The Vestibular and Optokinetic Systems

2008 ◽  
Author(s):  
Agnes Wong
Keyword(s):  
Visual Information ◽  
Brain Structures ◽  
Head Movements ◽  
Head Motion ◽  
Ocular Reflex ◽  
Vestibulo Ocular Reflex ◽  
Position And Orientation ◽  
Change Position ◽  
Direction Information ◽  
Eye Velocity

The vestibulo-ocular and optokinetic reflexes are the earliest eye movements to appear phylogenetically. The vestibulo-ocular reflex (VOR) stabilizes retinal images during head motion by counter-rotating the eyes at the same speed as the head but in the opposite direction. Information about head motion passes from the vestibular sensors in the inner ear to the VOR circuitry within the brainstem, which computes an appropriate eye velocity command. The eyes, confined in their bony orbits, normally do not change position, and their motion relative to the head is restricted to a change in orientation. However, the head can both change position and orientation relative to space. Thus, the function of the VOR is to generate eye orientation that best compensates for changes in position and orientation of the head. Because the drive for this reflex is vestibular rather than visual, it operates even in darkness. To appreciate the benefits of having our eyes under vestibular and not just visual control, hold a page of text in front of you, and oscillate it back and forth horizontally at a rate of about two cycles per second. You will find that the text is blurred. However, if you hold the page still and instead oscillate your head at the same rate, you will be able to read the text clearly. This is because when the page moves, only visual information is available. Visual information normally takes about 100 msec to travel from the visual cortices, through a series of brain structures, to the ocular motoneurons that move the eyes. This delay is simply too long for the eyes to keep up with the oscillating page. However, when the head moves, both vestibular and visual information are available. Vestibular information takes only about 7–15 msec to travel from the vestibular sensors, through the brainstem, to the ocular motoneurons. With this short latency, the eyes can easily compensate for the rapid oscillation of the head. Thus, damages to the vestibular system often cause oscillopsia, an illusion of motion in the stationary environment, especially during head movements.

A review of the effects of space flight on the asymmetry of vertical optokinetic and vestibulo-ocular reflexes

2003 ◽  
Vol 13 (4-6) ◽  
pp. 255-263
Author(s):  
Gilles Clément
Keyword(s):  
Phase Velocity ◽  
Optokinetic Nystagmus ◽  
Visual Stimulation ◽  
Head Movements ◽  
Slow Phase ◽  
Eye Position ◽  
Slow Phase Velocity ◽  
Ocular Reflex ◽  
Vestibulo Ocular Reflex ◽  
Eye Velocity

Prolonged microgravity during orbital flight is a unique way to modify the otolith inputs and to determine the extent of their contribution to the vertical vestibulo-ocular reflex (VOR) and optokinetic nystagmus (OKN). This paper reviews the data collected on 10 astronauts during several space missions and focuses on the changes in the up-down asymmetry. Both the OKN elicited by vertical visual stimulation and the active VOR elicited by voluntary pitch head movements showed an asymmetry before flight, with upward slow phase velocity higher than downward slow phase velocity. Early in-flight, this asymmetry was inverted, and a symmetry of both responses was later observed. An upward shift in the vertical mean eye position in both OKN and VOR suggests that these effects may be related to otolith-dependent changes in eye position which, in themselves, affect slow phase eye velocity.

scholarly journals The Vestibulo-ocular Reflex During Active Head Motion in Chiari II Malformation

2008 ◽  
Vol 35 (4) ◽  
pp. 495-500 ◽  
Author(s):  
Michael S. Salman ◽  
James A. Sharpe ◽  
Linda Lillakas ◽  
Maureen Dennis ◽  
Martin J. Steinbach
Keyword(s):  
High Gain ◽  
Head Movements ◽  
Head Motion ◽  
Control Group ◽  
Healthy Children ◽  
Eye Tracker ◽  
Ocular Reflex ◽  
Vestibulo Ocular Reflex ◽  
Chiari Ii ◽  
Age Range

