L45 - Eye movement Flashcards by Max Kam

Importance of eye movement?

Highvisualacuityisrestrictedtothefovea

2. Eyemovementscandirectthefovea to newobjectsofinterest-“foveation”

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Pathways for pupillary constriction and dilation?

In bright light:

parasympathetic stimulation on circular (constrictor) muscle of iris runs circularly
pupillary constriction

In dim light,

sympathetic stimulation on radial (dilator) muscle of iris runs radially
pupillary dilation

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List the 5 types of eye movements? Classify into 2 categories?

Gaze-shifting movements (voluntary/ attention)
(1)Saccades (2)Smoothpursuit (3)Vergence

Gaze‐stabilizing movements (Reflexive)
(4)Vestibulo‐ocularreflex (5)Optokineticreflex

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Innervation of the extraocular muscles?

Superior oblique = CN IV Trochlear

Lateral rectus = CN VI Abducens

All the rest: Superior rectus,Inferior rectus, Medial rectus, Inferior oblique = CN III Oculomotor

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Describe saccadic eye movement? Is it voluntary or not?

Voluntary Rapidmovements ofbotheyes in the same direction betweentwophasesof fixation(conjugateeyemovement)
+
Verysmallmicro‐saccades(involuntary) to prevent fading

Drivenmainlybypositionsignals

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Time course of saccadic eye movement?

Timecourse:200‐250ms

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Describe smooth pursuit movement? Is it voluntary or not?

Slow,smootheyemovementsusedtotrackmoving objectsoncefoveation isachieved

Quasi-voluntary:
 Can choose whether or not to track a moving stimulus, but
 Cannot voluntarily generate smooth pursuit in the absence of a moving target

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2 basic response phases of smooth pursuit eye movement?

Pursuit initiation (= open-loop phase ~0.1s: catchup saccade)
Pursuit maintenance (driven by velocity error / retinal slip: alternative focus + out-of-focus)

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Describe Vergence eye movement? Is it voluntary?

disconjugate movements used to converge the eyes onto targets at different distances

Reflexive + voluntary components

Convergence of lines of sight of each eye to see an object that is nearer
Divergence of lines of sight of each eye to see an object that is father away

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What drives vergence eye movements?

binocular disparity of a target to be fixed

> > align the fovea of each eye with targets located at different distance

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Which of the gaze-shifting eye movements are opposite in action?

Vergence = Disconjugate eye movement

Saccadic = conjugate eye movement

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Function of vestibular-ocular reflex?

stabilize the eyes on a target during rapid head movements

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Describe the eye movements in vestibular-ocular reflex?

Vestibular system detects brief, transient changes in head position

> > Eye moves in opposite direction to head

> > preserves image on the center of visual field

> > physiologic nystagmus

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What are the 2 forms of vestibular-ocular reflex and which organs are involved?

Rotational VOR: driven by signals from the semi-circular canals which sense head rotations
Translational VOR: driven by signals from the otolith organs which sense linear head acceleration

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Describe the reflex arc in vestibulo-ocular reflex?

Stimulus = head movement
Afferent = vestibular nerve
Center = vestibular nucleus
Efferent = oculomotor nerves, abducens nerves
Effector = extra-ocular muscles

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Describe the neuronal control pathways in the right semi-circular canal when the head turns right?

endolymph turns from right to left due to inertia

> > depolarize hair cells
action potential to nerve, Scarpa’s ganglion
medial part of ipsilateral vestibular nucleus
medial longitudinal fasciculus:

Contralateral abducens nucleus (VI) = stimulate contralateral lateral rectus

Ipsilateral oculomotor nucleus (III) = stimulate ipsilateral medial rectus

> > > > > Eyes focus on left

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Describe the neuronal control pathways in the left semi-circular canal when the head turns right?

endolymph turns from right to left due to inertia

> > hyperpolarize hair cells
less action potential to nerve, Scarpa’s ganglion
medial part of ipsilateral vestibular nucleus
through medial longitudinal fasciculus

Contralateral abducens nucleus (VI) = inhibit contralateral lateral rectus

Ipsilateral oculomotor nucleus (III) = inhibit ipsilateral medial rectus

> > > > > Eyes focus on left

Describe the VOR suppression test?

Visual fixation on outstretched hands + rotate chair from side-to-side

Normal = eyes remain fixed on outstretched hands

Abnormal = eyes move in opposite direction to rotation with catch-up saccades to re-fix gaze on outstretched hands

Describe the Caloric reflex test for comatose patients?

