Ocular Motility: Lecture 9: Pursuit Eye Movements

Question 1

Overview of Pursuit

1. Continuous Slow Conjugate Eye Movements that have Velocities under what?
2. Only Animals with FOVEAE make what?
3. The Goal of the Pursuit System is to match what?

Answer 1

1. Under 70 deg/sec
2. SMOOTH PURSUIT EYE MOVEMENTS
3. the Eye Velocity to Target Velocity as close as possible

Question 2

Overview of Pursuit

1. In Adult humans, what speed can the Angular Velocity of the Head reach?
   a. How do we compensate for this?
2. During head tracking of an object, what can happen?

Answer 2

1. 200-300 deg/sec
   a. with Nulling Pursuits or by Switching off the VOR
2. Fixation would be disrupted by a counter-roll of the eyes stimulated by the Vestibulo Ocular Reflexes. Stabilization reflexes are shut off or pursuits could overcome them and keep the eyes in their primary position while following a moving target with the head.

Question 3

Overview of Pursuit

1. Most universal function of pursuit is to suppress or null what 2 things when tracking a moving target?
2. During smooth tracking of a target that moves in the same direction as the head, Smooth pursuit does what?
   a. Otherwise, what happens?

Answer 3

1. VOR or OKN
2. Cancels the VOR
   a. the VOR would move the eyes opposite the direction of the intended gaze.

Question 4

Overview of Pursuit

1. Position Error in Smooth Tracking results in either 1 of 2 things?
2. Works Best with what?
   a. Speed?

Answer 4

1. in Either a LEAD or LAG of the eye w/respect to target and is corrected by a saccade
2. with a SLOW TARGET MOVEMENTS
   a. w/a Velocity of 20-50 degrees per second.

Question 5

1. If Positional Displacement were the PRIMARY FACTOR, the Initial Movement of the Eye would be what?
2. However, if a target that’s initially centered on a screen, then at some random time, it instantaneously stepped or “jumped” a few degrees, then the response would be what?

Answer 5

1. a SACCADE DIRECTED TOWARD the TARGET
2. a SMOOTH MOVEMENT DIRECTED AWAY from the Target.
   * The INitial movement was dictated by the motion, not position, of the target.
   * The subject initially smoothly pursued the moving Eccentric Target to MATCH EYE VELOCITY to TARGET VELOCITY; this smooth pursuit was followed by longer latency foveating saccade

Question 6

Pursuit Dynamics

1. Pursuit System is AKA?
   a. Responds to CHANGE w/in what?
2. Initial 100msec pre-saccadic Pursuit is what?
   a. The Initial 20-40 msec is what?

Answer 6

1. CONTINUOUS CONTROL SYSTEM
   a. w/in one LATENCY PERIOD
2. is OPEN-LOOP
   a. is INDEPENDENT of TARGET STIMULUS Characteristics

Question 7

Pursuit Dynamics

1. The Latter 60 msec period is what?
2. the Pursuit system has a latency of how long?
   a. It is Slightly longer for what?
   b. About 50 msec of this is LOST to what?
   c. 25 msec is lost for what?
   d. the Remaining 30-80 msec is due to what?

Answer 7

1. Loosely related to Target Velocity and Eccentricity
2. 100 msec
   a. for Slow Target Velocities
   b. to Conduction in the Afferent Pathways
   c. in the Efferent Pathways
   d. due to Compensation

Question 8

Pursuit Dynamics

1. Pursuit phase has 2 General Phases: What are they?
2. Open loop means what?
3. What happens during the Closed loop state?

Answer 8

1. Open loop and Closed Loop
2. Response is ONLY influenced by the INITIAL VIEW of the target and NOT by changes in the Retinal image produced by the eye movement
3. The Eye is Responding to Alterations of the Retinal image produced by the Eye Movement response

Question 9

Pursuit Dynamics

1. The target may be moving at what speed?
   a. The eye may be moving at what speed?
   b. The resulting retinal Error, or Slip Velocity, is what?

c. The Response Velocity Keeps increasing to REDUCE what?
d. This influence of Eye Motion on the Stimulus is Called what?

