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Kerkeni H, Zee DS, Korda A, Morrison M, Mantokoudis G, Ramat S. Corrective saccades in acute vestibular neuritis: studying the role of prediction with automated passively induced head impulses. J Neurophysiol 2023; 129:445-454. [PMID: 36651642 DOI: 10.1152/jn.00382.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
When the demands for visual stabilization during head rotations overwhelm the ability of the vestibuloocular reflex (VOR) to produce compensatory eye movements, the brain produces corrective saccades that bring gaze toward the fixation target, even without visual cues (covert saccades). What triggers covert saccades and what might be the role of prediction in their generation are unknown. We studied 14 subjects with acute vestibular neuritis. To minimize variability of the stimulus, head impulses were imposed with a motorized torque generator with the subject on a bite bar. Predictable and unpredictable (timing, amplitude, direction) stimuli were compared. Distributions of covert corrective saccade latencies were analyzed with a "LATER" (linear approach to threshold with ergodic rate) approach. On the affected side, VOR gain was higher (0.47 ± 0.28 vs. 0.39 ± 0.22, P ≪ 0.001) with predictable than unpredictable head impulses, and gaze error at the end of the head movement was less (5.4 ± 3.3° vs. 6.9 ± 3.3°, P ≪ 0.001). Analyzing trials with covert saccades, gaze error at saccade end was significantly less with predictable than unpredictable head impulses (4.2 ± 2.8° vs. 5.5 ± 3.2°, P ≪ 0.001). Furthermore, covert corrective saccades occurred earlier with predictable than unpredictable head impulses (140 ± 37 vs. 153 ± 37 ms, P ≪ 0.001). Using a LATER analysis with reciprobit plots, we were able to divide covert corrective saccades into two classes, early and late, with a break point in the range of 88-98 ms. We hypothesized two rise-to-threshold decision mechanisms for triggering early and late covert corrective saccades, with the first being most engaged when stimuli are predictable.NEW & NOTEWORTHY We successfully used a LATER (linear approach to threshold with ergodic rate) analysis of the latencies of corrective saccades in patients with acute vestibular neuritis. We found two types of covert saccades: early (<90 ms) and late (>90 ms) covert saccades. Predictability led to an increase in VOR gain and a decrease in saccade latency.
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Affiliation(s)
- Hassen Kerkeni
- Department of Neurology, Inselspital, University Hospital Bern, University of Bern, Bern, Switzerland
| | - David S Zee
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - Athanasia Korda
- Department of Otorhinolaryngology, Head and Neck Surgery, Inselspital, University Hospital Bern, University of Bern, Bern, Switzerland
| | - Miranda Morrison
- Department of Otorhinolaryngology, Head and Neck Surgery, Inselspital, University Hospital Bern, University of Bern, Bern, Switzerland
| | - Georgios Mantokoudis
- Department of Otorhinolaryngology, Head and Neck Surgery, Inselspital, University Hospital Bern, University of Bern, Bern, Switzerland
| | - Stefano Ramat
- Laboratory of Bioengineering, Department of Electrical, Computer and Biomedical Engineering, University of Pavia, Pavia, Italy
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The human vestibulo-ocular reflex and compensatory saccades in schwannoma patients before and after vestibular nerve section. Clin Neurophysiol 2022; 138:197-213. [DOI: 10.1016/j.clinph.2022.02.014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Revised: 01/25/2022] [Accepted: 02/13/2022] [Indexed: 11/19/2022]
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Emekci T, Erbek HS. The relationship between functional head impulse test and age in healthy individuals. J Vestib Res 2021; 32:123-134. [PMID: 34120922 DOI: 10.3233/ves-210040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
BACKGROUND fHIT is an easily applicable test battery that indirectly evaluates the vestibulo-ocular reflex (VOR) from a functional perspective. AIMS/OBJECTIVES The aim of this study was to Individuals determine the correlation between age and the percentage of correct answers (% CA) obtained in the functional head impulse test (fHIT) in healthy individuals. MATERIAL AND METHODS A total of 105 volunteers, 50 males and 55 females, between the ages of 18 and 70 years, participated in the study. A Beon Solution fHIT system (Zero Branco (TV), Italy) was used in the study. RESULTS In our study, a decrease in the mean % CA was observed in all semicircular canals (SCCs) with increasing age. Between age and mean % CA, a significant negative moderate (-0.311) correlation was observed in lateral SCCs, and a significant negative low (-0.257) correlation was observed in posterior SCCs (p < 0.05). In anterior SCCs, there was no statistically significant relationship between age and mean % CA (p > 0.05). CONCLUSIONS The present study performed in a healthy population will be helpful in terms of making comparisons in studies to be conducted in various vestibular diseases. It will also be a guide for identifying pathological consequences in vestibular diseases.
