Eye Movements and Sensorimotor Integration Flashcards
If you cannot move your eyes?
Really inhibits your ability to visually perceive things
Stabilized retinal images: make sure the image always falls on exactly the same parts of the retina
Stabilized images rapidly disappear
Cannot see it anymore
Even when you are staring at a stationary image, your eyes are making slight movements, just fractions of a degree, to keep the image “fresh”
Three Antagonistic Pairs of Muscles (name them)
- Lateral and medial rectus muscles - Horizontal movements
- Superior and inferior rectus muscles (both CN III)
- Superior (trochlear, CN IV) and inferior oblique muscles (CN III)
Medial rectus:
Medial rectus: adduction (toward the nose); controlled by oculomotor nerve (CNIII)
Lateral rectus:
- direction of movement
- innervated by
abduction (away from the nose); controlled by abducens nerve (CNVI)
Superior and inferior rectus muscles
(both CN III)
*When eyes are abducted- rectus muscles are primary eye movers
Oculomotor nerve (CN III) -in addition to the muscles of the eyes... innervates
also innervates the levator muscles of the eyelid and has parasympathetic function to help control pupillary constriction (Edinger-Westphal nucleus)
-controls 4 of the eye muscles
Types of Eye Movements and Their Functions
5 basic eye movements grouped into two categories
*Those that SHIFT the direction of gaze Important for foveation Movements: vergence movements *Those that STABILIZE the gaze -Help maintain foveation while the head is moving
Movements: Vergence, saccades, smooth pursuit movements, and vestibulo-ocular and optokinetic movements
*Eye Movements that SHIFT the direction of gaze
-Important for foveation
Movements: vergence movements
*Eye movemnts that STABILIZE the gaze
*Help maintain foveation while the head is moving
Movements: saccades, smooth pursuit movements, and vestibulo-ocular and optokinetic movements
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5 movements of the eyes
Vergence Movements Saccades Smooth Pursuit Movements Vestibulo-ocular Optokinetic Eye Movements
Vergence Movements
-when required
Align the fovea of each eye with targets located at different distances
Required to track a target that is moving closer or further away
Commonly used with abruptly shifting the direction of gaze from a near object to a far object
*These movements are disconjugate/disjunctive, meaning that the eyes do not have to move in the same direction
Saccades
- voluntary and/or reflexively
- need a target (t or f)
*Can be elicited voluntarily, but also occur reflexively
*Have a target for a saccade
It moves
It takes a brief amount of time for the eyes to move to align with the target and initiate another saccade (have to set up a new motor command to move the eyes)
*If the target moves during this delay, the new saccade will miss the target and another one has to be initiated (new motor command)
see graph slide 12
Smooth Pursuit Movements
- when used?
- reflex or voluntarily?
- Slower tracking movements of the eyes
- Designed to keep a moving stimulus on the fovea once foveation has been achieved
- Under voluntary control in that you can choose to track something or not
Saccade + Smooth Pursuit
for tracking
- Saccade to foveate target (to catch up) and then smooth pursuit movements to track it (track with it, no longer require saccades)
- Smooth pursuit movements match velocity of target (Speed and target)
slide 14: Eye movements = blue
Target= red
Vestibulo-ocular and Optokinetic Eye Movements
- Work together to move the eyes and stabilize the gaze relative to the external world and compensating for head movements
- Reflexive responses
- Keep images from slipping on the surface of the retina as head position varies
Vestibulo-ocular:
-limitations
*stare at something and move your head back and forth. *Eyes automatically move to help maintain gaze
*Detects changes in head position and produces corrective eye movements
(as head moves can continue to see what you are looking at)
*Limitations: speed (insensitive to slow movements) and persistent rotations of the head
Optokinetic system:
- similar to Vestibulo-ocular, but is very sensitive to slow movements of large areas of the visual field
- Head movements slow, vestibular info declines, and optokinetic system fine with that and will prevent the image from slipping across the retina
Eye Movements: Key to Neurological Exams
(Eye movements are a super important part of neurological examinations)
-they can test or check or challenge 3 things i think)
*They test the function of several CNs (II, III, IV, VI)
*Also challenge circuits that span most of the CNS (except spinal cord mostly)