Answer 9

1. 10 deg/sec
   a. 9 deg/sec
   b. 1 deg/sec
   c. REDUCE the remaining Error
   d. the Negative Feedback

Question 10

Open Loop Response

1. How long does the Early component last for?
   a. What happens during this time?
   b. Typical Values are what?
2. What begins a Movement?
3. The Late component lasts for how long?
   a. What happens during this time?
   b.

Answer 10

1. 20 msec
   a. Rapid Acceleration of the Eye that’s INDEPENDENT of the Stimulus Velocity and Retinal Image Position

b. 40-100 deg/sec
2. Initial Shrug by the Oculomotor System

3. 80 msec
   a. Velocity of the Pursuit it Modified to Conform to the INITIAL VELOCITY of the Stimulus, as well as retinal image position or distance from the Fovea

Question 11

Closed Loop Response

1. Pursuit Velocity INCREASES to REDUCE what 2 things?
2. After the INITIAL Open Loop Response, the PURSUIT RESPONSE is a REFINEMENT of the Initial ESTIMATES based on the Remaining Velocity ERRORS b/w TARGET Motion and EYE MOTION. What is this called?

Answer 11

1. Fixation Errors and Velocity Errors

2. CLOSED LOOP

Question 12

Gain of the Pursuit System (1)

1. The Eye can Speed up to Reduce a Position error or lag or increase its velocity to match that of the stimulus. What else can it do?
2. Closed Loop Pursuit Gain: What is it generally?
   a. What does this indicate?
3. Gain: Eye Velocity/Target Velocity: What is the Ideal RATIO?
4. What is the VALUE for OPEN LOOP GAIN?

Answer 12

1. It can reverse direction from Left to Right if the stimulus Reverses Direction
2. 0.90 to 0.95
   a. Indicates a HIGH DEGREE of ACCURACY for target velocities up to 30-40 deg/sec
3. 1.0
4. 20

Question 13

Gain of Pursuit System (2)

1. Gain may be reduced w/the ADDITION of what 2 things?
2. Gain REDUCES with Increased Target Amplitude over what range?
3. Vertical Pursuit has what?

Answer 13

1. of a Stationary or a Moving Background
2. 5-20 Degrees
3. Has a Lower Gain, Greater Phase Lag, Larger Error correcting saccades than horizontal pursuit

Question 14

Effects of Aging on the Pursuit System

1. Reduced DUAL MODE CLOSED LOOP GAIN
   a. What is the Avg reduction?
   b. When does it become PROGRESSIVELY WORSE?
   c. What 2 things does it do?
2. INCREASED VELOCITY LATENCY
   a. What is it?
   b. What 2 things occur?

Answer 14

1. a. 25%
   b. with increasingly Higher Target Velocities
   c. INCREASED OVERALL SACCADE FREQUENCY and REDUCED INITIAL ACCELERATION (initial acceleration is reduced by about 30%)
2. a. Overall Age-related Increases in Reaction time
   b. INCREASED DISTRACTIBILITY, and INCREASED SQUARE WAVE JERKS (defect of decreased inhibition of pause cells)

Question 15

Prediction

1. It denotes a Pattern of Target Motion that’s so constrained so that one obtains a lot of info from what?
2. Latency for pursuits due to NEURAL TRANSMISSION TIME and COMPUTATION during tracking and use of NEGATIVE FEEDBACK could make it difficult to follow a target when its path of motion has changed. The PURSUIT RESPONSE can COMPENSATE for these DELAYS by predicting what?

Answer 15

1. from PAST target movement that permits highly likely guesses about its future behavior
2. the future course of motion of redundant target motion

Question 16

Prediction (2)

1. With a Predictable stimulus, ANY observer learns to predict and TRACT what?
2. With this input, the eye can track the target to about what before GAIN REDUCES and LAG INCREASES?
   a. In contrast, with a Nonpredictable input, Response attenuation w/considerable lag present is the RULE, since such a target is what?