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Affiliation(s)
- Tuğba Emekci
- Necmettin Erbakan University, Faculty of Medicine ENT Clinic, Konya, Turkey
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Zangemeister WH, Heesen C, Röhr D, Gold SM. Oculomotor Fatigue and Neuropsychological Assessments mirror Multiple Sclerosis Fatigue. J Eye Mov Res 2020; 13:10.16910/jemr.13.4.6. [PMID: 33828807 PMCID: PMC8006090 DOI: 10.16910/jemr.13.4.6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Fatigue is a major complaint in MS. Up to now no objective assessment tools have been established which hampers any treatment approach. Previous work has indicated an association of fatigue with cognitive measures of attention. Oculomotor tests have been established in healthy individuals as a read-out of fatigue, and to some extent in MS patients. Based on these observations we compared two groups of MS patients, one with fatigue (n=28) and one without fatigue (n=21) and a group of healthy subjects (n=15) with a standardised computerised measure of alertness and an oculomotor stress test. Patients with fatigue showed highly significant changes of their saccade dynamics as defined by the Main Sequence and Phase Plane plots: They showed slowing of saccades, the characteristical fatigue double peak, and an asymmetrical phase plane. Oculomotor tests differentiated significantly between fatigue and fatigabiliy in our MS patients. They also showed significantly worse performance in the alertness test as well as in the oculomotor task. Significantly slower reaction times were observed for tonic alertness in 2 series without a cue (p=.025 and p=.037) but not in phasic alertness with a cue (p=.24 and p=.34). Performance was influenced by disability as well as by affective state. We conclude, when controlling for disability and depression, saccadic stress tests and alertness tests could be used as an objective read-out for fatigability and fatigue in MS patients.
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Affiliation(s)
| | | | - Dorit Röhr
- University Medical Center Hamburg-Eppendorf, Germany
| | - Stefan M Gold
- University Medical Center Hamburg-Eppendorf, Germany
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Li Z, Wang H, Wang H, Yu D. Quantitative Analysis of Saccade Gain in Video Head Impulse Testing. Otolaryngol Head Neck Surg 2020; 163:799-805. [PMID: 32513047 DOI: 10.1177/0194599820930669] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE To quantitatively analyze corrective saccade (CS) gain and further characterize the specific relationship between vestibulo-ocular reflex (VOR) gain and CS gain in patients with vestibular loss and healthy controls. STUDY DESIGN Prospective combined with retrospective study. SETTING Affiliated Sixth People's Hospital, Shanghai Jiao Tong University. SUBJECTS AND METHODS Forty patients with unilateral vestibular loss and 40 participants with normal vestibular function were subjected to video head impulse testing (vHIT). The analysis of the horizontal semicircular canal VOR and CS gains was based on individual head impulses. RESULTS The patient group had significantly higher CS gain and lower VOR gain than the control group (P < .001). While there was no significant correlation between VOR and CS gains in the control group after adjusting for age and sex (P = .689), VOR gain negatively correlated with CS gain in the patient group (r = -0.853, P < .001). The specific relationship between VOR and CS gains was characterized as y = -1.17x + 1.12 (x: VOR gain, y: CS gain; r 2 = 0.732, P < .001) in the patient group. CONCLUSIONS In healthy participants, CS was not correlated with VOR gain, suggesting that CS is not due to VOR hypofunction. In patients with unilateral vestibular loss, CS was closely associated with VOR gain and can almost correct gaze position errors required for visual stabilization. CS gain could be an important indicator to diagnose vestibular loss and help physicians identify abnormal vHIT curves caused by artifacts and irregular practices.
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Affiliation(s)
- Zhuangzhuang Li
- Department of Otolaryngology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, China.,Key Laboratory of Sleep Disordered Breathing, Shanghai, China
| | - Haiyan Wang
- Eye and ENT Hospital of Fu Dan University, Shanghai, China
| | - Hui Wang
- Department of Otolaryngology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, China.,Key Laboratory of Sleep Disordered Breathing, Shanghai, China
| | - Dongzhen Yu
- Department of Otolaryngology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, China.,Key Laboratory of Sleep Disordered Breathing, Shanghai, China
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Pogson JM, Taylor RL, McGarvie LA, Bradshaw AP, D’Souza M, Flanagan S, Kong J, Halmagyi GM, Welgampola MS. Head impulse compensatory saccades: Visual dependence is most evident in bilateral vestibular loss. PLoS One 2020; 15:e0227406. [PMID: 31940394 PMCID: PMC6961882 DOI: 10.1371/journal.pone.0227406] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2019] [Accepted: 12/18/2019] [Indexed: 11/19/2022] Open
Abstract
The normal vestibulo-ocular reflex (VOR) generates almost perfectly compensatory smooth eye movements during a 'head-impulse' rotation. An imperfect VOR gain provokes additional compensatory saccades to re-acquire an earth-fixed target. In the present study, we investigated vestibular and visual contributions on saccade production. Eye position and velocity during horizontal and vertical canal-plane head-impulses were recorded in the light and dark from 16 controls, 22 subjects after complete surgical unilateral vestibular deafferentation (UVD), eight subjects with idiopathic bilateral vestibular loss (BVL), and one subject after complete bilateral vestibular deafferentation (BVD). When impulses were delivered in the horizontal-canal plane, in complete darkness compared with light, first saccade frequency mean(SEM) reduced from 96.6(1.3)-62.3(8.9) % in BVL but only 98.3(0.6)-92.0(2.3) % in UVD; saccade amplitudes reduced from 7.0(0.5)-3.6(0.4) ° in BVL but were unchanged 6.2(0.3)-5.5(0.6) ° in UVD. In the dark, saccade latencies were prolonged in lesioned ears, from 168(8.4)-240(24.5) ms in BVL and 177(5.2)-196(5.7) ms in UVD; saccades became less clustered. In BVD, saccades were not completely abolished in the dark, but their amplitudes decreased from 7.3-3.0 ° and latencies became more variable. For unlesioned ears (controls and unlesioned ears of UVD), saccade frequency also reduced in the dark, but their small amplitudes slightly increased, while latency and clustering remained unchanged. First and second saccade frequencies were 75.3(4.5) % and 20.3(4.1) %; without visual fixation they dropped to 32.2(5.0) % and 3.8(1.2) %. The VOR gain was affected by vision only in unlesioned ears of UVD; gains for the horizontal-plane rose slightly, and the vertical-planes reduced slightly. All head-impulse compensatory saccades have a visual contribution, the magnitude of which depends on the symmetry of vestibular-function and saccade latency: BVL is more profoundly affected by vision than UVD, and second saccades more than first saccades. Saccades after UVD are probably triggered by contralateral vestibular function.
