Neuroscience Study Questions - Gaze Control

Saccades

Rapid steplike eye movement used to acquire and image on the fovea

• Speed 700-900 degree per second

• 5000º per sec² (elevates)

• Conjugate (same direction)

Smooth Pursuit Movement

Head is Stationary  

• Allows you to maintain a fixed gaze on a target as it moves (can only occur w/a target)

• Slow phase eye movement (can generate with auditory target too) 

• Only works for tracking objects up to ~100-120º per second (any faster it doesn’t work - start to lag)

• Conjugate (same direction)

Vestibulo-Ocular Reflexes (VOR)

Reflex responsible for holding image on fovea during head movements. 

• Very short latency. 

• Occurs in all directions of head movement. 

• Conjugate (same direction)

Optokinetic Movement

Used to track and re-aquire moving images.

• Best though of a combination of smooth pursuit tracking and saccadic re-acquisition 

• Combination of slow & fast pace movements (smooth pursuit → Saccade)

Vergence

Used to get or keep objects at different distances centered on the fovea. Convergence for near objects, divergence for distance objects.

• Only type of disconjugate eye movement 

• Cross-Eyed 

• Accommodation (Convergence + Constriction)

• Dipolia = Double vision (caused by eyes drifting apart)

Fixation

Maintenance of focus on an object.

• Requires active suppression of other movements 

• No eye movement  (neither conjugate or disconjugate)

Why is the fovea important to gaze control

Central portion of retina, contains only cones and is specialized for color vision with the highest acuity 

• Keep whatever we are looking at centered at the fovea

Why is gaze important in gaze control

The control of eye and head movement to direct the fovea to an image of interest

Gaze System (2 components)

Oculomotor system and head movement system and head movement system with the goal to keep an image of interest centered on the retina

Cortical Areas

Frontal eye field/visual cortex, reticular formation (CN III, IV, VI), superior colliculi, Basal Ganglia, cerebellum

What are the cerebellar regions associated with saccades

• Oculomotor Vermis

• Coordinates fast phase eye movements

What are the cerebellar regions associated with smooth pursuit

• Flocularnodual Lobe/IZ:

  • Also VOR and vengeance 

• Coordination of Slow phased eye movements

If someone has a basal ganglia dysfunction what might we expect to observe on a test of saccades? Cerebellar issue?

• In normal vision what asking to look at a pen and nose there is a smooth transition between the two 

• In basal ganglia dysfunction we would expect to see dysmetria (difficulty with fine-point accuracy, with 2+ corrections)

• This is associated with the vermis in the cerebrum. 

CNS Centers Responsible for Types of Eye Movement: Saccades (oculomotor movements)

• Frontal eye field - Don’t need visual target → Superior colliculi → Reticular formation (CN III, IV, VI) ← Also getting input from oculomotor vermis (OV) 

CNS Centers Responsible for Types of Eye Movement: Smooth Pursuit (oculomotor movements)

• Actually a movement triggered by cerebellum

• Visual cortex → frontal eye field → cerebellum (FNL) → CN III, IV, & VI → Requires a target

CNS Centers Responsible for Types of Eye Movement: VOR (Reflex)

Vestibular apparatus → VNC → MLF → CN III (ipsilateral), CN VI (contralateral), CN IV (Up & Down) → LR, MR, or SO

CNS Centers Responsible for Types of Eye Movement: Vergance (oculomotor movements)

Visual cortex → Sup. Colliculi (bilateral input) → Exits CN III (Inhibit IV and VI)

CNS Centers Responsible for Types of Eye Movement: Fixation (oculomotor movements)

Descending suppression from B.S. areas, cerebellum from visual cortex, and frontal eye fields.

Areas Associated With Gaze Control: Frontal Eye Fields/Superior Colliculus

• Inhibition of Saccades, to control vergance and fixation 

• Organize smooth pursuit → Movement from both eyes are equal 

Areas Associated With Gaze Control: Pontine/Medullary Reticular Formations

• Inhibition of Saccades, to control vergance and fixation  

• Triggered in CN III, IV, & VI

Areas Associated With Gaze Control: Basal Ganglia/Cerebellum

• Amplitude & Speed of Movement Through Cortical Drive 

• Amplitude & latency of saccades 

• Cerebellum = Pin-point accuracy