Horizontal Vestibuloocular Reflex Evoked by High-Acceleration Rotations in the Squirrel Monkey. IV. Responses After Spectacle-Induced Adaptation

2001 ◽  
Vol 86 (4) ◽  
pp. 1594-1611 ◽  
Author(s):  
Richard A. Clendaniel ◽  
David M. Lasker ◽  
Lloyd B. Minor
Keyword(s):  
Linear Term ◽  
Linear Component ◽  
Vestibuloocular Reflex ◽  
Gain Enhancement ◽  
High Acceleration ◽  
Normal Behavior ◽  
Adaptive Processes ◽  
Vor Adaptation ◽  
Differential Increase ◽  
Sinusoidal Rotations

The horizontal angular vestibuloocular reflex (VOR) evoked by sinusoidal rotations from 0.5 to 15 Hz and acceleration steps up to 3,000°/s2 to 150°/s was studied in six squirrel monkeys following adaptation with ×2.2 magnifying and ×0.45 minimizing spectacles. For sinusoidal rotations with peak velocities of 20°/s, there were significant changes in gain at all frequencies; however, the greatest gain changes occurred at the lower frequencies. The frequency- and velocity-dependent gain enhancement seen in normal monkeys was accentuated following adaptation to magnifying spectacles and diminished with adaptation to minimizing spectacles. A differential increase in gain for the steps of acceleration was noted after adaptation to the magnifying spectacles. The gain during the acceleration portion, G A, of a step of acceleration (3,000°/s2 to 150°/s) increased from preadaptation values of 1.05 ± 0.08 to 1.96 ± 0.16, while the gain during the velocity plateau, G V, only increased from 0.93 ± 0.04 to 1.36 ± 0.08. Polynomial fits to the trajectory of the response during the acceleration step revealed a greater increase in the cubic than the linear term following adaptation with the magnifying lenses. Following adaptation to the minimizing lenses, the value of G A decreased to 0.61 ± 0.08, and the value of G V decreased to 0.59 ± 0.09 for the 3,000°/s2 steps of acceleration. Polynomial fits to the trajectory of the response during the acceleration step revealed that there was a significantly greater reduction in the cubic term than in the linear term following adaptation with the minimizing lenses. These findings indicate that there is greater modification of the nonlinear as compared with the linear component of the VOR with spectacle-induced adaptation. In addition, the latency to the onset of the adapted response varied with the dynamics of the stimulus. The findings were modeled with a bilateral model of the VOR containing linear and nonlinear pathways that describe the normal behavior and adaptive processes. Adaptation for the linear pathway is described by a transfer function that shows the dependence of adaptation on the frequency of the head movement. The adaptive process for the nonlinear pathway is a gain enhancement element that provides for the accentuated gain with rising head velocity and the increased cubic component of the responses to steps of acceleration. While this model is substantially different from earlier models of VOR adaptation, it accounts for the data in the present experiments and also predicts the findings observed in the earlier studies.

Differential Adaptation of the Linear and Nonlinear Components of the Horizontal Vestibuloocular Reflex in Squirrel Monkeys

2002 ◽  
Vol 88 (6) ◽  
pp. 3534-3540 ◽  
Author(s):  
Richard A. Clendaniel ◽  
David M. Lasker ◽  
Lloyd B. Minor
Keyword(s):  
Squirrel Monkeys ◽  
Linear Component ◽  
Vestibuloocular Reflex ◽  
Nonlinear Component ◽  
Adaptive Process ◽  
Gain Enhancement ◽  
High Acceleration ◽  
Differential Adaptation ◽  
Linear And Nonlinear ◽  
Nonlinear Components