*Check voluntary and involuntary aspects of eye movement
Learn more on Page 453
Neural Control of Saccadic Movements
Moving the eyes to fixate on a target in space requires two things:
Control the amplitude (how far) of movement
Control the direction of movement
AMPLITUDE: is one of the two things required to move the eyes to fixate on a target
(Neural Control of Saccadic Movements)
encoded by duration of neuronal activity in the lower motor neurons
After each saccade, reestablish baseline activity to hold the eye steady
DIRECTION: is one of the two things required to move the eyes to fixate on a target
(Neural Control of Saccadic Movements)
- is determined by which eye muscles are activated
- Not easy to separately control each muscle independently
- Controlled by local circuit neurons in two gaze centers
Gaze Centers
- location
- name them
- Located in the reticular formation
- Paramedian pontine reticular formation (PPRF)
- Rostral interstitial nucleus/mesencephalic reticular formation
- Activation of each gaze center separately results in eye movements along that single axis
- Activation in concert results in oblique movements (not oblique muscle action, per se)
*Paramedian pontine reticular formation (PPRF):
function
- horizontal gaze center
- Collection of local circuit neurons near the midline of the pons
*Rostral interstitial nucleus/mesencephalic reticular formation:
- Rostral interstitial nucleus/mesencephalic reticular formation: vertical gaze center
- Collection of local circuit neurons in the rostral part of the midbrain reticular formation
PPRF
(horizontal gaze center)
- Works with oculomotor and abducens nuclei to generate a horizontal saccade (Example- saccade to the right)
- Neurons of the PPRF innervate neurons in the abducens nucleus on both sides of the brain
- Two types of cells: lower motor neurons (that innervate the lateral rectus muscle on same side) and internuclear neurons that send their axons across the midline
- Axons of the internuclear neurons ascend in the medial longitudinal fasciculus and terminate in the portion of the OCULOMOTOR NUCLEUS that contains lower motor neurons that control the medial rectus muscle
- Activation of PPRF neurons on the right side –> horizontal movements in both eyes to the right
- Also send axons to the medullary reticular formation
- Contact inhibitory local circuit neurons, which project to the contralateral abducens nucleus on lower motor neurons and internuclear neurons
- These connections serve to reduce activity that would move the eye in the wrong direction
Where is the sensory part of sensorimotor coming in?
(how does sensory information get incorporated***)
-main players
*Have to figure out what is a salient target and where it is in space : This comes primarily from the visual system (but not limited to this)
- Superior Colliculus (aka optic tectum in non-mammalian vertebrates):
- Assorted areas of the frontal and parietal cortices, including the FRONTAL EYE FIELDS (in frontal lobe rostral to premotor cortex)
- The sensory map is in line with the motor map
- Sensory info comes in and leads to activation of neighboring upper motor neurons that will move the eye an appropriate amount to align the fovea to the target
Both the superior colliculus and frontal eye fields have a) ____ and b) ________
Both the superior colliculus and frontal eye fields have a) upper motor neurons, and b) a topographical map of eye movement vectors
- Activation of a particular site of either leads to a saccadic eye movement in a specified direction and distance
- So, really they are trying to elicit the activation of specific movements more than a whole bunch of separate changes to eye muscles
- Saccades are about ___ coordinates, not _____ coordinates. Uses information about the location of the retinal image and current information about the position of the eyes. *Formulate a “____ code” in the ______ and that is translated into a “___ code” in the gaze centers –> direct activity of ____neurons
- Involves integration of multiple sensory modalities
Saccades are about movement coordinates, not retinotopic coordinates
Uses information about the location of the retinal image and current information about the position of the eyes
Formulate a “place code” in the superior colliculus (upper motor neurons) and that is translated into a “rate code” in the gaze centers –> direct activity of lower motor neurons
-Involves integration of multiple sensory modalities
Superior Colliculus Outputs
To PPRF (horizontal gaze center) and mesencephalic reticular formation (vertical gaze center)
Frontal Eye Fields
- -> ?
