Journal of Vestibular Research - Volume 8, issue 3

Authors: Nicholas, Spero C. | Doxey-Gasway, D.D. | Paloski, William H.

Article Type: Research Article

Abstract: Sensory-motor control of upright human posture may be organized in a top-down fashion such that certain head-trunk coordination strategies are employed to optimize visual and/or vestibular sensory inputs. Previous quantitative models of the biomechanics of human posture control have examined the simple case of ankle sway strategy, in which an inverted pendulum model is used, and the somewhat more complicated case of hip sway strategy, in which multisegment, articulated models are used. While these models can be used to quantify the gross dynamics of posture control, they are not sufficiently detailed to analyze head-trunk coordination strategies that may be crucial …to understanding its underlying mechanisms. In this paper, we present a biomechanical model of upright human posture that extends an existing four mass, sagittal plane, link-segment model to a five mass model including an independent head link. The new model was developed to analyze segmental body movements during dynamic posturography experiments in order to study head-trunk coordination strategies and their influence on sensory inputs to balance control. It was designed specifically to analyze data collected on the EquiTest™ (NeuroCom International, Clackamas, OR) computerized dynamic posturography system, where the task of maintaining postural equilibrium may be challenged under conditions in which the visual surround, support surface, or both are in motion. The performance of the model was tested by comparing its estimated ground reaction forces to those measured directly by support surface force transducers. We conclude that this model will be a valuable analytical tool in the search for mechanisms of balance control. Show more

Keywords: posture control, vestibular, biomechanical model, sensory-motor

DOI: 10.3233/VES-1998-8301

Citation: Journal of Vestibular Research, vol. 8, no. 3, pp. 187-200, 1998

Authors: Paul, C. Alice A.E. | Sansom, Andrew J. | Maclennan, Karyn | Darlington, Cynthia L. | Smith, Paul F.

Article Type: Research Article

Abstract: Recent studies have suggested that steroids such as dexamethasone and methylprednisolone might be useful in the treatment of vestibular disorders, irrespective of whether inflammatory processes are involved. The aim of this study was to investigate the effects of systemic administration of dexamethasone on vestibular compensation of spontaneous nystagmus (SN) in guinea pig, and the effects of dexamethasone and methylprednisolone on extracellularly recorded spontaneous activity of medial vestibular nucleus (MVN) neurons in brainstem slices in vitro. In the behavioral study, none of the 3 doses of dexamethasone (5, 10, or 40 mg/kg ip, delivered at 0, 12, 24, and 36 h …following a unilateral surgical labyrinthectomy (UL)) resulted in a significant change in the frequency or compensation of SN, relative to the vehicle control group. In the in vitro study, only a minority of MVN neurons showed any response to 1μM dexamethasone (lout of 9 neurons), or 10 nM (3 out of 13), or 0.1μM methylprednisolone (3 out of 7). These results suggest, contrary to previous evidence, that dexamethasone may not accelerate compensation of SN following surgical UL and that dexamethasone and methylprednisolone may have a direct action only on a minority of MVN neurons. Show more

Keywords: vestibular compensation, medial vestibular nucleus, vestibular disorders, steroids, methylprednisolone

DOI: 10.3233/VES-1998-8302

Citation: Journal of Vestibular Research, vol. 8, no. 3, pp. 201-207, 1998

Authors: Ogata, Yoichi | Slepecky, Norma B.

Article Type: Research Article

Abstract: This study demonstrates the presence of calmodulin in the vestibular end-organs of the gerbil by use of immunocytochemistry. Using fluorescence microscopy, calmodulin was localized to the cytoplasm, cuticular plate, and stereocilia of both type I and type II hair cells in the sensory epithelia of the utricle and cristae ampullaris; no label was found in the supporting cells, the dark cells, or the nerve fibers. There was no immunoreactive distinction between the labeling of type I and type II hair cells in the striolar or extrastriolar regions. Thus, immunocytochemical labeling for calmodulin provides a good marker for hair cells in …gerbil vestibular epithelium. The presence of calmodulin in the stereocilia was confirmed by immunoelectron microscopy using secondary antibodies coupled to colloidal gold. Show more

Keywords: calmodulin, vestibular hair cells, stereocilia, immunocytochemistry

DOI: 10.3233/VES-1998-8303

Citation: Journal of Vestibular Research, vol. 8, no. 3, pp. 209-216, 1998

Authors: Diamond, Shirley G. | Markham, Charles H.