Previous work in squirrel monkeys has demonstrated the presence of linear and nonlinear components to the horizontal vestibuloocular reflex (VOR) evoked by high-acceleration rotations. The nonlinear component is seen as a rise in gain with increasing velocity of rotation at frequencies more than 2 Hz (a velocity-dependent gain enhancement). We have shown that there are greater changes in the nonlinear than linear component of the response after spectacle-induced adaptation. The present study was conducted to determine if the two components of the response share a common adaptive process. The gain of the VOR, in the dark, to sinusoidal stimuli at 4 Hz (peak velocities: 20–150°/s) and 10 Hz (peak velocities: 20 and 100°/s) was measured pre- and postadaptation. Adaptation was induced over 4 h with ×0.45 minimizing spectacles. Sum-of-sines stimuli were used to induce adaptation, and the parameters of the stimuli were adjusted to invoke only the linear or both linear and nonlinear components of the response. Preadaptation, there was a velocity-dependent gain enhancement at 4 and 10 Hz. In postadaptation with the paradigms that only recruited the linear component, there was a decrease in gain and a persistent velocity-dependent gain enhancement (indicating adaptation of only the linear component). After adaptation with the paradigm designed to recruit both the linear and nonlinear components, there was a decrease in gain and no velocity-dependent gain enhancement (indicating adaptation of both components). There were comparable changes in the response to steps of acceleration. We interpret these results to indicate that separate processes drive the adaptation of the linear and nonlinear components of the response.

Horizontal Vestibuloocular Reflex Evoked by High-Acceleration Rotations in the Squirrel Monkey. II. Responses After Canal Plugging

1999 ◽  
Vol 82 (3) ◽  
pp. 1271-1285 ◽  
Author(s):  
David M. Lasker ◽  
Douglas D. Backous ◽  
Anna Lysakowski ◽  
Griffin L. Davis ◽  
Lloyd B. Minor
Keyword(s):  
High Frequency ◽  
Peak Velocity ◽  
Vestibular Function ◽  
Semicircular Canals ◽  
Vestibuloocular Reflex ◽  
Half Cycle ◽  
High Acceleration ◽  
Linear And Nonlinear ◽  
Residual Response ◽  
Sinusoidal Rotations

The horizontal angular vestibuloocular reflex (VOR) evoked by high-frequency, high-acceleration rotations was studied in four squirrel monkeys after unilateral plugging of the three semicircular canals. During the period (1–4 days) that animals were kept in darkness after plugging, the gain during steps of acceleration (3,000°/s2, peak velocity = 150°/s) was 0.61 ± 0.14 (mean ± SD) for contralesional rotations and 0.33 ± 0.03 for ipsilesional rotations. Within 18–24 h after animals were returned to light, the VOR gain for contralesional rotations increased to 0.88 ± 0.05, whereas there was only a slight increase in the gain for ipsilesional rotations to 0.37 ± 0.07. A symmetrical increase in the gain measured at the plateau of head velocity was noted after animals were returned to light. The latency of the VOR was 8.2 ± 0.4 ms for ipsilesional and 7.1 ± 0.3 ms for contralesional rotations. The VOR evoked by sinusoidal rotations of 0.5–15 Hz, ±20°/s had no significant half-cycle asymmetries. The recovery of gain for these responses after plugging was greater at lower than at higher frequencies. Responses to rotations at higher velocities for frequencies ≥4 Hz showed an increase in contralesional half-cycle gain, whereas ipsilesional half-cycle gain was unchanged. A residual response that appeared to be canal and not otolith mediated was noted after plugging of all six semicircular canals. This response increased with frequency to reach a gain of 0.23 ± 0.03 at 15 Hz, resembling that predicted based on a reduction of the dominant time constant of the canal to 32 ms after plugging. A model incorporating linear and nonlinear pathways was used to simulate the data. The coefficients of this model were determined from data in animals with intact vestibular function. Selective increases in the gain for the linear and nonlinear pathways predicted the changes in recovery observed after canal plugging. An increase in gain of the linear pathway accounted for the recovery in VOR gain for both responses at the velocity plateau of the steps of acceleration and for the sinusoidal rotations at lower peak velocities. The increase in gain for contralesional responses to steps of acceleration and sinusoidal rotations at higher frequencies and velocities was due to an increase in the gain of the nonlinear pathway. This pathway was driven into inhibitory cutoff at low velocities and therefore made no contribution for rotations toward the ipsilesional side.