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Affiliation(s)
- Jacob M. Pogson
- Royal Prince Alfred Hospital, Institute of Clinical Neuroscience, Camperdown, New South Wales, Australia
- Faculty of Health and Medicine, Sydney Medical School, The University of Sydney, Camperdown, New South Wales, Australia
| | - Rachael L. Taylor
- Royal Prince Alfred Hospital, Institute of Clinical Neuroscience, Camperdown, New South Wales, Australia
- Faculty of Health and Medicine, Sydney Medical School, The University of Sydney, Camperdown, New South Wales, Australia
| | - Leigh A. McGarvie
- Royal Prince Alfred Hospital, Institute of Clinical Neuroscience, Camperdown, New South Wales, Australia
- Department of Psychology, Faculty of Science, The University of Sydney, Camperdown, New South Wales, Australia
| | - Andrew P. Bradshaw
- Royal Prince Alfred Hospital, Institute of Clinical Neuroscience, Camperdown, New South Wales, Australia
| | - Mario D’Souza
- Department of Clinical Research, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia
| | - Sean Flanagan
- Otolaryngology, Head and Neck and Skull Base Surgery, St Vincent’s Hospital, Darlinghurst, New South Wales, Australia
- Faculty of Medicine, University of NSW, Kensington, New South Wales, Australia
| | - Jonathan Kong
- Faculty of Health and Medicine, Sydney Medical School, The University of Sydney, Camperdown, New South Wales, Australia
- Department of Neurosurgery, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia
- Department of Otolaryngology, Head & Neck Surgery, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia
| | - G. Michael Halmagyi
- Royal Prince Alfred Hospital, Institute of Clinical Neuroscience, Camperdown, New South Wales, Australia
- Faculty of Health and Medicine, Sydney Medical School, The University of Sydney, Camperdown, New South Wales, Australia
| | - Miriam S. Welgampola
- Royal Prince Alfred Hospital, Institute of Clinical Neuroscience, Camperdown, New South Wales, Australia
- Faculty of Health and Medicine, Sydney Medical School, The University of Sydney, Camperdown, New South Wales, Australia
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Pogson JM, Taylor RL, Bradshaw AP, McGarvie L, D’Souza M, Halmagyi GM, Welgampola MS. The human vestibulo-ocular reflex and saccades: normal subjects and the effect of age. J Neurophysiol 2019; 122:336-349. [DOI: 10.1152/jn.00847.2018] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Here we characterize in 80 normal subjects (16–84 yr (means ± SD, 47 ± 19 yr) the vestibulo-ocular reflex (VOR) and saccades in response to three-dimensional head impulses with a monocular video head impulse test (vHIT) of the right eye. Impulses toward the right lateral, right anterior, and left posterior canals (means: 0.98, 0.91, 0.79) had slightly higher mean gains compared with their counterparts (0.95, 0.86, 0.76). In the older age group (>60 yr), gains of the left posterior canal dropped 0.09 and left anterior canals rose 0.09 resulting in symmetry. All canal gains reduced with increasing head velocity (0.02–0.13 per 100°/s). Comparison of lateral canal gains calculated using five published algorithms yielded lower values (~0.80) when a narrow detection window was used. Low-amplitude refixation saccades (amplitude: 1.11 ± 0.98°, peak velocity: 63.9 ± 34.0°/s at 262.0 ± 93.9 ms) were observed among all age groups (frequency: 40.2 ± 23.4%), increasing in amplitude, peak velocity, and frequency in older subjects. Impulses toward anterior canals showed the least frequent saccades and lateral and posterior canals were similar, but lateral canal impulses showed the smallest saccades and the posterior canal showed the largest saccades. Saccade peak-velocity approximate amplitude “main sequence” slope was steeper for the horizontal canals compared with the vertical planes (60 vs. <40°/s per 1°). In summary, we found small but significant asymmetries in monocular vHIT gain that changed with age. Healthy subjects commonly have minuscule refixation saccades that are moderately to strongly correlated with vHIT gain. NEW & NOTEWORTHY Gaze fixation is normally stabilized during rapid “head-impulse” movements by the bisynaptic vestibulo-ocular reflex (VOR), but earlier studies of normal subjects also report small amplitude saccades. We found that with increased age of the subject the vertical VOR became more variable, while in all semicircular canal directions the saccade frequency, amplitude, and peak velocity increased. We also found that the VOR gain algorithm significantly influences values.
