Journal of Vestibular Research - Volume 9, issue 3

Article Type: Obituary

DOI: 10.3233/VES-1999-9301

Citation: Journal of Vestibular Research, vol. 9, no. 3, pp. 155-155, 1999

Authors: Henn, Volker | Straumann, Dominik

Article Type: Research Article

Abstract: Methods to measure eye rotations in 3D have developed to a stage where routine clinical application is realistic. Besides the equipment, it requires a basic understanding of 3-dimensional geometry for calibration and interpretation. Relevant parameters are orientation, displacement and thickness of Listing's plane for spontaneous or goal-directed eye movements, and counterrolling or nystagmus with a roll component for vestibular function. The method with the highest temporal and spatial resolution is the magnetic search coil technique. Video-based systems are still slow and cannot be used to characterize saccades. Often, the task of reconstructing the 3-dimensional eye position from a 2-dimensional image …of the eye is underestimated. Search coil measurements have shown no firm correlation between the orientation of Listing's plane and “classical” landmarks like stereotaxic head position, emphasizing that Listing's plane is functionally, and not anatomically, determined. Show more

Keywords: listing's plane, magnetic search coils, torsion, primary position

DOI: 10.3233/VES-1999-9302

Citation: Journal of Vestibular Research, vol. 9, no. 3, pp. 157-162, 1999

Authors: Cohen, Bernard | Wearne, Susan | Dai, Mingjia | Raphan, Theodore

Article Type: Research Article

Abstract: During vestibular nystagmus, optokinetic nystagmus (OKN), and optokinetic afternystagmus (OKAN), the axis of eye rotation tends to align with the vector sum of linear accelerations acting on the head. This includes gravitational acceleration and the linear accelerations generated by translation and centrifugation. We define the summed vector of gravitational and linear accelerations as gravito-inertial acceleration (GIA) and designate the phenomenon of alignment as spatial orientation of the angular vestibuloocular reflex (aVOR). On the basis of studies in the monkey, we postulated that the spatial orientation of the aVOR is dependent on the slow (velocity storage) component of the aVOR, not …on the short latency, compensatory aVOR component, which is in head-fixed coordinates. Experiments in which velocity storage was abolished by midline medullary section support this postulate. The velocity storage component of the aVOR is likely to be generated in the vestibular nuclei, and its spatial orientation was shown to be controlled through the nodulus and uvula of the vestibulo-cerebellum. Separate regions of the nodulus/uvula appear to affect the horizontal and vertical/torsional components of the response differently. Velocity storage is weaker in humans than in monkeys, but responds in a similar fashion in both species. We postulate that spatial orientation of the aVOR plays an important role in aligning gaze with the GIA and in maintaining balance during angular locomotion. Show more

Keywords: spatial orientation, nystagmus, centrifugation, otolith, semicircular canals, velocity storage

DOI: 10.3233/VES-1999-9303

Citation: Journal of Vestibular Research, vol. 9, no. 3, pp. 163-172, 1999

Authors: Aw, S.T. | Halmagyi, G.M. | Black, R.A. | Curthoys, I.S. | Yavor, R.A. | Todd, M.J.

Article Type: Research Article

Abstract: We studied individual semicircular canal responses in three dimensions to high-acceleration head rotations (“head impulses”) in subjects with known surgical lesions of the semicircular canals, and compared their results to those of normal subjects. We found that vestibular-ocular reflex (VOR) gains at close to peak head velocity in response to yaw, pitch and roll impulses were reliable indicators of semicircular canal function. When compared to normals, lateral canal function showed a 70–80% gain at peak of yaw head velocity during ipsilesional yaw impulses. After the loss of one vertical canal function there was a 30–50% and torsional VOR gain in …response to ipsilesional pitch and roll impulses respectively. Bilateral deficits in anterior or posterior canal function resulted in a 80–90% impulses, while the loss of ipsilateral anterior and posterior canal functions will result in a 80–90% ipsilesional roll impulses. Three-dimensional vector analysis and animation of the VOR responses in a unilateral vestibular deafferented subject to yaw, pitch and roll impulses further demonstrated the deficits in magnitude and direction of the VOR responses following the loss of unilateral lateral, anterior and posterior canal functions. Show more

Keywords: vestibulo-ocular reflex, semicircular canals, head impulses, VOR gain

DOI: 10.3233/VES-1999-9304

Citation: Journal of Vestibular Research, vol. 9, no. 3, pp. 173-180, 1999

Authors: Fetter, Michael | Haslwanter, Thomas

Article Type: Research Article

Abstract: The eye muscles in humans are arranged such that they allow rotations of the globe about any axis in three-dimensional space. Only 3D analysis techniques will suffice to describe the sometimes complex dependencies between the elicited eye movements and the stimulation conditions. With the recent availability of modern 3D eye movement measurement techniques and the further development of appropriate mathematical descriptions, we are now able to study eye movements in all three degrees of freedom. This article describes the basic mathematical tools for 3D eye movement analysis like rotation vectors, reference frames, coordinate systems, and the concept of Listing's law. …In a second part some clinical applications are presented. The close coupling between the vestibular and the oculomotor system suggests that by observing spontaneous and elicited eye movements in the case of an acute unilateral vestibular pathology we might be able to find out which parts of the vestibular system (that is, which of the semicircular canals or which of the otoliths) are affected. The rationale of such an analysis is based on the observation that electrical stimulation of single semicircular canal afferents in animals induces eye movements that lie roughly in the plane of the canal. It is, therefore, possible to deduce which canals cause the eye movements observed when only some parts of the vestibular system are defective. Thus, the analysis of 3D movements not only provides an improved understanding of how the brain organizes movement in 3D space, but also has the potential to significantly improve our diagnostic capabilities. Show more

Keywords: three-dimensional eye movements, Listing's law, coordinate systems, vestibulo-ocular reflex

DOI: 10.3233/VES-1999-9305

Citation: Journal of Vestibular Research, vol. 9, no. 3, pp. 181-187, 1999

Authors: Furman, Joseph M. | Durrant, John D.

