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https://www.readbyqxmd.com/read/27153330/stability-of-the-avor-to-repeat-head-impulse-testing
#1
Michael C Schubert, Americo A Migliaccio
OBJECTIVE: The angular vestibulo-ocular reflex (aVOR) is known to be influenced by factors such as arousal and cognition during traditional vestibular function testing. However, the inherent variability of the aVOR to head impulse testing has not been explicitly examined. The purpose of this study was to determine the variability of the aVOR to active and passive head impulses using the gold standard scleral search coil method to record head and eye rotation. STUDY DESIGN: Descriptive...
July 2016: Otology & Neurotology
https://www.readbyqxmd.com/read/27093033/test-retest-and-interrater-reliability-of-the-video-head-impulse-test-in-the-pediatric-population
#2
Lynda Marie Ross, Janet Odry Helminski
OBJECTIVE: Determine reliability of horizontal and vertical video head impulse test (vHIT) and effect of maturation on angular vestibular ocular reflex (AVOR) gain estimations and peak head velocities of individual canals in typically developing children and adolescents. DESIGN: Reliability study. SETTING: University research laboratory SUBJECTS: : Two normal adults mean age 51.5 ± 0.5 years and 28 typically developing children and adolescents mean age 10 ± 3...
June 2016: Otology & Neurotology
https://www.readbyqxmd.com/read/25709578/hybrid-model-of-the-context-dependent-vestibulo-ocular-reflex-implications-for-vergence-version-interactions
#3
Mina Ranjbaran, Henrietta L Galiana
The vestibulo-ocular reflex (VOR) is an involuntary eye movement evoked by head movements. It is also influenced by viewing distance. This paper presents a hybrid nonlinear bilateral model for the horizontal angular vestibulo-ocular reflex (AVOR) in the dark. The model is based on known interconnections between saccadic burst circuits in the brainstem and ocular premotor areas in the vestibular nuclei during fast and slow phase intervals of nystagmus. We implemented a viable switching strategy for the timing of nystagmus events to allow emulation of real nystagmus data...
2015: Frontiers in Computational Neuroscience
https://www.readbyqxmd.com/read/25564082/acute-vor-gain-differences-for-outward-vs-inward-head-impulses
#4
Michael C Schubert, Georgios Mantokoudis, Li Xie, Yuri Agrawal
BACKGROUND: Vestibular rehabilitation is a sub-specialization within the practice of physical therapy that includes treatments designed to reduce gaze instability. Gaze stability exercises are commonly given for head rotations to the left and right, even in subjects with one healthy vestibular system (as in unilateral loss). Few studies have investigated the difference in the angular vestibular ocular reflex gain (aVOR) measured in the acute phase after deafferentation for ipsilesional head rotations that move the head away from center or towards center...
2014: Journal of Vestibular Research: Equilibrium & Orientation
https://www.readbyqxmd.com/read/25253747/head-impulse-gain-and-saccade-analysis-in-pontine-cerebellar-stroke-and-vestibular-neuritis
#5
Luke Chen, Michael Todd, Gabor M Halmagyi, Swee Aw
OBJECTIVE: We sought to quantify and compare angular vestibulo-ocular reflex (aVOR) gain and compensatory saccade properties elicited by the head impulse test (HIT) in pontine-cerebellar stroke (PCS) and vestibular neuritis (VN). METHODS: Horizontal HIT was recorded ≤7 days from vertigo onset with dual-search coils in 33 PCS involving the anterior inferior, posterior inferior, and superior cerebellar arteries (13 AICA, 17 PICA, 3 SCA) confirmed by MRI and 20 VN...
October 21, 2014: Neurology
https://www.readbyqxmd.com/read/24448289/vestibular-dysfunction-in-turner-syndrome-a-case-report
#6
Michael Baxter, Yuri Agrawal
OBJECTIVE: Turner syndrome is a well-known cause of sensorineural hearing loss, and the lack of estrogen has been implicated in cochlear dysfunction. It has never been associated with vestibular dysfunction. We report a case of a patient with Turner syndrome who was found to have bilateral vestibular dysfunction based on video-oculography (VOG) testing. PATIENT: A single patient with a history of Turner syndrome who was found to have significant bilateral vestibular dysfunction...
February 2014: Otology & Neurotology
https://www.readbyqxmd.com/read/24298265/a-new-tool-for-investigating-the-functional-testing-of-the-vor
#7
Paolo Colagiorgio, Silvia Colnaghi, Maurizio Versino, Stefano Ramat
Peripheral vestibular function may be tested quantitatively, by measuring the gain of the angular vestibulo-ocular reflex (aVOR), or functionally, by assessing how well the aVOR performs with respect to its goal of stabilizing gaze in space and thus allow to acquire visual information during the head movement. In recent years, several groups have developed clinical and quantitative approaches to functional testing of the vestibular system based on the ability to identify an optotype briefly displayed on screen during head rotations...