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Affiliation(s)
- Jacob M. Pogson
- Sydney Medical School, The University of Sydney, Camperdown, New South Wales, Australia
- Institute of Clinical Neuroscience, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia
| | - Rachael L. Taylor
- Institute of Clinical Neuroscience, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia
- Department of Physiology, University of Auckland, Auckland, New Zealand
| | - Andrew P. Bradshaw
- Institute of Clinical Neuroscience, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia
| | - Leigh McGarvie
- Psychology Department, The University of Sydney, Camperdown, New South Wales, Australia
- Institute of Clinical Neuroscience, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia
| | - Mario D’Souza
- Sydney Medical School, The University of Sydney, Camperdown, New South Wales, Australia
- Clinical Research Centre, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia
| | - G. Michael Halmagyi
- Sydney Medical School, The University of Sydney, Camperdown, New South Wales, Australia
- Institute of Clinical Neuroscience, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia
| | - Miriam S. Welgampola
- Sydney Medical School, The University of Sydney, Camperdown, New South Wales, Australia
- Institute of Clinical Neuroscience, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia
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Romano F, Bertolini G, Agostino D, Straumann D, Ramat S, Feddermann-Demont N. Functional Head Impulse Test in Professional Athletes: Sport-Specific Normative Values and Implication for Sport-Related Concussion. Front Neurol 2019; 10:387. [PMID: 31130909 PMCID: PMC6509415 DOI: 10.3389/fneur.2019.00387] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2019] [Accepted: 03/29/2019] [Indexed: 02/05/2023] Open
Abstract
Dizziness, slow visual tracking, or blurred vision following active head (or body) movements are among the most common symptoms reported following sport-related concussion, often related to concurrent dysfunctions of the vestibular system. In some cases, symptoms persist even if bedside and auxiliary standard vestibular tests are unremarkable. New functional tests have been developed in recent years to objectify neurological alterations that are not captured by standard tests. The functional head impulse test (fHIT) requires the patient to recognize an optotype that is briefly flashed during head rotations with various angular accelerations (2,001–6,000 deg/s2) and assesses the proportion if correct answers (pca). 268 active professional athletes (23.70 ± 5.32y) from six different sports were tested using fHIT. Pca were analyzed both pooling head acceleration in the range of 2,001–6,000 deg/s2 and computing a single pca value for each 1,000 deg/s2 bin in the range 2,001–8,000 deg/s2. No significant difference (p = 0.159) was found between responses to head impulses in the plane of horizontal (pca: 0.977) and vertical semicircular canals (pca: 0.97). The sport practiced had a major effect on the outcome of the fHIT. Handball players achieved a better performance (p < 0.001) than the whole athlete group, irrespective of the direction of head impulses. The pca achieved by athletes practicing snowboard, bob and skeleton were instead significantly below those of the whole athlete group (p < 0.001) but only when vertical head impulses were tested. Overall, pca declined with increasing head acceleration. The decline was particularly evident in the range not included in the standard fHIT exam, i.e., 6,001–8,000 deg/s2 for horizontal and 5,001–8,000 deg/s2 for vertical head impulses. When vertical head impulses were tested, athletes practicing snowboard, bob and skeleton (non-ball sports) showed, beside the lower overall pca, also a steeper decline as a function of vertical head acceleration. The findings suggest that: (1) functional VOR testing can help understanding sport-specific VOR requirements; (2) the fHIT is able to detect and objectify subtle, sport-specific changes of functional VOR performance; (3) if sport-specific normative values are used, the fHIT test procedure needs to be optimized, starting from the highest acceleration to minimize the number of head impulses.
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Affiliation(s)
- Fausto Romano
- Department of Neurology, University of Zurich, Zurich, Switzerland.,Clinical Neuroscience Center, University Hospital of Zürich, Zurich, Switzerland.,Swiss Concussion Center, Zurich, Switzerland
| | - Giovanni Bertolini
- Department of Neurology, University of Zurich, Zurich, Switzerland.,Clinical Neuroscience Center, University Hospital of Zürich, Zurich, Switzerland.,Swiss Concussion Center, Zurich, Switzerland
| | | | - Dominik Straumann
- Department of Neurology, University of Zurich, Zurich, Switzerland.,Clinical Neuroscience Center, University Hospital of Zürich, Zurich, Switzerland.,Swiss Concussion Center, Zurich, Switzerland
| | - Stefano Ramat
- Department of Computer, Electric and Biomedical Engineering, University of Pavia, Pavia, Italy
| | - Nina Feddermann-Demont
- Department of Neurology, University of Zurich, Zurich, Switzerland.,Clinical Neuroscience Center, University Hospital of Zürich, Zurich, Switzerland.,Swiss Concussion Center, Zurich, Switzerland
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Kim TS, Lim HW, Yang CJ, Kim YH, Choi WR, Kim YR, Park JW, Kang BC, Park HJ. Changes of video head impulse test results in lateral semicircular canal plane by different peak head velocities in patients with vestibular neuritis. Acta Otolaryngol 2018; 138:785-789. [PMID: 30016899 DOI: 10.1080/00016489.2018.1481523] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
BACKGROUND The peak head velocity influences on the video head impulse test (vHIT) results, but it has been not known how much the difference is. AIMS To evaluate the clinical evidence for the superiority of high-velocity compared to low-velocity vHIT. MATERIAL AND METHODS vHIT was performed in 30 patients with vestibular neuritis using two peak head velocities (mean 80 vs. 240°/s). vHIT gains and parameters of corrective saccades (CSs) were compared. A vHIT gain of ≤0.8 or a peak CS velocity of ≥100°/s was considered pathologic. RESULTS The vHIT gains were significantly lower (mean 0.5 vs. 0.6), and GA was larger (35 vs. 25%) at high-velocity vHIT, compared to low-velocity vHIT. CSs were significantly more frequent (100 vs. 80%) and peak CS velocities were larger (252 vs. 112°/s) at high-velocity vHIT. The abnormal rates based on vHIT gains were higher (90% vs. 73%) and CSs occurred more frequently (100% vs. 80%) at high-velocity vHIT. The abnormal rates based on the peak CS velocity were significantly higher at high-velocity vHIT (100% vs. 57%). CONCLUSION High-velocity vHIT is superior to low-velocity vHIT with a difference of 17-20% based on pathologic vHIT gains and presence of CSs.