Article Type: Research Article

Abstract: Head-only rotational testing (HORT) is a method of assessing the vestibulo-ocular reflex (VOR) that can be performed at the bedside with inexpensive, transportable equipment. Previous studies of HORT using auditory cuing have suggested that test results are in large part independent of the method by which a subject's head is moved, that is, active versus passive. However, many subjects have difficulty moving their head at rotational frequencies of 3 Hz or greater. In an attempt to overcome this difficulty, and to learn more about HORT, we explored the possibility of providing subjects with a somatosensory, rather than an auditory cue …for head movement. Somatosensory, cues were provided either by applying gentle pressure against a tightly-fitted headband or by lightly tapping on the shoulders. Our results with young, healthy subjects indicate that somatosensory cuing is an efficacious means of inducing periodic head rotation and that HORT results are unaffected by the type of cue provided. We conclude that somatosensory rather than auditory cuing may be the preferred method of performing HORT. Show more

Keywords: vestibulo-ocular reflex, human, diagnostic testing, vision

DOI: 10.3233/VES-1999-9306

Citation: Journal of Vestibular Research, vol. 9, no. 3, pp. 189-195, 1999

Authors: Borger, L.L. | Whitney, S.L. | Redfern, M.S. | Furman, J.M.

Article Type: Research Article

Abstract: Postural sway during stance has been found to be sensitive to moving visual scenes in young adults, children, and those with vestibular disease. The effect of visual environments on balance in elderly individuals is relatively unknown. The purpose of this study was to compare postural sway responses of healthy elderly to those of young subjects when both groups were exposed to a moving visual scene. Peak to peak, root mean squared, and mean velocity of the center of pressure were analyzed under conditions combining four moving scene amplitudes (2 . 5 ∘ , 5 …∘ , 7 . 5 ∘ , 10 ∘ ) and two frequencies of scene movement (0.1 Hz, 0.25 Hz). Each visual condition was tested with a fixed floor and sway referenced platform. Results showed that elderly subjects swayed more than younger subjects when experiencing a moving visual scene under all conditions. The elderly were affected more than the young by sway referencing the platform. The differences between the two age groups were greater at increased amplitudes of scene movement. These results suggest that elderly are more influenced by dynamic visual information for balance than the young, particularly when cues from the ankles are altered. Show more

Keywords: postural sway, elderly, vision, proprioception

DOI: 10.3233/VES-1999-9307

Citation: Journal of Vestibular Research, vol. 9, no. 3, pp. 197-205, 1999

Authors: Clément, Gilles | Wood, Scott J. | Reschke, Millard F. | Berthoz, Alain | Igarashi, Makoto

Article Type: Research Article

Abstract: Both yaw and pitch visual-vestibular interactions at two separate frequencies of chair rotation (0.2 and 0.8 Hz) in combination with a single velocity of optokinetic stimulus (36 ∘ /s) were used to investigate the effects of sustained weightlessness on neural strategies adopted by astronaut subjects to cope with the stimulus rearrangement of spaceflight. Pitch and yaw oscillation in darkness at 0.2 and 0.8 Hz without optokinetic stimulation, and constant velocity linear optokinetic stimulation at 18, 36, and 54 ∘ /s presented relative to the head with the subject stationary, were …used as controls for the visual-vestibular interactions. The results following 8 days of space flight showed no significant changes in: (1) either the horizontal and vertical vestibulo-ocular reflex (VOR) gain, phase, or bias; (2) the yaw visual-vestibular response (VVR); or (3) the horizontal or vertical optokinetic (OKN) slow phase velocity (SPV). However, significant changes were observed: (1) when during pitch VVR at 0.2 Hz late inflight, the contribution of the optokinetic input to the combined oculomotor response was smaller than during the stationary OKN SPV measurements, followed by an increased contribution during the immediate postflight testing; and (2) when during pitch VVR at 0.8 Hz, the component of the combined oculomotor response due to the underlying vertical VOR was more efficiently suppressed early inflight and less suppressed immediately postflight compared with preflight observations. The larger OKN response during pitch VVR at 0.2 Hz and the better suppression of VOR during pitch VVR at 0.8 Hz postflight are presumably due to the increased role of vision early inflight and immediately after spaceflight, as previously observed in various studies. These results suggest that the subjects adopted a neural strategy to structure their spatial orientation in weightlessness by reweighting visual, otolith, and perhaps tactile/somatic signals. Show more

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

DOI: 10.3233/VES-1999-9308

Citation: Journal of Vestibular Research, vol. 9, no. 3, pp. 207-220, 1999

Authors: Hess, K.

Article Type: Book Review

DOI: 10.3233/VES-1999-9309

Citation: Journal of Vestibular Research, vol. 9, no. 3, pp. 221-221, 1999