Answer 16

1. the Target accurately
2. 1 Hz
3. Difficult to follow due to lack of Predictability

Question 17

Prediction: Overall Improvement in Tracking Performance

1. With a Nonpredictable Input, in addition to Overall reduction in the PURSUIT COMPONENT, what occurs?

Answer 17

1. an INCREASE in SACCADIC COMPONENT (catch up or corrective saccades) to correct for the resultant Dynamically Accumulative Position Error

Question 18

1. Where does the pursuit command occur?
2. Where does Retinal Velocity Error occur?
3. What does Efferent Pathways do?

Answer 18

1. B/w Efferent pathway and the Final Motor Pathway
2. After Afferent Pathways
3. Sends + Feedback on Eye Velocity to the Reconstructed Target Velocity and affects Pursuit Command

Question 19

Horizontal Pursuit (1)

1. Where does Smooth Pursuit pathway start in PRIMATES?
   a. Signals are relayed thru what?
2. Signals from MT are relayed to what?

Answer 19

1. M Ganglion Cells in the Retina
   a. Magnocellular layers of LGN to Striate Cortex (V1) –> V2 and V3 –> MT (V5)
2. MST –> Visual Motor Area: Frontal (Smooth Pursuit subregion of Frontal Eye Field) and Posterior Parietal Cortex

Question 20

Horizontal Pursuit (2)

1. In V1, the info about motion is transferred by Neurons that Respond to what?
   a. These Signals are Further elaborated in MT, where FIRING PATTERN of the NEURONS there ENCODES what 2 things?
   b. Info about MOTION from MT is then Extracted from what?
   c. BOTH MT and MST, as well as the FRONTAL EYE FIELD, PROJECT DIRECTLY to what?
   d. This then projects to what?

Answer 20

1. to specific directions of Motion
   a. ENCODES the SPEED and DIRECTION of MOTION
   b. in the MST
   c. to the DORSOLATERAL PONTINE NUCLEI (DLPN) (in Ipsilateral Basal Pons)
   d. to the CONTRALATERAL FLOCCULUS/VENTRAL PARAFLOCCULUS and the DORSAL VERMIS in the CEREBELLUM

Question 21

Horizontal Pursuit (3)

1. The Flocculus and Fastigial Nucleus Project to what?
   a. This then projects to what?
   b. What does this Innervate?
   c. This constitutes a Double Decussation of what?

Answer 21

1. to the MEDIAL VESTIBULAR NUCLEUS (MVN) in the BRAINSTEM
   a. to the CONTRALATERAL ABDUCENS NUCLEUS
   b. the LATERAL RECTUS on the SAME SIDE and the CONTRALATERAL MEDIAL RECTUS
   c. of the Horizontal Pursuit Pathway

Question 22

Horizontal Pursuit (4)

1. The First Decussation is where?
2. The second Decussation is where?
3. in addition, the NOT receives Projections from what 2 things? Then projects to what?

Answer 22

1. PONTOCEREBELLAR PROJECTIONS from the DLPN thru Contralateral Middle Cerebellar Peduncle, to the Contralateral Flocculus/Ventral Paraflocculus and the Dorsal Vermis
2. from 2nd order Vestibular Neurons in the MVN to the CONTRALATERAL ABDUCENS NUCLEUS
3. from MT and MST; Projects to the DLPN

Question 23

Overview of projection and to what?

1. Retina
2. LGN
3. V1,V2,V3
4. FEFsem SEF to DLPN
5. V1: Causes what?
6. MT does what?

Answer 23

1. M-Ganglion Cells
2. Magnocellular
3. Striate Cortex
4. Pos Parietal Cortex
5. Direction of MOTION
6. Speed and Direction

Question 24

Vertical Pursuit (1)

1. Follows the same pathway as horizontal, EXCEPT it involves what other structure?
   a. This structure receives input from what 3 things?
   b. It then projects to what?

