Eye Movements Flashcards

1
Q

What makes the Fovea special?

A
  • area of highest visual acuity and colour vision
  • densely/entirely packed with cones
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2
Q

Why are eye movements important?

A
  • essential for active visual perception
  • example for motor control
  • key indicators of neurological function and dysfunction
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3
Q

What are the different types of eye movements and which 2 basic functions do they serve?

A
  • shifting gaze: saccade, smooth pursuit, vergence
  • stabilizing gaze: vestibulo-ocular reflex, optokinetic reflex
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4
Q

Saccade Features

A
  • 3-5 every second
  • elicited reflexively or voluntarily
  • ballistic
  • fastest movement of the human body
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5
Q

What is Smooth Pursuit?

A
  • tracking movement to keep fovea aligned with moving stimulus
  • much slower than saccades
  • in absence of moving stimulus only after intensive training
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6
Q

What is Vergence?

A
  • disconjugate (= not paired / opposite of conjugate) eye movement to switch focus between objects that are not equally distant
  • far-to-near focus (convergence), near-to-far focus (divergence)
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7
Q

vestibulo-ocular & optokinetic reflex

A
  • operate together to stabilize gaze relative to external world
  • vestibulo-ocular reflex compensates for rapid head movements using vestibular information
  • optokinetic reflex compensates for slow, large-scale movement of visual scene using cues for visual field motion
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8
Q

What extraocular muscles are there and what are their roles?

A
  • lateral vs. medial rectus muscles (horizontal axis)
  • superior vs. inferior rectus muscles (vertical axis)
  • superior vs. inferior oblique muscles (torsional axis)
  • horizontal movements controlled by lateral and medial rectus muscles
  • vertical movements require coordination of superior and inferior rectus (elevation/depression) and oblique muscles
  • contributions depend on position on horizontal axis
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9
Q

adduction vs. abduction

A
  • adduction: movement toward nose
  • abduction: movement away from nose
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10
Q

What cranial nerves innervate which extraocular muscles?

A
  • oculomotor nerve (III) innervates ipsilateral medial rectus, superior and inferior rectus, and inferior oblique muscle (as well as levator muscle of eyelid and involved in pupillary constriction)
  • trochlear nerve (IV) innervates contralateral superior oblique muscle
  • abducens nerve (VI) innervates ipsilateral lateral rectus muscle and portion of contralateral oculomotor nucleus innervating medial rectus muscle (via medial longitudinal fasciculus)
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11
Q

How is saccade amplitude encoded?

A
  • by duration of neural activity in lower motor neurons of oculomotor nuclei
  • baseline level of discharge is correlated with position of eye in orbit
  • steady baseline level of firing generates muscle force needed to hold eye in its current position
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12
Q

How is saccade direction encoded?

A
  • determined by activated combination of eye muscles
  • specified by relative activation of 2 gaze centers in reticular formation
  • horizontal gaze center: paramedian pontine reticular formation (PPRF)
  • vertical gaze center: rostral interstitial nucleus
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13
Q

Projections from PPRF

A
  • innervates ipsilateral abducens nucleus (activation)
  • innervates inhibitory neurons in ipsilateral medullary reticular formation projecting to contralateral abducens nucleus (inhibition)
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14
Q

Which brain areas are involved in the initiation and accurate targeting of saccades?

A
  • superior colliculus
  • frontal eye field (FEF)
  • cerebellum
  • basal ganglia
  • other areas in frontal and parietal lobe
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15
Q

How are FEF and superior colliculus involved in the execution of saccades?

A
  • both project to contralateral gaze centers
  • FEF directly as well as indirectly via projections to superior colliculus
  • they provide complementary pathways, but are functionally distinct
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16
Q

How are saccades encoded in FEF and superior colliculus and how does sensorimotor integration come about?

A
  • both contain topographical map of eye movement vectors: activation of particular site elicits saccade with specific amplitude and direction
  • superior colliculus also contains sensory maps (visual, auditory, somatosensory): stimulus in space corresponds to particular site in SC
  • sensory maps are in register with motor maps: stimulus in space activates region that is generating a saccade to the stimulus
17
Q

Are saccades encoded in retinotopic coordinates?

A
  • no, encoded in movement coordinates
  • if another saccade is induced before the intended one, monkeys are still able to reach target location
  • if saccades were encoded in retinotopic coordinates, they would systematically miss target by amount of induced saccade