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Affiliation(s)
- Tae Su Kim
- Department of Otolaryngology, Kangwon National University, Chuncheon, Republic of Korea
| | - Hyun Woo Lim
- Department of Otolaryngology, Asan Medical Center, Gangneung Asan Hospital, University of Ulsan College of Medicine, Gangneung, Republic of Korea
| | - Chan Joo Yang
- Department of Otorhinolaryngology-Head and Neck Surgery, Hanil General Hospital, Seoul, Republic of Korea
| | - Yong Han Kim
- Department of Otolaryngology-Head and Neck Surgery, Asan Medical Center, University of Ulsan, Seoul, Republic of Korea
| | - Woo Ri Choi
- Department of Otolaryngology-Head and Neck Surgery, Asan Medical Center, University of Ulsan, Seoul, Republic of Korea
| | - Yeh Ree Kim
- Department of Otolaryngology-Head and Neck Surgery, Asan Medical Center, University of Ulsan, Seoul, Republic of Korea
| | - Jun Woo Park
- Department of Otolaryngology-Head and Neck Surgery, Asan Medical Center, University of Ulsan, Seoul, Republic of Korea
| | - Byung Chul Kang
- Department of Otorhinolaryngology-Head and Neck Surgery, Ulsan University Hospital, Ulsan, Republic of Korea
| | - Hong Ju Park
- Department of Otolaryngology-Head and Neck Surgery, Asan Medical Center, University of Ulsan, Seoul, Republic of Korea
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Yang CJ, Cha EH, Park JW, Kang BC, Yoo MH, Kang WS, Ahn JH, Chung JW, Park HJ. Diagnostic Value of Gains and Corrective Saccades in Video Head Impulse Test in Vestibular Neuritis. Otolaryngol Head Neck Surg 2018; 159:347-353. [PMID: 29631490 DOI: 10.1177/0194599818768218] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Objectives We investigated changes in video head impulse test (vHIT) gains and corrective saccades (CSs) at the acute and follow-up stages of vestibular neuritis to assess the diagnostic value of vHIT. Study Design Case series with chart review. Setting Tertiary medical center. Subjects and Methods Sixty-three patients with vestibular neuritis who underwent vHIT at an initial presentation and an approximately 1-month follow-up were included. vHIT gains, gain asymmetry (GA), peak velocities of CS, and interaural difference of CS (CSD) were analyzed. Results Mean vHIT gains increased significantly from the acute stage to the follow-up exam. The mean GA, peak velocities of CS, and CSD had decreased significantly at the follow-up. The incidence of CSs was also significantly decreased at the follow-up. The abnormal rate (87%) considering both gain and CS value was significantly higher than that (62%) considering vHIT gain only at the follow-up, although the abnormal rates did not differ at the acute stage (97% vs 87%). Conclusion The abnormal rates based on both vHIT gains and CS measurements are similar at the acute stage of VN but are considerably higher at the follow-up stage compared with the abnormal rates based on vHIT gains alone. It is thus advisable to check both CS and vHIT gain while performing vHIT to detect vestibular hypofunction.
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Affiliation(s)
- Chan Joo Yang
- 1 Department of Otolaryngology, Hanil General Hospital, Seoul, Korea
| | - Eun Hye Cha
- 2 Department of Otolaryngology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
| | - Jun Woo Park
- 2 Department of Otolaryngology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
| | - Byung Chul Kang
- 2 Department of Otolaryngology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
| | - Myung Hoon Yoo
- 3 Department of Otolaryngology, College of Medicine, Kyungpook National University, Daegu, Korea
| | - Woo Suk Kang
- 2 Department of Otolaryngology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
| | - Joong Ho Ahn
- 2 Department of Otolaryngology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
| | - Jong Woo Chung
- 2 Department of Otolaryngology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
| | - Hong Ju Park
- 2 Department of Otolaryngology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
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Colagiorgio P, Versino M, Colnaghi S, Quaglieri S, Manfrin M, Zamaro E, Mantokoudis G, Zee DS, Ramat S. New insights into vestibular-saccade interaction based on covert corrective saccades in patients with unilateral vestibular deficits. J Neurophysiol 2017; 117:2324-2338. [PMID: 28404827 DOI: 10.1152/jn.00864.2016] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Revised: 04/10/2017] [Accepted: 04/10/2017] [Indexed: 11/22/2022] Open
Abstract
In response to passive high-acceleration head impulses, patients with low vestibulo-ocular reflex (VOR) gains often produce covert (executed while the head is still moving) corrective saccades in the direction of deficient slow phases. Here we examined 23 patients using passive, and 9 also active, head impulses with acute (< 10 days from onset) unilateral vestibular neuritis and low VOR gains. We found that when corrective saccades are larger than 10°, the slow-phase component of the VOR is inhibited, even though inhibition increases further the time to reacquire the fixation target. We also found that 1) saccades are faster and more accurate if the residual VOR gain is higher, 2) saccades also compensate for the head displacement that occurs during the saccade, and 3) the amplitude-peak velocity relationship of the larger corrective saccades deviates from that of head-fixed saccades of the same size. We propose a mathematical model to account for these findings hypothesizing that covert saccades are driven by a desired gaze position signal based on a prediction of head displacement using vestibular and extravestibular signals, covert saccades are controlled by a gaze feedback loop, and the VOR command is modulated according to predicted saccade amplitude. A central and novel feature of the model is that the brain develops two separate estimates of head rotation, one for generating saccades while the head is moving and the other for generating slow phases. Furthermore, while the model was developed for gaze-stabilizing behavior during passively induced head impulses, it also simulates both active gaze-stabilizing and active gaze-shifting eye movements.NEW & NOTEWORTHY During active or passive head impulses while fixating stationary targets, low vestibulo-ocular gain subjects produce corrective saccades when the head is still moving. The mechanisms driving these covert saccades are poorly understood. We propose a mathematical model showing that the brain develops two separate estimates of head rotation: a lower level one, presumably in the vestibular nuclei, used to generate the slow-phase component of the response, and a higher level one, within a gaze feedback loop, used to drive corrective saccades.