Horizontal Vestibuloocular Reflex Evoked by High-Acceleration Rotations in the Squirrel Monkey. III. Responses After Labyrinthectomy

2000 ◽  
Vol 83 (5) ◽  
pp. 2482-2496 ◽  
Author(s):  
David M. Lasker ◽  
Timothy E. Hullar ◽  
Lloyd B. Minor
Keyword(s):  
Squirrel Monkey ◽  
High Frequency ◽  
Squirrel Monkeys ◽  
Spontaneous Nystagmus ◽  
Vestibuloocular Reflex ◽  
Testing Session ◽  
High Acceleration ◽  
Unilateral Labyrinthectomy ◽  
Linear And Nonlinear ◽  
Sinusoidal Rotations

The horizontal angular vestibuloocular reflex (VOR) evoked by high-frequency, high-acceleration rotations was studied in four squirrel monkeys after unilateral labyrinthectomy. Spontaneous nystagmus was measured at the beginning and end of each testing session. During the period that animals were kept in darkness (4 days), the nystagmus at each of these times measured ∼20°/s. Within 18–24 h after return to the light, the nystagmus (measured in darkness) decreased to 2.8 ± 1.5°/s (mean ± SD) when recorded at the beginning but was 20.3 ± 3.9°/s at the end of the testing session. The latency of the VOR measured from responses to steps of acceleration (3,000°/s2 reaching a velocity of 150°/s) was 8.4 ± 0.3 ms for responses to ipsilesional rotations and 7.7 ± 0.4 ms for contralesional rotations. During the period that animals were kept in darkness after the labyrinthectomy, the gain of the VOR measured during the steps of acceleration was 0.67 ± 0.12 for contralesional rotations and 0.39 ± 0.04 for ipsilesional rotations. Within 18–24 h after return to light, the VOR gain for contralesional rotations increased to 0.87 ± 0.08, whereas there was only a slight increase for ipsilesional rotations to 0.41 ± 0.06. A symmetrical increase in the gain measured at the plateau of head velocity was noted after the animals were returned to light. The VOR evoked by sinusoidal rotations of 2–15 Hz, ±20°/s, showed a better recovery of gain at lower (2–4 Hz) than at higher (6–15 Hz) frequencies. At 0.5 Hz, gain decreased symmetrically when the peak amplitude was increased from 20 to 100°/s. At 10 Hz, gain was decreased for ipsilesional half-cycles and increased for contralesional half-cycles when velocity was raised from 20 to 50°/s. A model incorporating linear and nonlinear pathways was used to simulate the data. Selective increases in the gain for the linear pathway accounted for the recovery in VOR gain for responses at the velocity plateau of the steps of acceleration and for the sinusoidal rotations at lower peak velocities. The increase in gain for contralesional responses to steps of acceleration and sinusoidal rotations at higher frequencies and velocities was due to an increase in the contribution of the nonlinear pathway. This pathway was driven into cutoff and therefore did not affect responses for rotations toward the lesioned side.

Horizontal Vestibuloocular Reflex Evoked by High-Acceleration Rotations in the Squirrel Monkey. I. Normal Responses

1999 ◽  
Vol 82 (3) ◽  
pp. 1254-1270 ◽  
Author(s):  
Lloyd B. Minor ◽  
David M. Lasker ◽  
Douglas D. Backous ◽  
Timothy E. Hullar
Keyword(s):  
High Frequency ◽  
Polynomial Regression ◽  
Vestibular Function ◽  
Phase Lag ◽  
Vestibuloocular Reflex ◽  
Head Velocity ◽  
High Acceleration ◽  
Linear Fit ◽  
Experimental Findings ◽  
Sinusoidal Rotations

The horizontal angular vestibuloocular reflex (VOR) evoked by high-frequency, high-acceleration rotations was studied in five squirrel monkeys with intact vestibular function. The VOR evoked by steps of acceleration in darkness (3,000°/s2 reaching a velocity of 150°/s) began after a latency of 7.3 ± 1.5 ms (mean ± SD). Gain of the reflex during the acceleration was 14.2 ± 5.2% greater than that measured once the plateau head velocity had been reached. A polynomial regression was used to analyze the trajectory of the responses to steps of acceleration. A better representation of the data was obtained from a polynomial that included a cubic term in contrast to an exclusively linear fit. For sinusoidal rotations of 0.5–15 Hz with a peak velocity of 20°/s, the VOR gain measured 0.83 ± 0.06 and did not vary across frequencies or animals. The phase of these responses was close to compensatory except at 15 Hz where a lag of 5.0 ± 0.9° was noted. The VOR gain did not vary with head velocity at 0.5 Hz but increased with velocity for rotations at frequencies of ≥4 Hz (0.85 ± 0.04 at 4 Hz, 20°/s; 1.01 ± 0.05 at 100°/s, P < 0.0001). No responses to these rotations were noted in two animals that had undergone bilateral labyrinthectomy indicating that inertia of the eye had a negligible effect for these stimuli. We developed a mathematical model of VOR dynamics to account for these findings. The inputs to the reflex come from linear and nonlinear pathways. The linear pathway is responsible for the constant gain across frequencies at peak head velocity of 20°/s and also for the phase lag at higher frequencies being less than that expected based on the reflex delay. The frequency- and velocity-dependent nonlinearity in VOR gain is accounted for by the dynamics of the nonlinear pathway. A transfer function that increases the gain of this pathway with frequency and a term related to the third power of head velocity are used to represent the dynamics of this pathway. This model accounts for the experimental findings and provides a method for interpreting responses to these stimuli after vestibular lesions.

