Eye Movement and Sensorimotor Integration

Question 1

Why do we move our eyes?

Answer 1

High visual acuity restricted to a small area (the fovea)

Eye movement direct the phobia to objects of interest, or ‘foveate’

You can learn a whole lot about how people are acquiring information by examining their eye movements

Also incredibly important as a clinical assessment tool

Question 2

“foveate”

Answer 2

keeping our fovea on the object of interest to gain information about features of the object

Question 3

How do we move our eyes?

Answer 3

Three antagonistic pairs of muscles control eye movements

• Lateral and medial rectus
• Superior and inferior rectus
• Superior and inferior oblique

We have three axes of eye movements

• Horizontal, adduction and abduction (towards or away from the nose)
• Vertical, elevation or depression (up or town)
• Torsional, intorsion or extorsion (towards or away from the nose)

Question 4

Extraocular muscle innervation

Answer 4

Extraocular muscles

Innervated by lower motor neurons in cranial nerves

• Abducens (VI): Lateral rectus
• Trochlear (IV): Superior oblique
• Oculomotor (III): All the rest, plus eyelid, pupillary construction (medial rectus, superior, inferior rectus, and inferior obliques)

Question 5

Name the 5 basic types of eye movements

Answer 5

Gaze

Stabilize

Saccades

Smooth Pursuit

Vergence

Question 6

Gaze

Answer 6

moving eyes to an object of interest

via saccades, smooth pursuit, vergence

Question 7

stabilizing eye movements

Answer 7

keeps eyes on object of interest

vestibuloocular or optokinetic movement

Question 8

Describe saccades

Answer 8

• Rapid
• Ballistic (…well not really, but we can pretend)
• Change the direction of fixation
• Can be small (like when reading) or large while searching a visual scene
• Can be voluntary or reflexive
• Occur during REM sleep

Question 9

How long does a saccade take?

Answer 9

200 ms to process, 80 ms to actually move eyes

Question 10

Describe smooth pursuit eye movements.

Answer 10

Slower tracking movements

Used to keep fovea on target

sort of voluntary

• we can choose whether to track an object, but require training to smooth pursuit without a target.

Question 11

Describe smooth pursuit’s speed limit.

Answer 11

We have catch-up saccades to get to where the object is if it’s moving faster than we can smooth pursuit.

Once they’re oriented, and if the object is moving slowish, we can smooth pursuit right along with the object movement.

Question 12

Describe vergence eye movements

Answer 12

Align the fovea of each eye with targets located at different distances

Most common when shifting gaze between objects of different depths

Disconjugate movements

Question 13

Describe VOR/ OKN types of movements

Answer 13

Operate together

Move the eyes to stabilize gaze relative to the external world

Compensate for head movements

Prevent retinal slipping (object getting outside of foveal vision)

VOR is based on sensory information from the semicircular canals

OKN is based on large portions of the visual field moving

Looking out a car window (optokinetic nystagmus): typewriter example

Question 14

VOR is a reflection of ____ movement, while OKN is a reflection of _____ movement.

Answer 14

self; world

or

fast; slow

Question 15

The brain controls what two aspects of a saccade? What allows the brain to know the amplitude of the saccade?

Answer 15

Brain needs to accomplish two tasks

1. Control direction of saccade
2. Control amplitude of saccade

Amplitude is coded by the duration of neuronal activity within the oculomotor nuclei

Question 16

Neural control of saccades: how is direction of eye movement determined?

Answer 16

Direction is determined by which eye movements are active

Controlled by local neuron circuits in two gaze centers

• Paramedian pontine reticular formation (PPRF or horizontal gaze center)
• Rostral interstitial nucleus (vertical gaze center)

Activating each system separately results in uni-axis movements

PPRF also sends axons to medullary reticular formation, to inhibit contralateral muscles

“etch-i-sketch”

Question 17

neuron control of saccades: how is the location of the stimuli transformed to appropriate activity in gaze center?

Answer 17

Our old friend the superior colliculus

Several frontal and parietal lobe regions

FEF, MEF, SEF, DMFC (Frontal)
LIP, MT, MST (Parietal

Superior colliculus and FEF contain topographical maps

Question 18

How does the cerebral cortex play a role in neural control of saccades?

Answer 18

Cerebral cortex regions concerned with eye movements collaborate with superior colliculus in controlling saccades

• FEF, for example, can control eye movements by activating selected populations of SC neurons

Cerebral cortex regions also can control eye movements directly

• FEF –> Contralateral gaze centers

Allows for some sparing of eye movements following damage!

• To either cerebral cortex or brainstem

Question 19

Describe the neural contro of smooth pursuit eye movements.

Answer 19

We have it easy

Once thought to be mediated by different structures (more to know!)

Now, it is believed that smooth pursuit is controlled by many of the same structures as saccades

• Gaze centers, SC, Frontal and Parietal eye movement regions

Neurons in striate and extrastriate cortex provide sensory information necessary to guide smooth pursuit

Damage to occipital and parietal lobes can result in abnormalities in smooth pursuits (sobriety test)

Question 20

Neural control of vergence.

Answer 20

We know very little about how these movements are performed

Information about location of retinal activity is relayed through the LGN to cortex, where information from the two eyes is integrated

Amount of binocular disparity is used by extrastriate regions to determine whether eyes should diverge or converge

Information sent to vergence centers in the brain stem

• Some populations of neurons command convergence movements, others divergence movements

Question 21

Describe sensorimotor integration within the superior colliculus

Answer 21

Superior Colliculus

Superficial visual layer and deeper motor layer

Visual and motor maps were are in register

• Visual cells that respond to a certain region of space are connected to deep layer that controls eye movements to the same region