- how control eye movements?
- Frontal eye fields –> superior colliculus –> PPRF on contralateral side
- Also to the vertical gaze center, but why make this more complicated?
- So, frontal eye fields can control eye movements by activating upper motor neurons in the superior colliculus
- Frontal eye fields –> PPRF on contralateral side
- Can directly influence eye movements w/o the superior colliculus
Frontal eye fields connections:
slide 32
Directly connection to the gaze center but can involve the superior Colliculus (But sometimes do not need to)
Frontal eye fields –> PPRF on contralateral side
Can directly influence eye movements w/o the superior colliculus
Damage to frontal eye fields
problems with saccades on side contralateral to the lesion
Damage to frontal eye fields –> produce permanent deficits in ability to make saccades that are not guided by an external target
*Cannot voluntarily direct eyes away from a stimulus (anti-saccade)
Damage to superior colliculus
*saccades still occur, but they may be slower/less accurate
- Suggests the frontal eye fields and the superior colliculus compensate and complement each other
- Do NOT have the same function
Damage to superior colliculus –> permanent deficit in ability to perform express saccades
Short-latency, reflex-like eye movements that are mediated by direct pathways from retina/visual cortex –> superior colliculus
The frontal eye fields are essential for _______ to locate an _____
Different levels of activity in response to targets and distractors
Suggests that the frontal eye fields enhance the neuronal responses to stimuli that will be selected as saccade targets and also suppress the responses to UNINTERESTING/ DISTRACTING stimuli
Reduce unwanted saccades
The frontal eye fields are essential for systematic scanning to locate an OBJECT OF INTEREST within an array of distracting objects
Different levels of activity in response to targets and distractors
Suggests that the frontal eye fields enhance the neuronal responses to stimuli that will be selected as saccade targets and also suppress the responses to UNINTERESTING/ DISTRACTING stimuli
-Reduce unwanted saccades
Neural Control of Smooth Pursuit Movements
*Under control of the superior colliculus and frontal eye fields too
*Mediated by neurons in the PPRF
Exact pathways not fully understood, but probably similar to those seen for saccadic movement
Do know that neurons in the striate and extrastriate visual cortices are supplying essential sensory information
Remember- have neurons that selectively respond to motion and orientation
Neural Control of Vergence Movements
- Also not well understood
- Does require extrastriate cortex function
The extrastriate occipital cortex decides the appropriate command to converge or diverge the eyes based on the amount of binocular disparity and send that out to vergence centers in the brainstem
One center is made of local circuit neurons in the midbrain by the oculomotor nucleus
Why do we like to move our eyes?
Our area of highest visual acuity is restricted to the fovea
So, we want to be able to move our fovea around, so to speak, so we can see everything around us with as much acuity as possible
FOVEATION: the act of directing the fovea towards new objects of interest
Foveation***
Foveation: the act of directing the fovea towards new objects of interest
Saccades
Quick movements of the eye between different points of focus/interest to align the foveae
Little to no visual perception occurs during a saccade
Density of spots represent points of fixation where the person paused to take in more visual information
Vision is an active process
Even if sometimes seems stagnent
Targeted scanning to convey the most significant information from the visual scene
Neuroscience in Action: who do advertisers use “this stuff”?
