Journal of Vestibular Research - Volume 9, issue 1

Authors: Clément, Gilles | Wood, Scott J. | Lathan, Corinna E. | Peterka, Robert J. | Reschke, Millard F.

Article Type: Research Article

Abstract: Spatial transformations of the vestibular-optokinetic system must account for changes in head position with respect to gravity in order to produce compensatory oculomotor responses. The purpose of this experiment was to study the influence of gravity on the vestibulo-ocular reflex (VOR) in darkness and on visual-vestibular interaction in the pitch plane in human subjects using two different comparisons: (1) Earth-horizontal axis (EHA) rotation about an upright versus a supine body orientation, and (2) Earth-horizontal versus Earth-vertical (EVA) rotation axes. Visual-vestibular responses (VVR) were evaluated by measuring the slow phase velocity of nystagmus induced during sinusoidal motion of the body in …the pitch plane (at 0.2 Hz and 0.8 Hz) combined with a constant-velocity vertical optokinetic stimulation (at ±36°/s). The results showed no significant effect on the gain or phase of the VOR in darkness or on the VVR responses at 0.8 Hz between EHA upright and EHA supine body orientations. However, there was a downward shift in the VOR bias in darkness in the supine orientation. There were systematic changes in VOR and VVR between EHA and EVA for 0.2 Hz, including a reduced modulation gain, increased phase lead, and decreased bias during EVA rotation. The same trend was also observed at 0.8 Hz, but at a lesser extent, presumably due to the effects of eccentric rotation in our EVA condition and/or to the different canal input across frequencies. The change in the bias at 0.2 Hz between rotation in darkness and rotation with an optokinetic stimulus was greater than the optokinetic responses without rotation. During EHA, changes in head position relative to gravity preserve graviceptor input to the VVR regardless of body orientation. However, the modifications in VVR gain and phase when the rotation axis is aligned with gravity indicate that this graviceptive information is important for providing compensatory eye movements during visual-vestibular interaction in the pitch plane. Show more

Keywords: vestibulo-ocular reflex, optokinetic nystagmus, visual-vestibular interaction, otoliths

DOI: 10.3233/VES-1999-9101

Citation: Journal of Vestibular Research, vol. 9, no. 1, pp. 1-11, 1999

Authors: Sondag, H.N.P.M. | de Jong, H.A.A. | Oosterveld, W.J.

Article Type: Research Article

Abstract: We studied vestibular function in 20 adult hamsters (3 months old) subjected to either prolonged hypergravity (n=10) or normal gravity (n=10) for 2 months. Locomotion and swimming of the hypergravity hamsters under light conditions were normal. Equilibrium maintenance was severely disturbed; only 6 of 10 hypergravity hamsters managed to walk on the small tube after 2 months, whereas all 10 controls were able to walk on the tube. The air-righting reflex was severely disturbed; the hypergravity hamsters made 30% correct responses. Finally, 5 of 8 hypergravity hamsters had to be saved from drowning when swimming in total darkness. Histological examination …of the utricular otoconial layers afterwards, using energy dispersive X-ray element (EDAX) analysis and scanning electron microscopy, did not reveal any differences in calcium content, shape and size distribution of the otoconia between hypergravity hamsters and controls. We suggest that adult hamsters adapt to hypergravity, leading to problems in normal functioning when tested in 1 G, especially in tasks in which sensory input of the vestibular system is important for spatial orientation. These disturbances were more severe in adult hamsters than in young ones, tested in previous experiments. Therefore, we assume that age is a factor for adaptation to altered gravity conditions. Show more

Keywords: balancing, air-righting reflex, swimming, otoconia

DOI: 10.3233/VES-1999-9102

Citation: Journal of Vestibular Research, vol. 9, no. 1, pp. 13-18, 1999

Authors: Pyykkö, Ilmari | Eklund, Susanna | Ishizaki, Hisayoshi | Aalto, Heikki

Article Type: Research Article

Abstract: We have treated 93 patients with severe Meniere's disease with gentamicin (GM) applied with 1 to 4 or intratympanic injections in a prospective study. The patients were tested at frequent intervals and followed up for two years. Postural stability was evaluated on posturography. Unsteadiness and gait between attacks, working capacity and vertigo were scored. Before commencing the treatment 47 of the patients complained from moderate to severe postural instability. After treatment moderate to severe postural instability was met in 19 patients. Initially the sway velocity was 27 mm/s on average being significantly worse than in referents. Two weeks after treatment …the sway velocity increased to 33 mm/s. Thereafter the sway velocity slowly started to decline to 31 mm/s after two years. Patients with severe attacks of rotatory vertigo had a good postural outcome with GM treatment. In logistic regression analysis the most significant risk factor for poor recovery after GM treatment was severely reduced gait before commencing the treatment with odds ratio of 2.0. Subjectively, after two years, the patients rated their postural stability significantly improved when compared to pretreatment values. The good subjective rating of postural stability is related to postural training program where in the absence of attacks, the patients have learned to cope with daily tasks. Show more