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Affiliation(s)
- Paolo Colagiorgio
- Department of Electrical, Computer and Biomedical Engineering, University of Pavia, Pavia, Italy
| | - Maurizio Versino
- Department of Brain and Behavioral Sciences, University of Pavia, Pavia, Italy.,Laboratory of Neuro-otology and Neuro-ophthalmology, C. Mondino National Neurological Institute, Pavia, Italy
| | - Silvia Colnaghi
- Department of Public Health, Experimental and Forensic Medicine, University of Pavia, Pavia, Italy.,Inter-Department Multiple Sclerosis Research Centre, C. Mondino National Neurological Institute, Pavia, Italy
| | - Silvia Quaglieri
- UOC Otorinolaringoiatria, Fondazione IRCCS San Matteo and University of Pavia, Pavia, Italy
| | - Marco Manfrin
- UOC Otorinolaringoiatria, Fondazione IRCCS San Matteo and University of Pavia, Pavia, Italy
| | - Ewa Zamaro
- Department of Otorhinolaryngology, Head and Neck Surgery, lnselspital, Bern University Hospital, University of Bern, Bern, Switzerland; and
| | - Georgios Mantokoudis
- Department of Otorhinolaryngology, Head and Neck Surgery, lnselspital, Bern University Hospital, University of Bern, Bern, Switzerland; and
| | - David S Zee
- Department of Neurology, Otolaryngology-Head and Neck Surgery, Neuroscience, Ophthalmology, Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - Stefano Ramat
- Department of Electrical, Computer and Biomedical Engineering, University of Pavia, Pavia, Italy;
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Anson ER, Bigelow RT, Carey JP, Xue QL, Studenski S, Schubert MC, Weber KP, Agrawal Y. Aging Increases Compensatory Saccade Amplitude in the Video Head Impulse Test. Front Neurol 2016; 7:113. [PMID: 27486430 PMCID: PMC4947583 DOI: 10.3389/fneur.2016.00113] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2016] [Accepted: 07/05/2016] [Indexed: 11/16/2022] Open
Abstract
Objective Rotational vestibular function declines with age resulting in saccades as a compensatory mechanism to improve impaired gaze stability. Small reductions in rotational vestibulo-ocular reflex (VOR) gain that would be considered clinically normal have been associated with compensatory saccades. We evaluated whether compensatory saccade characteristics varied as a function of age, independent of semicircular canal function as quantified by VOR gain. Methods Horizontal VOR gain was measured in 243 participants age 27–93 from the Baltimore Longitudinal Study of Aging using video head impulse testing. Latency and amplitude of the first saccade (either covert – occurring during head impulse, or overt – occurring following head impulse) were measured for head impulses with compensatory saccades (n = 2230 head impulses). The relationship between age and saccade latency, as well as the relationship between age and saccade amplitude, were evaluated using regression analyses adjusting for VOR gain, gender, and race. Results Older adults (mean age 75.9) made significantly larger compensatory saccades relative to younger adults (mean age 45.0). In analyses adjusted for VOR gain, there was a significant association between age and amplitude of the first compensatory covert saccade (β = 0.015, p = 0.008). In analyses adjusted for VOR gain, there was a significant association between age and amplitude of the first compensatory overt saccade (β = 0.02, p < 0.001). Compensatory saccade latencies did not vary significantly by age. Conclusion We observed that aging increases the compensatory catch-up saccade amplitude in healthy adults after controlling for VOR gain. Size of compensatory saccades may be useful in addition to VOR gain for characterizing vestibular function in aging adults.