Background:Chiari type II malformation (CII) is a developmental anomaly of the cerebellum and brainstem, which are important structures for processing the vestibulo-ocular reflex (VOR). We investigated the effects of the deformity of CII on the angular VOR during active head motion.Methods:Eye and head movements were recorded using an infrared eye tracker and magnetic head tracker in 20 participants with CII [11 males, age range 8-19 years, mean (SD) 14.4 (3.2) years]. Thirty-eight age-matched healthy children and adolescents (21 males) constituted the control group. Participants were instructed to ‘look’ in darkness at the position of their thumb, placed 25 cm away, while they made horizontal and vertical sinusoidal head rotations at frequencies of about 0.5 Hz and 2 Hz. Parametric and non-parametric tests were used to compare the two groups.Results:The VOR gains, the ratio of eye to head velocities, were abnormally low in two participants with CII and abnormally high in one participant with CII.Conclusion:The majority of participants with CII had normal VOR performance in this investigation. However, the deformity of CII can impair the active angular VOR in some patients with CII. Low gain is attributed to brainstem damage and high gain to cerebellar dysfunction.

scholarly journals Normal Performance and Expression of Learning in the Vestibulo-Ocular Reflex (VOR) at High Frequencies

2005 ◽  
Vol 93 (4) ◽  
pp. 2028-2038 ◽  
Author(s):  
Ramnarayan Ramachandran ◽  
Stephen G. Lisberger
Keyword(s):  
Phase Shift ◽  
Harmonic Distortion ◽  
Head Movements ◽  
High Frequencies ◽  
Head Velocity ◽  
Ocular Reflex ◽  
Before And After ◽  
Vestibulo Ocular Reflex ◽  
Eye Velocity ◽  
Normal Performance

The rotatory vestibulo-ocular reflex (VOR) keeps the visual world stable during head movements by causing eye velocity that is equal in amplitude and opposite in direction to angular head velocity. We have studied the performance of the VOR in darkness for sinusoidal angular head oscillation at frequencies ranging from 0.5 to 50 Hz. At frequencies of ≥25 Hz, the harmonic distortion of the stimulus and response were estimated to be <14 and 22%, respectively. We measured the gain of the VOR (eye velocity divided by head velocity) and the phase shift between eye and head velocity before and after adaptation with altered vision. Before adaptation, VOR gains were close to unity for frequencies ≤20 Hz and increased as a function of frequency reaching values of 3 or 4 at 50 Hz. Eye velocity was almost perfectly out of phase with head velocity for frequencies ≤12.5 Hz, and lagged perfect compensation increasingly as a function of frequency. After adaptive modification of the VOR with magnifying or miniaturizing optics, gain showed maximal changes at frequencies <12.5 Hz, smaller changes at higher frequencies, and no change at frequencies larger than 25 Hz. Between 15 and 25 Hz, the phase of eye velocity led the unmodified VOR by as much as 50° when the gain of the VOR had been decreased, and lagged when the gain of the VOR had been increased. We were able to reproduce the main features of our data with a two-pathway model of the VOR, where the two pathways had different relationships between phase shift and frequency.

A neural network model of the vestibulo-ocular reflex using a local synaptic learning rule

1992 ◽  
Vol 337 (1281) ◽  
pp. 327-330 ◽  
Keyword(s):  
Neural Network ◽  
Learning Rule ◽  
Semicircular Canals ◽  
Head Movements ◽  
Learning Network ◽  
Ocular Reflex ◽  
Clear Vision ◽  
Vestibulo Ocular Reflex ◽  
Eye Velocity ◽  
Synaptic Learning

Vertebrates use the vestibulo-ocular reflex to maintain clear vision during head movements. This reflex requires eye-velocity com m ands from the semicircular canals to be integrated (mathematically) to produce eye-position com m ands for the extraocular muscles. This is accomplished by a neural network in the caudal pons. A model of this network is proposed using positive feedback via lateral inhibition. The model has been adapted to a learning network. We have developed a synaptic learning rule using only local information to make the model more physiological.