Keywords: meniere's disease, postural stability, gait disorders, vertigo, handicap

DOI: 10.3233/VES-1999-9103

Citation: Journal of Vestibular Research, vol. 9, no. 1, pp. 19-26, 1999

Authors: Groen, Eric | Bos, Jelte E. | de Graaf, Bernd

Article Type: Research Article

Abstract: The dynamic contribution of the otolith organs to the human ocular torsion response was examined during passive sinusoidal body roll about an earth-horizontal axis (varying otolith inputs) and about an earth-vertical axis (invariant otolith inputs). Torsional eye movements were registered in 5 subjects by means of video-oculography. At a fixed amplitude of 25°, the stimulus frequency was varied from 0.05 to 0.4 Hz. Additionally, at a fixed frequency of 0.2 Hz, the response was also measured at the amplitudes of 12.5° and 50°. The results showed that the gain and phase of the torsional slow component velocity (SCV) did not …depend on stimulus amplitude, indicating a linear response. Contribution of the otoliths affected the ocular torsion response in three different ways. First, the gain of the SCV was slightly, but consistently, higher during rotation about an earth-horizontal axis than during rotation about an earth-vertical axis. With invariant otolith inputs the average gain increased from 0.10 at 0.05 Hz to 0.26 at 0.25 Hz. With varying otolith inputs, the average gain increased from 0.14 to 0.37. Second and more substantially, contribution of the otoliths improved the response dynamics by reducing the phase lead at frequencies up to 0.2 Hz. Third, the nystagmus showed considerably less anticompensatory saccades in upright conditions than in supine conditions, even though the SCV gain was lower in the latter. As a consequence, the average excursion of torsional eye position was highest during earth-horizontal rotation. This effect was observed in the entire frequency range. Thus, the otoliths controlled the human torsional VOR not only at low stimulus frequencies by keeping the slow component in phase with head motion, but also in a wider frequency range by modulating the saccadic behavior as to increase the amplitude of ocular torsion. We conclude that the primary concern of the otolith-oculomotor system during head tilt is to stabilize eye position in space, rather than to prevent retinal blur. Show more

Keywords: ocular torsion, otoliths, saccades, nystagmus, VOR

DOI: 10.3233/VES-1999-9104

Citation: Journal of Vestibular Research, vol. 9, no. 1, pp. 27-36, 1999

Authors: Péruch, Patrick | Borel, Liliane | Gaunet, Florence | Thinus-Blanc, Gatherine | Magnan, Jacques | Lacour, Michel

Article Type: Research Article

Abstract: The purpose of this study was to investigate the effects of unilateral vestibular neurotomy on humans ability to perform navigation tasks. These tasks provided self-motion feedback by way of either locomotor activity only (nonvisual navigation or “locomotor task”) or visual motion cues only (visually simulated navigation or “visual task”). After exploration of an environment in which 4 locations were marked by different objects, subjects attempted to navigate to those locations either by reproducing the same paths as those followed during exploration, by reversing routes, or by making spatial inferences (shortcuts). Vestibular defective patients were tested one day before surgical treatment …and during the recovery time course following unilateral vestibular nerve lesion (1 week, 1 month, and 3 months later). Their performance was assessed by measuring turn error and distance error in both navigation tasks and was compared to that of control subjects tested 4 times at similar time intervals. Turn error in the reproduction of previously explored routes in the locomotor task was lower in patients before surgery than in controls, suggesting the existence of compensatory processes. In the acute stage (1 week) after unilateral vestibular lesion, turn error was greater in patients than in controls for the highest level of mental representation (spatial inferences or reversing routes); impairment at making accurate rotations had disappeared by 1 month after vestibular lesion in both navigation tasks. These results point to the role of vestibular cues, in interaction with other sensory modalities, in the elaboraion of an accurate internal representation of the environment. In addition, they suggest that unilateral suppression of vestibular information would induce transitory spatial memory disorganization at a high level of information processing. Show more

Keywords: unilateral vestibular disease, navigation, sensory modalities, compensation, human

DOI: 10.3233/VES-1999-9105

Citation: Journal of Vestibular Research, vol. 9, no. 1, pp. 37-47, 1999

Authors: Hillman, Edward J. | Bloomberg, Jacob J. | McDonald, P. Vernon | Cohen, Helen S.