2013: Frontiers in Neurology
https://www.readbyqxmd.com/read/24218543/velocity-storage-mechanism-in-zebrafish-larvae
#8
Chien-Cheng Chen, Christopher J Bockisch, Giovanni Bertolini, Itsaso Olasagasti, Stephan C F Neuhauss, Konrad P Weber, Dominik Straumann, Melody Ying-Yu Huang
The optokinetic reflex (OKR) and the angular vestibulo-ocular reflex (aVOR) complement each other to stabilize images on the retina despite self- or world motion, a joint mechanism that is critical for effective vision. It is currently hypothesized that signals from both systems integrate, in a mathematical sense, in a network of neurons operating as a velocity storage mechanism (VSM). When exposed to a rotating visual surround, subjects display the OKR, slow following eye movements frequently interrupted by fast resetting eye movements...
January 1, 2014: Journal of Physiology
https://www.readbyqxmd.com/read/24111014/hybrid-nonlinear-model-of-the-angular-vestibulo-ocular-reflex
#9
Mina Ranjbaran, Henrietta L Galiana
A hybrid nonlinear bilateral model for the horizontal angular vestibulo-ocular reflex (AVOR) is presented in this paper. The model relies on known interconnections between saccadic burst circuits in the brainstem and ocular premotor areas in the vestibular nuclei during slow and fast phase intervals. A viable switching strategy for the timing of nystagmus events is proposed. Simulations show that this hybrid model replicates AVOR nystagmus patterns that are observed in experimentally recorded data.
2013: Conference Proceedings: Annual International Conference of the IEEE Engineering in Medicine and Biology Society
https://www.readbyqxmd.com/read/24080977/evaluation-of-quantitative-head-impulse-testing-using-search-coils-versus-video-oculography-in-older-individuals
#10
Yuri Agrawal, Michael C Schubert, Americo A Migliaccio, David S Zee, Erich Schneider, Nadine Lehnen, John P Carey
OBJECTIVE: To evaluate the validity of 2D video-oculography (VOG) compared with scleral search coils for horizontal AVOR gain estimation in older individuals. STUDY DESIGN: Cross-sectional validation study. SETTING: Tertiary care academic medical center. PATIENTS: Six individuals age 70 and older. INTERVENTIONS: Simultaneous eye movement recording with scleral search coil (over right eye) and EyeSeeCam VOG camera (over left eye) during horizontal head impulses...
February 2014: Otology & Neurotology
https://www.readbyqxmd.com/read/23925341/continuous-theta-burst-stimulation-of-the-right-superior-temporal-gyrus-impairs-self-motion-perception
#11
A A Tarnutzer, A G Lasker, D S Zee
Sensory input from the semicircular canals (SCC) and otolith organs is centrally combined with signals from other sensory modalities to continuously update the internal estimate of self-motion. Constant velocity vertical on-axis rotation leads to decay of the nystagmus response from the horizontal SCC and of perceived angular velocity (PAV), and when the rotation stops, a similar oppositely directed post-rotatory response occurs. Case reports and electrical stimulation studies suggest an involvement of the temporo-peri-Sylvian vestibular cortex in generating the PAV...
October 2013: Experimental Brain Research. Experimentelle Hirnforschung. Expérimentation Cérébrale
https://www.readbyqxmd.com/read/23366772/the-horizontal-angular-vestibulo-ocular-reflex-a-non-linear-mechanism-for-context-dependent-responses
#12
Mina Ranjbaran, Henrietta L Galiana
A bilateral model for the horizontal angular vestibulo-ocular reflex (AVOR) is presented in this paper. It is shown that by assigning proper non-linear neural computations at the premotor level, the model is capable of replicating target-distance dependent VOR responses. Moreover, the model behavior in case of sensory plugging is also consistent with reported experimental observations.
2012: Conference Proceedings: Annual International Conference of the IEEE Engineering in Medicine and Biology Society
https://www.readbyqxmd.com/read/23162043/sleep-deprivation-has-no-effect-on-dynamic-visual-acuity-in-military-service-members-who-are-healthy
#13
Matthew R Scherer, Pedro J Claro, Kristin J Heaton
BACKGROUND: The risk of traumatic brain injury (TBI) and comorbid posttraumatic dizziness is elevated in military operational environments. Sleep deprivation is known to affect a service member's performance while deployed, although little is known about its effects on vestibular function. Recent findings suggest that moderate acceleration step rotational stimuli may elicit a heightened angular vestibulo-ocular reflex (aVOR) response relative to low-frequency sinusoidal stimuli after 26 hours of sleep deprivation...
September 2013: Physical Therapy
https://www.readbyqxmd.com/read/23150093/transmastoid-galvanic-stimulation-does-not-affect-the-vergence-mediated-gain-increase-of-the-human-angular-vestibulo-ocular-reflex
#14
Americo A Migliaccio, Charles C Della Santina, John P Carey
Vergence is one of several viewing contexts that require an increase in the angular vestibular-ocular reflex (aVOR) response. A previous monkey study found that the vergence-mediated gain (eye/head velocity) increase of the aVOR was attenuated by 64 % when anodic currents, which preferentially lower the activity of irregularly firing vestibular afferents, were delivered to both labyrinths. We sought to determine whether there was similar evidence implicating a role for irregular afferents in the vergence-mediated gain increase of the human aVOR...