The vertical vestibulo-ocular reflex, and its interaction with vision during active head motion: Effects of aging

2001 ◽  
Vol 11 (1) ◽  
pp. 3-12
Author(s):  
Ji Soo Kim ◽  
James A. Sharpe
Keyword(s):  
Smooth Pursuit ◽  
Low Frequency ◽  
The Elderly ◽  
Head Motion ◽  
Head Tracking ◽  
Elderly Age ◽  
Ocular Reflex ◽  
Visual Enhancement ◽  
Vestibulo Ocular Reflex ◽  
Effects Of Aging

The effects of aging on the vertical vestibulo-ocular reflex (VOR), and its interactions with vision during active head motion had not been investigated. We measured smooth pursuit, combined eye-head tracking, the VOR, and its visual enhancement and cancellation during active head motion in pitch using a magnetic search coil technique in 21 younger (age < 65) and 10 elderly (age ⩾ 65) subjects. With the head immobile, subjects pursued a target moving sinusoidally with a frequency range of 0.125 to 2.0 Hz, and with peak target accelerations (PTAs) ranging from 12 to 789Âř/s 2 . Combined eye-head tracking, the VOR in darkness, and its visual enhancement during fixation of an earth-fixed target (VVOR) were measured during active sinusoidal head motion with a peak-to-peak amplitude of 20Âř at frequencies of 0.25, 0.5, 1.0 and 2.0 Hz. The efficacy of VOR cancellation was determined from VOR gains during combined eye-head tracking. VOR and VVOR gains were symmetrical in both directions and did not change with aging, except for reduced gains of the downward VOR and VVOR at low frequency (0.25 Hz). However, in the elderly, smooth pursuit, and combined eye-head tracking gains and the efficacy of cancellation of the VOR were significantly lower than in younger subjects. In both the young and elderly groups, VOR gain in darkness did not vary with the frequency of active head motion while the gains of smooth pursuit, combined eye-head tracking, and VVOR declined with increasing target frequency. VOR and VVOR performance in the elderly implicates relative preservation of neural structures subserving vertical vestibular smooth eye motion in senescence.

Viewing Target Distance Influences the Vestibulo-Ocular Reflex Gain when Assessed Using the Video Head Impulse Test

2018 ◽  
Vol 23 (5) ◽  
pp. 285-289 ◽  
Author(s):  
Patricia Castro ◽  
Sara Sena Esteves ◽  
Florencia Lerchundi ◽  
David Buckwell ◽  
Michael A. Gresty ◽  
...  
Keyword(s):  
Head Movements ◽  
Target Distance ◽  
Head Impulse Test ◽  
Video Head Impulse Test ◽  
Gaze Stabilization ◽  
Head Impulse ◽  
Ocular Reflex ◽  
Significant Difference ◽  
Vestibulo Ocular Reflex ◽  
Reflex Gain

Gaze stabilization during head movements is provided by the vestibulo-ocular reflex (VOR). Clinical assessment of this reflex is performed using the video Head Impulse Test (vHIT). To date, the influence of different fixation distances on VOR gain using the vHIT has not been explored. We assessed the effect of target proximity on the horizontal VOR using the vHIT. Firstly, we assessed the VOR gain in 18 healthy subjects with 5 viewing target distances (150, 40, 30, 20, and 10 cm). The gain increased significantly as the viewing target distance decreased. A second experiment on 10 subjects was performed in darkness whilst the subjects were imagining targets at different distances. There were significant inverse relationships between gain and distance for both the real and the imaginary targets. There was a statistically significant difference between light and dark gains for the 20- and 40-cm distances, but not for the 150-cm distance. Theoretical VOR gains for different target distances were calculated and compared with those found in light and darkness. The increase in gain observed for near targets was lower than predicted by geometrical calculations, implying a physiological ceiling effect on the VOR. The VOR gain in the dark, as assessed with the vHIT, demonstrates an enhancement associated with a reduced target distance.