Answer 24

1. the ROSTRAL NUCLEUS RETICULARIS TEGMENTI PONTIS in the BASAL PONS (in place of the DLPN in horizontal)
   a. MT, MST, and Pursuit subregion of the Frontal Eye Field
   b. to the CONTRALATERAL CEREBELLUM

Question 25

Vertical Pursuit (2)

1. Omnipause Neurons in the Nucleus Raphe Interpositus, which INHIBIT what?
   a. What do they do?
2. Nucleus Prepositus Hypoglossi-MVN Complex and INC Perform INTEGRATION for what 2 things?
   a. How?

Answer 25

1. Excitatory Burst Neurons for Saccades during Fixation and Stop firing During Saccades.
   a. They Exert INHIBITORY CONTROL OVER PURSUIT
2. For Conjugate Horizontal and Vertical Pursuit respectively.
   a. By Transforming Eye Velocity Signals to Eye Position Signals

Question 26

Abnormal Pursuit (1)

1. Lesion in V1 or MT causes what?
   a. Where?
2. Lesion in MST causes what?
3. Lesion in the FEFsem, DLPM, or NOT causes what?

Answer 26

1. SCOTOMA of Motion (impaired horizontal pursuit in BOTH DIRECTIONS)
   a. in the AFFECTED CONTRALATERAL HEMIFIELD
2. Directional Pursuit Deficit (Impaired horizontal pursuit toward the side of lesion, regardless of the hemifield where the target lies)
3. Deficits in Horizontal Pursuit

Question 27

Abnormal Pursuit (2)

1. BILATERAL LESIONS of the FLOCCULUS?
2. UNILATERAL LESION of the VPF?
3. BILATERAL LESION of the FLOCCULUS and VPF?
4. Lesion in the ROSTRAL NRTP causes what?

Answer 27

1. No effect on Pursuit
2. Mild Deficit in Horizontal and Vertical Pursuit (both directions) and VOR Cancellation
3. Severe Deficit in Horizontal and Vertical Pursuit (both directions) and VOR Cancellation. Thus, VPF is the Primary structure involved in pursuit and VOR cancellation
4. Deficits in UPWARD PURSUIT

Question 28

1. Unilateral Lesion in Primary Visual Cortex?
2. Middle Temporal Area?
3. Middle Superiotemporal Area
4. Posterioparietal Cortex
5. Frontal Eye Fields: Bilateral Lesions?
6. Dorsolateral Pontine Nucleus
7. Cerebellum

Answer 28

1. Contralateral Defect
2. Scotoma specific only for VISUAL MOTION
3. Unilateral Lesion produces an Ipsilateral Defect
4. Ipsilateral Defect
5. Bilateral Defect; Unilateral = Ipsilateral Defect
6. Ipsilateral Defect
7. Lesion in Flocculus or Paraflocculus cause a serious defect of PURSUIT GAIN

Lesion in Vermis causes a MODEST DEFECT of PURSUIT GAIN

Total Cerebellectomy ABOLISHES all Pursuit

Question 29

Clinical Testing of Smooth Pursuit

1. Track a small target w/the head still.
   a. When the Gain is LOW, what happens?
   b. When the Gain is HIGH, what happens?
2. Handheld Optokinetic Drum: What is it?

Answer 29

1. a. CATCHUP SACCADES are seen, giving appearance of Saccadic Pursuit
   b. BACKUP SACCADES are seen
2. Rotating drum in front of the patient in both Horizontal and Vertical Directions: Direction and Nature of slow phases are analysed

Question 30

Clinical Testing of Smooth Pursuit

1. Pursuit ASYMMETRY: seen in peeps with what disease?
2. Pursuit REVERSAL
   a. What is it?
   b. Seen in patients with what SYNDROME?

Answer 30

1. Cerebral Hemispheric Disease
   a. Ex: Pt: Left Post. Cerebral Lesion can show fewer corrective quick phases when the drum is rotated to their left, due to low pursuit gain to the left
2. a. Corrective quick phase that beat toward the same direction as the drum rotation
   b. with Infantile Nystagmus Syndrome

Question 31

Clinical Testing of Smooth Pursuit (3)

1. Smooth pursuit function can be INFERRED by testing what?
   a. How do you do that?

Answer 31

1. VOR Cancellation

a. Spin the patient in a swivel chair