scholarly journals Angular vestibuloocular reflex responses in Otop1 mice. I. Otolith sensor input is essential for gravity context-specific adaptation

2019 ◽  
Vol 121 (6) ◽  
pp. 2291-2299 ◽  
Author(s):  
Serajul I. Khan ◽  
Charles C. Della Santina ◽  
Americo A. Migliaccio
Keyword(s):  
Semicircular Canals ◽  
Vertical Axis ◽  
Neural Circuitry ◽  
Vestibuloocular Reflex ◽  
Training Context ◽  
Specific Adaptation ◽  
Axis Parallel ◽  
Vor Adaptation ◽  
Context Specific

The role of the otoliths in mammals in the angular vestibuloocular reflex (VOR) has been difficult to determine because there is no surgical technique that can reliably ablate them without damaging the semicircular canals. The Otopetrin1 (Otop1) mouse lacks functioning otoliths because of failure to develop otoconia but seems to have otherwise normal peripheral anatomy and neural circuitry. By using these animals we sought to determine the role of the otoliths in angular VOR baseline function and adaptation. In six Otop1 mice and six control littermates we measured baseline ocular countertilt about the three primary axes in head coordinates; baseline horizontal (rotation about an Earth-vertical axis parallel to the dorsal-ventral axis) and vertical (rotation about an Earth-vertical axis parallel to the interaural axis) sinusoidal (0.2–10 Hz, 20–100°/s) VOR gain (= eye/head velocity); and the horizontal and vertical VOR after gain-increase (1.5×) and gain-decrease (0.5×) adaptation training. Countertilt responses were significantly reduced in Otop1 mice. Baseline horizontal and vertical VOR gains were similar between mouse types, and so was horizontal VOR adaptation. For control mice, vertical VOR adaptation was evident when the testing context, left ear down (LED) or right ear down (RED), was the same as the training context (LED or RED). For Otop1 mice, VOR adaptation was evident regardless of context. Our results suggest that the otolith translational signal does not contribute to the baseline angular VOR, probably because the mouse VOR is highly compensatory, and does not alter the magnitude of adaptation. However, we show that the otoliths are important for gravity context-specific angular VOR adaptation. NEW & NOTEWORTHY This is the first study examining the role of the otoliths (defined here as the utricle and saccule) in adaptation of the angular vestibuloocular reflex (VOR) in an animal model in which the otoliths are reliably inactivated and the semicircular canals preserved. We show that they do not contribute to adaptation of the normal angular VOR. However, the otoliths provide the main cue for gravity context-specific VOR adaptation.

Effect of Adaptation to Telescopic Spectacles on the Initial Human Horizontal Vestibuloocular Reflex

2000 ◽  
Vol 83 (1) ◽  
pp. 38-49 ◽  
Author(s):  
Benjamin T. Crane ◽  
Joseph L. Demer
Keyword(s):  
Head Rotation ◽  
Head Movements ◽  
Target Distance ◽  
Whole Body ◽  
Rotational Axis ◽  
Vestibuloocular Reflex ◽  
Head Acceleration ◽  
Gain Enhancement ◽  
Lower Head ◽  
Distant Target