 Head tilted back 60o

 horizontal canals of reclining patient are nearly vertical

 Warm water on right causes ampullofugal flow in right horizontal duct = action potential

 Cold water on left causes ampullopetal flow in left horizontal duct = less action potential

Function of Optokinetic eye response? Is it voluntary?

stabilizetheeyesduringheadmovements

Drivenbyretinaslip(likepursuit)but reflexiveandinvoluntary.

Optokinetic eye response work with which other eye movement?

TheVORandoptokineticsystems actinacomplementary.

Operateeffectivelyinresponsetoslow (below1Hz)headmovements,wheretheVORhaslowgain.

Together,theykeepthe eyesontarget

Describe optokinetic nystagmus?

alternatingslowandfastmovement oftheeyesinresponsetoanystimuli

Which side of the cortex processes which side of the visual field?

Left half of visual cortex receives information from the right half of the visual field/ left half of retinal yield of both eyes

Right half of the cortex receives information from the left half of the visual field/ right half of retinal field of both eyes

Describe the motor neuronal activity in saccadic eye movement? (think is the AP constant?)

‘Burst-tonic’ neuronal firing pattern

Abducens neuron fires a burst of activity that precedes the movement > move eye into position

In between saccades, these neurons have tonic firing > maintain static eye position

Which 3 main brain areas are involved in selecting visual targets for saccades and planning the movements?

(a) Superior colliculus (b) Frontal eye fields (c) Lateral intraparietal area

What are the 2 'fields' processed in the visual pathway brain regions?

spatially overlapping: (a) Visual receptive field: region of space in which visual stimuli activate cell (b) Movement field: a region of the visual field for which the neuron responds BEFORE execution of a saccadic eye movement

Compare the brain areas that modulate visual signals vs sensory and attentional signals?

- Visual signals = dorsal spatial vision pathway in occipital lobe - Sensory and attentional signals = frontal eye field near frontal lobe - Initiation and coordination of eye movement = superior colliculus + oculomotor centers in reticular formation + vestibular nuclei

Describe the place code for saccade vectors and the 3 types of neuronal response to onset of visual target?

In SC, FEF, the saccade vector produced by microstimulation = same independent of starting eye position 3 types of responses of neurons in all three areas (a) Visual neurons: respond briskly to onset (b) Visual/movement neurons: brisk response to visual target + burst of activity beginning right before saccade (c) Movement neurons: no visual response but clear burst of activity around saccade

Describe the visual neuron response to onset of visual target? Activity before saccadic eye movement?

respond briskly to onset of visual target in receptive field No burst of activity around time of saccade

Describe the visual/ movement neuron response to onset of visual target? Activity before saccadic eye movement?

brisk response to visual target and also burst of activity beginning right before saccade

Describe the movement neuron response to onset of movement target? Activity before saccadic eye movement?

no visual response but clear burst of activity around saccade

Relate the layers of the superior colliculus to the neurons involved in saccadic eye movement

``` Superficial = visual neurons Intermediate = Visual/ movement neuron Deep = movement neuron ```

Which brain area do saccade planning and generation?

Superior colliculus = planning the particular metrics (amplitude, direction)of a saccade. Frontal eye field = higher level role in target selection for saccade

Damage to one of SC or FEF causes permanent loss of saccadic eye movement. T or F?

False Lesions made to the SC alone or the FEF alone cause transient deficits with saccades, but these largely recover lesions are made to both SC and FEF = permanent loss

Frontal eye field send signals to which brain region for processing horizontal movement?

Horizontal movement –Paramedian Pontine Reticular Formation(PPRF) 2 pathways: 1) Indirect: by projections to the ipsilateral Superior Colliculus, which in turn projects to the contralateral PPRF. 2)Direct: by projections to the contralateral PPRF

Describe outflow tracts of the Paramedian Pontine Reticular Formation. (For horizontal eye movement)

1) Ipsilateral Lateral rectus (abducen) | 2) Medial longitudinal fascilulus > Contralateral oculomotor nucleus > Contralateral Medial rectus

Part of brain affected: Gaze to the right impaired.

Lesion upstream to right abducens nucleus

Part of brain affected: Impaired adduction of left eye.

Lesion in left medial longitudinal fasciculus

Part of brain affected: Impaired adduction of left eye and ptosis.

oculomotor nerve palsy (common)

Part of brain affected: Eyes cannot be moved to right. Intact left pontine center moves eyes to left

Lesion upstream to right pontine gaze center

Which brain area integrates sensory input (sound, vision)?

Angular gyrus of parietal-temporal-occipital association cortex