Neuroscience in Action: advertisers make use of this stuff to figure out which pictures, words, and whatnot make their advertisements more effective
*Lateral and medial rectus muscles
-one of the Three Antagonistic Pairs of Muscles
*Lateral and medial rectus muscles
Horizontal movements
Superior and inferior oblique muscles
Superior (trochlear, CN IV) and inferior oblique muscles (CN III)
-one of the Three Antagonistic Pairs of Muscles
Vertical movements
Elevation due to action of superior rectus and inferior oblique
Depression due to action of the inferior rectus and superior oblique
Varies on horizontal position
When eye is adducted- oblique muscles are primary movers
Oblique muscles also responsible for torsional movements (turning)
Saccades
-need a target (t or f)
true
Eye Movements: Key to Neurological Exams- can test the function of which cranial nerves
*They test the function of several CNs (II, III, IV, VI)
in regards to the sensory part of sensorimotor
(sensory integrations)
Both the superior colliculus and frontal eye fields have (2)
Both the superior colliculus and frontal eye fields have a) upper motor neurons, and b) a topographical map of eye movement vectors
Activation of a particular site of either leads to a saccadic eye movement in a specified direction and distance
So, really they are trying to elicit the activation of specific movements more than a whole bunch of separate changes to eye muscles
*Both also contain cells that are activated by visual stimuli, but the relationship between sensory and motor output better understood for the superior colliculus
superior colliculus
in regards to the sensory part of sensorimotor
sensory integrations
- Retinal axons synapse along topographical map in superior colliculus
- Also have axons from cortical visual areas that participate in the dorsal spatial vision pathway (don’t worry about this)
*Superior colliculus also have neurons that respond to auditory and somatosensory stimuli, and their location in space
These maps are in line with the visual and motor ones
Helps you orient your gaze to a stimulus that did not originate as a visual stimulus
*This motor action is more about MOVEMENT INTENTION rather than moving the eyes to a fixed point in space
Still about vectors of direction and whatnots
T/F the Frontal Eye Fields always goes to the superior colliculus
False
-Can directly influence eye movements w/o the superior colliculus
striate neurons:
-are supplying what type of informaiton?
-important to Neural Control of Smooth Pursuit Movements
Do know that neurons in the striate and extrastriate visual cortices are supplying essential sensory information
Remember- have neurons that selectively respond to motion and orientation
Stabilized images …
rapidly disappear
*The eye movements that occur during REM sleep :
*The eye movements that occur during REM sleep are saccades
Slower tracking movements of the eyes
Smooth Pursuit Movements
T/F Most people can only make these Smooth Pursuit Movements if they have something to track
TRUE
what must occur before smooth pursuit movements can track?
foveation
*Smooth Pursuit moevements are designed to keep a moving stimulus on the fovea once foveation has been achieved
Reflexive responses of eyes: muscles used
Vestibulo-ocular and Optokinetic Eye Movements
After each saccade, must ______ to hold the eye steady
After each saccade, reestablish baseline activity to hold the eye steady
(amplitude)
Damage to this CN III
Damage to this nerve –> impairment of eye movement, drooping eyelids (ptosis), and pupillary dilation (no parasympathetic balance of constriction to sympathetic inputs to dilator muscles of the iris)
Retinal axons synapse along topographical map in ______
superior colliculus
damage to which CN leads to ptosis?
CN III
When visually examining an object such as a painting of a face, a person will usually
make many rapid eye movements, in different directions, acquiring information primarily during brief pauses at different locations on the object.
A patient is having trouble abducting their left eye (moving the eye in a direction away from the nose). What nervous system damage would you expect to find from diagnostic tests?
Damage to the left cranial nerve VI
A patient complains of inability to move his right eye toward his nose and a drooping right eyelid. What other symptom would you expect to find upon examination?
Pupillary dilation in right eye
T/F Retinal adaptation is thought to contribute to the stabilized image phenomenon.
TRUE
When shaking one’s head back and forth while looking straight ahead at a stationary object, the mechanism that maintains the focal image at a roughly constant location on the retina is called
vestibulo-ocular
patient recovering from a car accident discovers that she can no longer voluntarily direct her gaze away from a stimulus in her visual field (she cannot perform an anti-saccade). The patient most likely has sustained damage in ?
frontal eye field
T/F in the Superior Colliculus, location in visual space is mapped in register with an auditory map.
TRUE
T/F Activity in the superficial, visual layer of the SC is not necessary for a saccade to occur.
TRUE
Area MT is involved in in the generation of ____ eye movements?
smooth pursuit eye movements