Gain of the vestibuloocular reflex (VOR) not only varies with target distance and rotational axis, but can be chronically modified in response to prolonged wearing of head-mounted magnifiers. This study examined the effect of adaptation to telescopic spectacles on the variation of the VOR with changes in target distance and yaw rotational axis for head velocity transients having peak accelerations of 2,800 and 1,000°/s2. Eye and head movements were recorded with search coils in 10 subjects who underwent whole body rotations around vertical axes that were 10 cm anterior to the eyes, centered between the eyes, between the otoliths, or 20 cm posterior to the eyes. Immediately before each rotation, subjects viewed a target 15 or 500 cm distant. Lighting was extinguished immediately before and was restored after completion of each rotation. After initial rotations, subjects wore 1.9× magnification binocular telescopic spectacles during their daily activities for at least 6 h. Test spectacles were removed and measurement rotations were repeated. Of the eight subjects tolerant of adaptation to the telescopes, six demonstrated VOR gain enhancement after adaptation, while gain in two subjects was not increased. For all subjects, the earliest VOR began 7–10 ms after onset of head rotation regardless of axis eccentricity or target distance. Regardless of adaptation, VOR gain for the proximate target exceeded that for the distant target beginning at 20 ms after onset of head rotation. Adaptation increased VOR gain as measured 90–100 ms after head rotation onset by an average of 0.12 ± 0.02 (SE) for the higher head acceleration and 0.19 ± 0.02 for the lower head acceleration. After adaptation, four subjects exhibited significant increases in the canal VOR gain only, whereas two subjects exhibited significant increases in both angular and linear VOR gains. The latencies of linear and early angular target distance effects on VOR gain were unaffected by adaptation. The earliest significant change in angular VOR gain in response to adaptation occurred 50 and 68 ms after onset of the 2,800 and 1,000°/s2 peak head accelerations, respectively. The latency of the adaptive increase in linear VOR gain was ∼50 ms for the peak head acceleration of 2,800°/s2, and 100 ms for the peak head acceleration of 1,000°/s2. Thus VOR gain changes and latency were consistent with modification in the angular VOR in most subjects, and additionally in the linear VOR in a minority of subjects.

Cerebellar Disease Alters the Axis of the High-Acceleration Vestibuloocular Reflex

2005 ◽  
Vol 94 (5) ◽  
pp. 3417-3429 ◽  
Author(s):  
Mark F. Walker ◽  
David S. Zee
Keyword(s):  
Head Rotation ◽  
Normal Subjects ◽  
Vestibuloocular Reflex ◽  
Cerebellar Disease ◽  
Characteristic Finding ◽  
High Acceleration ◽  
The Difference ◽  
Head Impulses ◽  
Cross Axis ◽  
Eye Velocity

L. W. Schultheis and D. A. Robinson showed that the axis of the rotational vestibuloocular reflex (RVOR) cannot be altered by visual-vestibular mismatch (“cross-axis adaptation”) when the vestibulocerebellum is lesioned. This suggests that the cerebellum may calibrate the axis of eye velocity of the RVOR under natural conditions. Thus we asked whether patients with cerebellar disease have alterations in the RVOR axis and, if so, what might be the mechanism. We used three-axis scleral coils to record head and eye movements during yaw, pitch, and roll head impulses in 18 patients with cerebellar disease and in a comparison group of eight subjects without neurologic disease. We found distinct shifts of the eye-velocity axis in patients. The characteristic finding was a disconjugate upward eye velocity during yaw. Measured at 70 ms after the onset of head rotation, the median upward gaze velocity was 15% of yaw head velocity for patients and <1% for normal subjects ( P < 0.001). Upward eye velocity was greater in the contralateral (abducting) eye during yaw and in the ipsilateral eye during roll. Patients had a higher gain (eye speed/head speed) for downward than for upward pitch (median ratio of downward to upward gain: 1.3). In patients, upward gaze velocities during both yaw and roll correlated with the difference in anterior (AC) and posterior canal excitations, scaled by the respective pitch gains. Our findings support the hypothesis that upward eye velocity during yaw results from AC excitation, which must normally be suppressed by the intact cerebellum.

