Oculomotor IV Smooth Pursuit Flashcards
What is smooth pursuit? What brain areas does the it involve?
The brain must calculate the target velocity and convert (sensory motor transformation) into eye velocity
Includes the dorsal stream through extrastriate cortex (area MT), frontal eye fields, pontine nuclei, cerebellum, and brainstem
What is vergence? What areas of the brain does it involve?
- only eye movement where the two eyes dont move together (disconjugate command)
- converge for close, diverge for far
Dorsal visual stream computes retinal disparity, pathway through frontal eye field to the midbrain vergence center
What is the smooth pursuit system?
- smooth eye movement requires a small moving stimulus
- goal is to lock the fovea onto the moving target to follow it
- requires attention (you have to want to follow it)
- brain must convert target velocity (T dot) into eye velocity (E dot) command
- eye position signal (E) is derived from neural integrator and final common path
What is a catch up saccade for?
Occurs when we are trying to move at the same velocity of the target. The fovea is far behind from the target, so we generate a catch up saccade that puts the fovea on the target.
Why are we not immediately following the target movement?
When the target is moving at a different velocity, the neurons in MT extract signal that generates eye velocity (E dot) signal to the brain, but this takes time. They eventually start to match.
Why is MT critical for smooth pursuit?
because it is the place that is extracting target velocity (visual motion)
________ eye movements required to fixate upon objects at different depths
disconjugate
Binocular disparity is the signal extracted from the _______ stream of extrastriate cortex and sent to the __________
Binocular disparity is the signal extracted from the DORSAL stream of extrastriate cortex and sent to the FRONTAL EYE FIELD
Motor commands for vergence descend to the __________________ and ________________
Motor commands for vergence descend to the midbrain reticular formation and pretectum.
Distal object falls ______ to the fovea on the retina.
Close object falls _______ to the fovea on the retina.
Distal object falls MEDIAL to the fovea on the retina.
Close object falls LATERAL to the fovea on the retina.
Describe what is involved in vergence movement.
Internuclear neurons get in the way, they will never let you do a vergence movement, want the eyes to always move in the same directions.
Vergence neurons project to the medial rectus motor neurons on both sides
- Tries to overcome/override the signal that is trying to move the two eyes together. It makes these two eyes pull in convergence movement.
- Also inhibited by OPNs (which inhibited all the saccade movements too)
- Vergence movement is slow because the OPNs are still active and not letting the saccades happens
But usually the movement is a combination of vergence and saccade (when there’s a saccade, the OPNs are shut off, which makes the vergence go a lot faster. Therefore vergence movement coupled with a saccade makes it go really fast)
What do OPNs inhibit?
Excitatory and inhibitory burst neurons along with convergence and divergence neurons