Article Type: Research Article

Abstract: We describe a new, objective, easily administered test of dynamic visual acuity (DVA) while walking. Ten normal subjects and five patients with histories of severe bilateral vestibular dysfunction participated in this study. Subjects viewed a visual display of numerals of different font sizes presented on a laptop computer while they stood still and while they walked on a motorized treadmill. Treadmill speed was adapted for 4 of 5 patients. Subjects were asked to identify the numerals as they appeared on the computer screen. Test results were reasonably repeatable in normals. The percent correct responses at each font size dropped slightly …while walking in normals and dropped significantly more in patients. Patients performed significantly worse than normals while standing still and while walking. This task may be useful for evaluating post-flight astronauts and vestibularly impaired patients. Show more

Keywords: oscillopsia, walking, human, dynamic visual acuity

DOI: 10.3233/VES-1999-9106

Citation: Journal of Vestibular Research, vol. 9, no. 1, pp. 49-57, 1999

Authors: McDermott, Kate H. | Matheson, Anna J. | Titov, Nikoli | Darlington, Cynthia L. | Smith, Paul F.

Article Type: Research Article

Abstract: Previous studies have shown that experience with optokinetic stimulation can alter a subject's sensitivity to illusions such as circularvection (CV). The aim of the present experiment was to compare optokinetic nystagmus (OKN), optokinetic afternystagmus (OKAN), and sensitivity to CV between 2 groups of sportspeople: 1) squash players (n=16), who regularly experience vigorous optokinetic stimulation while engaging in their sporting activity, and 2) weightlifters (n=16), whose sport does not involve the same degree of optokinetic stimulation as squash, but who nevertheless have to achieve a high degree of physical skill. OKN, OKAN (frequency, slow phase velocity, and timeconstant), and latency to …CV (Stage 2 and Stage 3) were measured using electro-oculographic recording inside an optokinetic drum. Contrary to predictions,there were no significant differences in OKN, OKAN, or latency to CV between the 2 groups. These results suggest that 1) the practice effects that alter the sensitivity to CV may decay relatively quickly, and 2) differences in recreational sporting activities between subjects may not be a significant confounding factor in visual-vestibular interaction experiments. Show more

Keywords: optokinetic, circularvection, optokinetic nystagmus

DOI: 10.3233/VES-1999-9107

Citation: Journal of Vestibular Research, vol. 9, no. 1, pp. 59-61, 1999

Authors: Asmundson, Gordon J.G. | Stein, Murray B. | Ireland, Desmond

Article Type: Research Article

Abstract: Panic disorder and agoraphobia have been associated with increased functional disability in individuals who have vestibular problems. The Dizziness Handicap Inventory (DHI), a 25-item self-report questionnaire with three rationally derived subscales, was designed to measure functional, emotional, and physical disability associated with vestibular disturbance. Despite the apparent usefulness of the DHI, there have been few studies of its psychometric properties. The primary purpose of the present study was to assess the factor structure of the DHI. A principal components analysis with oblique rotation was conducted on data collected from 95 patients referred to a tertiary-care vestibular disorders clinic for assessment …of vestibular disturbance. Both 2-factor and 3-factor solutions are reported. The 2-factor solution was indicative of General Functional Limitations and Postural Difficulties. In the 3-factor solution, General Functional Limitations was split into factors indicative of Disability in Activities of Daily Living and Phobic Avoidance, while the Postural Difficulties factor remained stable. We also characterized the 3-factor solution by assessing the correlation of factor scores with measures of vestibular symptoms, mood, and anxiety. The general pattern of results does not support the validity of the original subscale structure of the DHI. Implications for revising the DHI to provide a more comprehensive and factorially valid assessment of disability associated with vestibular disturbance are discussed. Show more

Keywords: dizziness Handicap Inventory, phobic avoidance, factor analysis, vestibular disturbance

DOI: 10.3233/VES-1999-9108

Citation: Journal of Vestibular Research, vol. 9, no. 1, pp. 63-68, 1999