target in our fovea and clearly visualize it.
  • Each cerebral hemisphere is responsible for ipsilateral smooth pursuit eye movements, meaning that the right hemisphere detects and tracks images as they move to the right and the left hemisphere detects and tracks images as they move to the left.
  • Within the circuitry for smooth pursuit, the contralateral cerebellum and medulla and the ipsilateral pons are incorporated via a double decussating pathway.
CIRCUITRY
  • M retinal ganglion cells detect the target movement.
  • Visual detection of the target's movement from left to right is projected from the retinae to the right lateral geniculate nucleus and then to the right primary visual cortex (V1) (calcarine sulcus).
  • The primary visual cortex projects to visual area V5 (the human homologue to the macaque middle temporal [MT] area), which then projects to visual area V5a (the human homologue to the macaque medial superior temporal [MST] area).
    • In humans, both V5 and V5a lie at the temporo-occipito-parietal junction.
Visual area V5a projects to the posterior parietal cortex (parietal lobe), which projects to the frontal eye fields (think: posterior middle frontal gyrus*).
  • The frontal eye fields (and other cortical visual areas, as well) project to the ipsilateral dorsolateral pontine nuclei (DLPN) in the high pons and the ipsilateral nucleus reticularis tegmenti pontis (NRTP) in the upper pons.
    • As an example, the RIGHT DLPN and right NRTP project across midline to the LEFT side of the cerebellum, specifically to the flocculus and paraflocculus of the vestibulocerebellum and also to the dorsal vermis.
  • The vestibulocerebellum and dorsal vermis project to the ipsilateral medial vestibular nucleus in the medulla.
  • The left medial vestibular nucleus projects to the contralateral abducens nucleusin the right mid- to low pons, which completes the double decussation.
    • The right abducens nucleus then initiates horizontal pursuit eye movements to the right.
ANATOMY
Pons
  • The abducens nucleus of cranial nerve 6 lies near midline within the posterior tegmentum of the mid- to low pons.
  • The NRTP lies in the anterior, midline tegmentum of the upper pons.
  • The DLPN lies within the posterior lateral aspect of the high pontine basis.

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