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Affiliation(s)
- Eric R Anson
- Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine , Baltimore, MD , USA
| | - Robin T Bigelow
- Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine , Baltimore, MD , USA
| | - John P Carey
- Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine , Baltimore, MD , USA
| | - Quan-Li Xue
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA; Center on Aging and Health, Johns Hopkins Medical Institutions, Baltimore, MD, USA
| | - Stephanie Studenski
- Longitudinal Studies Section, National Institute on Aging , Baltimore, MD , USA
| | - Michael C Schubert
- Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine , Baltimore, MD , USA
| | - Konrad P Weber
- Department of Neurology, University Hospital Zurich, University of Zurich, Zurich, Switzerland; Department of Ophthalmology, University Hospital Zurich, University of Zurich, Zurich, Switzerland
| | - Yuri Agrawal
- Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine , Baltimore, MD , USA
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Kessler P, Zarandy MM, Hajioff D, Tomlinson D, Ranalli P, Rutka J. The clinical utility of search coil horizontal vestibulo-ocular reflex testing. Acta Otolaryngol 2008; 128:29-37. [PMID: 17851913 DOI: 10.1080/00016480701299642] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
CONCLUSION Testing of the horizontal vestibulo-ocular reflex (VOR) with head rotations (including head impulses) using the magnetic scleral search coil technique (SCT HHI) provides valuable additional diagnostic information in patients with persistent dizziness, oscillopsia or imbalance. It identifies high and low frequency/acceleration vestibular abnormalities that are frequently missed using other methods. OBJECTIVES To evaluate the diagnostic utility of SCT measurement of the horizontal VOR in the multidisciplinary neurotology clinic of a tertiary referral centre. PATIENTS AND METHODS The records of 127 consecutive patients referred for persistent dizziness, oscillopsia, imbalance, or with clinical findings suggestive of high frequency/acceleration vestibular dysfunction were reviewed. All had been tested with clinical head impulses, bithermal calorics and vestibular-evoked myogenic potentials. VOR gain (peak eye velocity/peak head velocity) had been measured both in response to sinusoidal oscillations in a rotating chair (0.1-11 Hz) and to manually delivered horizontal head rotations (peak head velocities 50-500 degrees/s) using SCT. RESULTS Agreement between the different test modalities of horizontal semicircular canal function was moderate. Relative to SCT HHI, clinical HHI showed the highest sensitivity and the lowest specificity (both 70%). SCT HHI appeared to have the greatest diagnostic yield, when compared with calorics and SCT ROT (23% of all abnormalities shown were detected only by SCT HHI) and also allowed detection of significant asymmetries in patients with bilateral vestibular dysfunction.
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Affiliation(s)
- Paul Kessler
- Otoneurology Laboratory, University Health Network, University of Toronto, Toronto, Ontario, Canada
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Wu Y, Yu Y, Kovács SJ. Contraction-relaxation coupling mechanism characterization in the thermodynamic phase plane: normal vs. impaired left ventricular ejection fraction. J Appl Physiol (1985) 2007; 102:1367-73. [PMID: 17185496 DOI: 10.1152/japplphysiol.00593.2006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Using simultaneous pressure-volume measurements obtained during cardiac catheterization, we employ the thermodynamic phase-plane (TPP) method to characterize global contraction-relaxation coupling (CRC) between normal and impaired left ventricular (LV) ejection fraction (LVEF) groups. The cardiac cycle inscribes a closed loop in the TPP defined by the coordinates “potential” power [V(dP/d t), ergs/s] and “kinetic” power [P(dV/d t), ergs/s]. The TPP-derived indexes κ and ρ define the chamber's contractile and CRC attributes, respectively. Data from 33 subjects dichotomized as normal control ( n = 22, >50% LVEF) and impaired LVEF ( n = 11, <50% LVEF) were analyzed. The results were as follows: κ = 3.0 ± 1.1 and ρ = −0.38 ± 0.21 for controls and κ = 5.4 ± 1.6 and ρ = −1.14 ± 0.47 for the impaired LVEF group; κ and ρ are significantly higher for impaired LVEF than for control ( P < 0.001 for both). As κ increased, ρ decreased ( r = −0.69) for all subjects. Hence, ventricles with impaired LVEF are thermodynamically less efficient because they require more potential power per unit of delivered kinetic power than controls. We conclude that TPP-derived indexes of CRC facilitate assessment of chamber efficiency in thermodynamic terms and elucidate the dominant differentiating features in terms of CRC indexes.
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Affiliation(s)
- Yue Wu
- Cardiovascular Biophysics Laboratory, Washington Univ. Medical Center, St. Louis, MO 63110, USA
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Migliaccio AA, Della Santina CC, Carey JP, Minor LB, Zee DS. The effect of binocular eye position and head rotation plane on the human torsional vestibuloocular reflex. Vision Res 2006; 46:2475-86. [PMID: 16545855 DOI: 10.1016/j.visres.2006.02.008] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2005] [Revised: 02/03/2006] [Accepted: 02/06/2006] [Indexed: 11/16/2022]
Abstract
We examined how the gain of the torsional vestibulo-ocular reflex (VOR) (defined as the instantaneous eye velocity divided by inverted head velocity) in normal humans is affected by eye position, target distance, and the plane of head rotation. In six normal subjects we measured three-dimensional (3D) eye and head rotation axes using scleral search coils, and 6D head position using a magnetic angular and linear position measurement device, during low-amplitude (approximately 20 degrees ), high-velocity (approximately 200 degrees/s), high-acceleration (approximately 4000 degrees /s2) rapid head rotations or 'impulses.' Head impulses were imposed manually and delivered in five planes: yaw (horizontal canal plane), pitch, roll, left anterior-right posterior canal plane (LARP), and right anterior-left posterior canal plane (RALP). Subjects were instructed to fix on one of six targets at eye level. Targets were either straight-ahead, 20 degrees left or 20 degrees right from midline, at distance 15 or 124 cm from the subject. Two subjects also looked at more eccentric targets, 30 degrees left or 30 degrees right from midline. We found that the vertical and horizontal VOR gains increased with the proximity of the target to the subject. Previous studies suggest that the torsional VOR gain should decrease with target proximity. We found, however, that the torsional VOR gain did not change for all planes of head rotation and for both target distances. We also found a dynamic misalignment of the vertical positions of the eyes during the torsional VOR, which was greatest during near viewing with symmetric convergence. This dynamic vertical skew during the torsional VOR arises, in part, because when the eyes are converged, the optical axes are not parallel to the naso-occipital axes around which the eyes are rotating. In five of six subjects, the average skew ranged 0.9 degrees -2.9 degrees and was reduced to <0.4 degrees by a 'torsional' quick-phase (around the naso-occipital axis) occurring <110 ms after the onset of the impulse. We propose that the torsional quick-phase mechanism during the torsional VOR could serve at least three functions: (1) resetting the retinal meridians closer to their usual orientation in the head, (2) correcting for the 'skew' deviation created by misalignment between the axes around which the eyes are rotating and the line of sight, and (3) taking the eyes back toward Listing's plane.