Characterization and adaptive modification of the goldfish vestibuloocular reflex by sinusoidal and velocity step vestibular stimulation

1992 ◽  
Vol 68 (6) ◽  
pp. 2003-2015 ◽  
Author(s):  
A. M. Pastor ◽  
R. R. de la Cruz ◽  
R. Baker
Keyword(s):  
Electrical Stimulation ◽  
Eye Movement ◽  
Constant Velocity ◽  
Directional Asymmetry ◽  
Vestibuloocular Reflex ◽  
Dynamic Component ◽  
Head Velocity ◽  
Vor Adaptation ◽  
Eye Velocity ◽  
Stimulation Of

1. The normal and adapted vestibuloocular reflex (VOR) of goldfish was characterized by means of sinusoidal, velocity step, and position step head rotations about the vertical axis. VOR adaptation was induced by short-term, 1- to 4-h, presentation of visual and vestibular stimuli that altered the ratio of eye to head velocity. 2. The VOR response measured with sinusoidal oscillations in the dark was close to ideal compensatory values over 2 decades (1/32-2 Hz). Gain approximated unity, and phase, in relation to the head, was nearly 180 degrees. The VOR was linear within the range of head velocity tested (4-64 degrees/s). 3. Head velocity steps from 1/8 to 1 Hz produced steplike eye velocity profiles that could be divided into an early acceleration-related "dynamic" component and a later constant-velocity "sustained" period frequently separated by a sag at approximately 0.1-0.15 s from the initiation of eye movement. The sustained response exhibited no decay during the constant-velocity component of the step. 4. Higher temporal resolution of the dynamic response showed the adducting eye movement to have a shorter latency, faster rise time, and larger peak gain than the abducting eye movement. The characteristics of this directional asymmetry were similar for position steps and electrical stimulation of the vestibular nerve. However, the asymmetry was not observed during sinusoidal head rotation, the sustained component of the step response, or after electrical stimulation of the VIth and IIIrd nerves. We conclude that this directional asymmetry is of central origin and may be largely due to the parallel vestibular and abducens internuclear neuron pathways onto medial rectus motoneurons. 5. The VOR adaptation process for both higher and lower eye velocity exhibited an exponential time course with time constants of 55 and 45 min, respectively. After continuous sinusoidal training for 4 h, VOR gain reached an asymptotic level 5% away from perfect suppression in the low-gain training, but 19% away from the actual performance in the high-gain paradigm. The time constant for VOR gain reversal was 5 h, and an asymptotic level 40% less than performance was reached within 10 h. 6. Adapted VOR gain was symmetrical for both directions of eye movement measured either during sinusoidal rotation or the sustained part of the velocity step. VOR adaptation also produced a comparable gain change in the nasal and temporal directions of the dynamic component, but this reflected the asymmetric characteristics observed in the preadapted condition.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Vestibuloocular Reflex Adaptation Investigated With Chronic Motion-Modulated Electrical Stimulation of Semicircular Canal Afferents

2010 ◽  
Vol 103 (2) ◽  
pp. 1066-1079 ◽  
Author(s):  
Richard F. Lewis ◽  
Csilla Haburcakova ◽  
Wangsong Gong ◽  
Chadi Makary ◽  
Daniel M. Merfeld
Keyword(s):  
Electrical Stimulation ◽  
High Sensitivity ◽  
Rotational Axis ◽  
Vestibuloocular Reflex ◽  
Chronic Stimulation ◽  
Unilateral Stimulation ◽  
Electrical Pulses ◽  
Vor Adaptation ◽  
Low Sensitivity ◽  
The Brain

To investigate vestibuloocular reflex (VOR) adaptation produced by changes in peripheral vestibular afference, we developed and tested a vestibular “prosthesis” that senses yaw-axis angular head velocity and uses this information to modulate the rate of electrical pulses applied to the lateral canal ampullary nerve. The ability of the brain to adapt the different components of the VOR (gain, phase, axis, and symmetry) during chronic prosthetic electrical stimulation was studied in two squirrel monkeys. After characterizing the normal yaw-axis VOR, electrodes were implanted in both lateral canals and the canals were plugged. The VOR in the canal-plugged/instrumented state was measured and then unilateral stimulation was applied by the prosthesis. The VOR was repeatedly measured over several months while the prosthetic stimulation was cycled between off, low-sensitivity, and high-sensitivity stimulation states. The VOR response initially demonstrated a low gain, abnormal rotational axis, and substantial asymmetry. During chronic stimulation the gain increased, the rotational axis improved, and the VOR became more symmetric. Gain changes were augmented by cycling the stimulation between the off and both low- and high-sensitivity states every few weeks. The VOR time constant remained low throughout the period of chronic stimulation. These results demonstrate that the brain can adaptively modify the gain, axis, and symmetry of the VOR when provided with chronic motion-modulated electrical stimulation by a canal prosthesis.

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