February 2013: Experimental Brain Research. Experimentelle Hirnforschung. Expérimentation Cérébrale
https://www.readbyqxmd.com/read/22660376/modeling-spatial-tuning-of-adaptation-of-the-angular-vestibulo-ocular-reflex
#15
Yongqing Xiang, Sergei B Yakushin, Theodore Raphan
Gain adaptation of the yaw angular vestibular ocular reflex (aVOR) induced in side-down positions has gravity-independent (global) and -dependent (localized) components. When the head oscillation angles are small during adaptation, localized gain changes are maximal in the approximate position of adaptation. Concurrently, polarization vectors of canal-otolith vestibular neurons adapt their orientations during these small-angle adaptation paradigms. Whether there is orientation adaptation with large amplitude head oscillations, when the head is not localized to a specific position, is unknown...
July 2012: Experimental Brain Research. Experimentelle Hirnforschung. Expérimentation Cérébrale
https://www.readbyqxmd.com/read/22526736/the-under-compensatory-roll-avor-does-not-affect-dynamic-visual-acuity
#16
Michael C Schubert, Americo A Migliaccio, Tammy W C Ng, Aasef G Shaikh, David S Zee
Rotations of the head evoke compensatory reflexive eye rotations in the orbit to stabilize images onto the fovea. In normal humans, the angular vestibulo-ocular reflex (aVOR) gain (eye/head velocity) changes depending on the head rotation plane. For pitch and yaw head rotations, the gain is near unity, but during roll head rotations, the aVOR gain is ∼ 0.7. The purpose of this study was to determine whether this physiological discrepancy affects dynamic visual acuity (DVA)--a functional measure of the aVOR that requires subjects to identify letters of varying acuities during head rotation...
August 2012: Journal of the Association for Research in Otolaryngology: JARO
https://www.readbyqxmd.com/read/22402905/-receptor-function-of-the-semicircular-canals-part-2-pathophysiology-diseases-clinical-findings-and-treatment-aspects
#17
A Blödow, M Bloching, K Hörmann, L E Walther
Perturbation of semicircular canal function may result in a pathological angular vestibulo-ocular reflex (aVOR). The resulting impairment in gaze stabilization is perceived as "vertigo" or "dizziness" and may occur following receptor function impairment of all three semicircular canals. The head impulse test reveals hidden (covert-catchup) or visible (overt-catchup) saccades in disturbances of semicircular function. Most peripheral vestibular disorders can be treated conservatively. There are surgical treatment options for some diseases, such as intractable benign paroxysmal positional vertigo and superior semicircular canal dehiscence...
March 2012: HNO
https://www.readbyqxmd.com/read/22402654/tuning-of-gravity-dependent-and-gravity-independent-vertical-angular-vor-gain-changes-by-frequency-of-adaptation
#18
Sergei B Yakushin
The gain of the vertical angular vestibulo-ocular reflex (aVOR) was adaptively increased and decreased in a side-down head orientation for 4 h in two cynomolgus monkeys. Adaptation was performed at 0.25, 1, 2, or 4 Hz. The gravity-dependent and -independent gain changes were determined over a range of head orientations from left-side-down to right-side-down at frequencies from 0.25 to 10 Hz, before and after adaptation. Gain changes vs. frequency data were fit with a Gaussian to determine the frequency at which the peak gain change occurred, as well as the tuning width...
June 2012: Journal of Neurophysiology
https://www.readbyqxmd.com/read/22255099/chronic-stimulation-of-the-semicircular-canals-using-a-multichannel-vestibular-prosthesis-effects-on-locomotion-and-angular-vestibulo-ocular-reflex-in-chinchillas
#19
Daniel Q Sun, Mehdi A Rahman, Gene Fridman, Chenkai Dai, Bryce Chiang, Charles C Della Santina
Bilateral loss of vestibular sensation causes difficulty maintaining stable vision, posture and gait. An implantable prosthesis that partly restores vestibular sensation could significantly improve quality of life for individuals disabled by this disorder. We have developed a head-mounted multichannel vestibular prosthesis (MVP) that restores sufficient semicircular canal function to recreate a 3D angular vestibulo-ocular reflex (aVOR). In this study, we evaluated effects of chronic MVP stimulation on locomotion in chinchillas...
2011: Conference Proceedings: Annual International Conference of the IEEE Engineering in Medicine and Biology Society
https://www.readbyqxmd.com/read/21950996/orientation-adaptation-of-eye-movement-related-vestibular-neurons-due-to-prolonged-head-tilt
#20
Olga V Kolesnikova, Theodore Raphan, Bernard Cohen, Sergei B Yakushin
Sixteen neurons, including vestibular-only (VO), eye-head velocity (EHV), and position-vestibular-pause (PVP) neurons sensitive to head tilt were recorded in the rostromedial and in superior vestibular nuclei. Projection of the otolith polarization vector to the horizontal plane (response vector orientation [RVO]) was determined before and after prolonged head orientation in side-down position. The RVO of VO neurons shifted toward alignment with the axis of gravity when the head was in the position of adaptation...
September 2011: Annals of the New York Academy of Sciences
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