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Affiliation(s)
- Americo A Migliaccio
- Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University, MA 21205, USA.
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Peng GCY, Minor LB, Zee DS. Gaze Position Corrective Eye Movements in Normal Subjects and in Patients with Vestibular Deficits. Ann N Y Acad Sci 2006; 1039:337-48. [PMID: 15826987 DOI: 10.1196/annals.1325.032] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Eye movements in response to high-acceleration head rotations (thrusts) in the horizontal plane from patients with unilateral (UVD) or bilateral vestibular loss (BVD) were recorded. The rapid, gaze-position corrections (GPCs) that appeared when vestibulo-ocular reflex (VOR) slow phases were undercompensatory were characterized. For comparison, eye movements from normal subjects who were asked to generate saccades in the direction opposite head rotation (in the same direction as slow phases) were recorded. This normal-subject model produced responses with spatial and temporal characteristics similar to those from GPCs in patients as follows: When head rotations were generated actively, compared with passively, gaze-position errors and corresponding GPCs were smaller and occurred earlier. During passively generated head thrusts, GPCs still occurred when head rotations were made in total darkness, though their accuracy decreased as the requirement for maintaining gaze on a specific location in space was relaxed. Time of onset of GPCs was not rigidly tied to head kinematics (peak velocity or peak acceleration). Speeds of GPCs, however, were lower than speeds of similar-sized, head-fixed saccades. Finally, during passive and active head thrusts in patients, sustained, high-frequency (20 to 30 Hz) oscillations that appeared as tiny saccades were occasionally observed, one immediately following the other, resembling a compensatory slow-phase response. Taken together, the results suggest that one strategy for overcoming a VOR deficit is to enlist the saccadic system to produce an oculomotor response that is required to compensate for head rotation. This response may come in the form of high-velocity GPCs or smaller-amplitude oscillations.
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Affiliation(s)
- Grace C Y Peng
- Department of Neurology, The Johns Hopkins University, Pathology 2-210, 600 N. Wolfe Street, Baltimore, MD 21287-6921, USA
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Walker MF, Zee DS. Cerebellar Disease Alters the Axis of the High-Acceleration Vestibuloocular Reflex. J Neurophysiol 2005; 94:3417-29. [PMID: 16033941 DOI: 10.1152/jn.00375.2005] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
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.
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Affiliation(s)
- Mark F Walker
- Dept. of Neurology, The Johns Hopkins University, 600 N. Wolfe St., Pathology 2-210, Baltimore, MD 21287, USA.
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Ramat S, Straumann D, Zee DS. Interaural Translational VOR: Suppression, Enhancement, and Cognitive Control. J Neurophysiol 2005; 94:2391-402. [PMID: 15901755 DOI: 10.1152/jn.01328.2004] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We investigated the influence of cognitive factors on the early response of the interaural translational vestibuloocular reflex (tVOR) in six normal subjects. Variables were prior knowledge of direction of head motion and the position of the fixation target relative to the head [head-fixed (HF) or space-fixed (SF)]. A manually driven device provided a step-like head translation (∼35 mm distance, peak acceleration, 0.6–1.3 g). Subjects looked at the SF or HF target located 15 cm in front of their heads in otherwise complete darkness. The testing paradigms were: random interleaving of SF and HF targets with unknown direction of head movement, known target location with random head direction (SFR or HFR), and known target location with known head direction (SFP or HFP). Timing was always unpredictable. A “gain” of the slow phase was calculated with respect to ideal performance (maintained fixation of the SF target, recorded/ideal eye velocity computed at time of peak head velocity). At such times, there were no significant differences in gain between HF and SF trials in the random condition; the average gain was ∼36% of ideal. On the other hand, responses in the SFR and HFR conditions differed as early as 20 ms after the head began moving. Average gain was higher (0.43 ± 0.11 vs. 0.34 ± 0.14; means ± SD, P < 0.05) for each subject in the SFR than the HFR condition. For SFP and HFP, the responses differed from the onset of head motion. Average slow-phase gain was higher (0.49 ± 0.12 vs. 0.31 ± 0.12, P < 0.02) for each subject in SFP than in HFP. The timing of corrective saccades during the tVOR was also influenced by cognitive factors. Visual error signals seemed to be more important for triggering saccades in HF trials, whereas preprogramming, probably based on labyrinthine information, seemed to be more important in SF trials. Simulations showed that the changes in slow-phase gain with cognition could be reproduced with simple parametric adjustments of the gain of activity from otolith afferents and suggest that higher-level cognitive control of the VOR could occur as early as the synapse of peripheral afferents on neurons in the vestibular nuclei, either directly from higher level centers or via the cerebellum. In sum, the tVOR—both in its slow-phase response and the saccadic corrections—is subject to “higher-level” cognitive influences including knowledge of where the line of sight must point during head motion and the impending direction of head motion.
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Affiliation(s)
- Stefano Ramat
- Department of Neurology, The Johns Hopkins University, School of Medicine, Baltimore, MD 21231, USA.
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