Eye-Head Movement Coordination: Vestibulo-Ocular Reflex Suppression with Head-Fixed Target Fixation1

1991 ◽  
Vol 1 (2) ◽  
pp. 161-170
Author(s):  
Jean-Louis Vercher ◽  
Gabriel M. Gauthier
Keyword(s):  
Eye Movements ◽  
Time Course ◽  
Mental Arithmetic ◽  
Visual Space ◽  
Head Movements ◽  
Total Darkness ◽  
Fixed Target ◽  
Ocular Reflex ◽  
Optokinetic Reflex ◽  
Vestibulo Ocular Reflex

To maintain clear vision, the images on the retina must remain reasonably stable. Head movements are generally dealt with successfully by counter-rotation of the eyes induced by the combined actions of the vestibulo-ocular reflex (VOR) and the optokinetic reflex. A problem of importance relates to the value of the so-called intrinsic gain of the VOR (VORG) in man, and how this gain is modulated to provide appropriate eye movements. We have studied these problems in two situations: 1. fixation of a stationary object of the visual space while the head moves; 2. fixation of an object moving with the head. These two situations were compared to a basic condition in which no visual target was allowed in order to induce “pure” VOR. Eye movements were recorded in seated subjects during stationary sinusoidal and transient rotations around the vertical axis. Subjects were in total darkness (DARK condition) and involved in mental arithmetic. Alternatively, they were provided with a small foveal target, either fixed with respect to earth (earth-fixed target: EFT condition), or moving with them (chair-fixed-target: CFT condition). The stationary rotation experiment was used as baseline for the ensuing experiment and yielded control data in agreement with the literature. In all 3 visual conditions, typical responses to transient rotations were rigorously identical during the first 200 ms. They showed, sequentially, a 16-ms delay of the eye behind the head and a rapid increase in eye velocity during 75 to 80 ms, after which the average VORG was 0.9 ± 0.15. During the following 50 to 100 ms, the gain remained around 0.9 in all three conditions. Beyond 200 ms, the VORG remained around 0.9 in DARK and increased slowly towards 1 or decreased towards zero in the EFT and CFT conditions, respectively. The time-course of the later events suggests that visual tracking mechanisms came into play to reduce retinal slip through smooth pursuit, and position error through saccades. Our data also show that in total darkness VORG is set to 0.9 in man. Lower values reported in the literature essentially reflect predictive properties of the vestibulo-ocular mechanism, particularly evident when the input signal is a sinewave.

Modification of compensatory saccades after aVOR gain recovery

2007 ◽  
Vol 16 (6) ◽  
pp. 285-291
Author(s):  
Michael C. Schubert ◽  
Americo A. Migliaccio ◽  
Charles C. Della Santina
Keyword(s):  
Head Rotation ◽  
Rehabilitation Program ◽  
Inverse Dynamic ◽  
Gaze Stabilization ◽  
Ocular Reflex ◽  
Dynamic Relationship ◽  
Vestibulo Ocular Reflex ◽  
Functional Relevance ◽  
Vestibular Neuronitis ◽  
Eye Velocity

The recruitment of extra-vestibular mechanisms to assist a deficient angular vestibulo-ocular reflex (aVOR) during ipsilesional head rotations is well established and includes saccades of reduced latency that occur in the direction of the lesioned aVOR, termed compensatory saccades (CS). Less well known is the functional relevance of these unique saccades. Here we report a 42 y.o. male diagnosed with right unilateral vestibular hypofunction due to vestibular neuronitis who underwent a vestibular rehabilitation program including gaze stabilization exercises. After three weeks, he had a significant improvement in his ability to see clearly during head rotation. Our data show a reduction in the recruitment and magnitude of CS as well as improved peripheral aVOR gain (eye velocity/head velocity) and retinal eye velocity. Our data suggest an inverse, dynamic relationship between the recruitment of CS and the gain of the aVOR.

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