Article Type: Research Article

Abstract: Three astronauts underwent preflight, inflight, and postflight testing of spontaneous ocular torsion and of ocular counterrolling (OCR), reflexes governed by the gravity-responsive otolith organs in the inner ear. One astronaut, A, had a 30-day space mission on Euromir '94 and was examined monocularly with SeusoMotoric Instruments video-oculography (VOG). The other two astronauts, B and C, were studied with a binocular VOG and flew an ISO-day mission on Euromir '95. In space, spontaneous eye torsion in the upright position was found to be substantially offset from baseline Earth-based recordings in all three subjects for the duration of the flights. In addition, …the binocular studies showed a marked torsional disconjugacy. On return to Earth, offset and torsional disconjugacy persisted for many days. OCR in response to 30° right and left tilt was examined preflight and postflight. Compared to preflight, Astronaut A showed reduced OCR immediately postflight, which increased over the next few days. Both Astronauts Band C had increased OCR postflight, which gradually approached but did not achieve the preflight values over 13 days postflight. The adaptation of ocular torsion in space in one astronaut and not in the other two, and slow adaptation postflight, may reflect the lack of visual feedback and the open loop nature of the otolith-ocular torsion reflex. Show more

Keywords: gravity, otoliths, ocular torsion, space

DOI: 10.3233/VES-1998-8304

Citation: Journal of Vestibular Research, vol. 8, no. 3, pp. 217-231, 1998

Authors: Nazareth, Andrea M. | Jones, Timothy A.

Article Type: Research Article

Abstract: Far-field recordings of short latency vestibular responses to pulsed cranial translation are composed of a series of positive and negative peaks occurring within 10 ms following stimulus onset. In the bird, these vestibular evoked potentials (VsEPs) can be recorded noninvasively and have been shown in the chicken and quail to depend strictly upon the activation of the vestibular component of the eighth nerve. The utility of the VsEP in the study of vestibular systems is dependent upon a clear understanding of the neural sources of response components. The primary aim of the current research in the chicken was to critically …test the hypotheses that 1) responses are generated by both peripheral and central neurons and 2) peaks P1 and N1 originate from first order vestibular neurons, whereas later waves primarily depend on activity in higher order neurons. The principal strategy used here was to surgically isolate the eighth nerve as it enters the brainstem. Interruption of primary afferents of the eighth nerve in the brainstem substantially reduced or eliminated peaks beyond P2, whereas PI and N1 were generally spared. Surgical sections that spared vestibular pathways had little effect on responses. The degree of change in response components beyond N1 was correlated with the extent of damage to central vestibular relays. These findings support the conclusion that responses are produced by both peripheral and central elements of the vestibular system. Further, response peaks later than N1 appear to be dependent upon central relays, whereas PI and N1 reflect activity of the peripheral nerve. These findings clarify the roles of peripheral and central neurons in the generation of vestibular evoked potentials and provide the basis for a more useful and detailed interpretation of data from vestibular response testing. Show more

Keywords: linear acceleration, neural generators, VsEP, vestibular response, bird, evoked potential

DOI: 10.3233/VES-1998-8305

Citation: Journal of Vestibular Research, vol. 8, no. 3, pp. 233-252, 1998

Authors: Jones, Timothy A. | Jones, Sherri M. | Colbert, Stephen

Article Type: Research Article

Abstract: Transient linear acceleration stimuli have been shown to elicit eighth nerve vestibular compound action potentials in birds and mammals. The present study was undertaken to better define the nature of the adequate stimulus for neurons generating the response in the chicken (Gallus domesticus). In particular, the study evaluated the question of whether the neurons studied are most sensitive to the maximum level of linear acceleration achieved or to the rate of change in acceleration (da/dt, or jerk). To do this, vestibular response thresholds were measured as a function of stimulus onset slope. Traditional computer signal averaging was used to record …responses to pulsed linear acceleration stimuli. Stimulus onset slope was systematically varied. Acceleration thresholds decreased with increasing stimulus onset slope (decreasing stimulus rise time). When stimuli were expressed in units of jerk (g/ms), thresholds were virtually constant for all stimulus rise times. Moreover, stimuli having identical jerk magnitudes but widely varying peak acceleration levels produced virtually identical responses. Vestibular response thresholds, latencies and amplitudes appear to be determined strictly by stimulus jerk magnitudes. Stimulus attributes such as peak acceleration or rise time alone do not provide sufficient information to predict response parameter quantities. Indeed, the major response parameters were shown to be virtually independent of peak acceleration levels or rise time when these stimulus features were isolated and considered separately. It is concluded that the neurons generating short latency vestibular evoked potentials do so as “jerk encoders” in the chicken. Primary afferents classified as “irregular”, and which traditionally fall into the broad category of “dynamic” or “phasic” neurons, would seem to be the most likely candidates for the neural generators of short latency vestibular compound action potentials. Show more

Keywords: macular velocity detection, jerk, jerk detection, linear jerk, birds, otolith, macula, pulsed acceleration, pulsed jerk, evoked potential, vestibular evoked potentials

DOI: 10.3233/VES-1998-8306

Citation: Journal of Vestibular Research, vol. 8, no. 3, pp. 253-272, 1998

Authors: Hanson, Jason M. | Goebel, Joel A.

Article Type: Research Article

Abstract: New methods of rotational testing of the vestibulo-ocular reflex (VOR) using manually generated or patient-generated sinusoidal head movements have recently been advocated for clinical use in circumstances where conventional rotary chair testing methods are not feasible. However, studies seeking to provide evidence for the validity of these methods by comparing their results with an accepted “gold-standard” have been conspicuously absent in the literature. In this study, we compared results for VOR gain, phase, and asymmetry obtained using whole-body and head-on-body rotational stimuli with those obtained by conventional rotary chair testing in 35 subjects with either unilateral or bilateral vestibular deficits …over the range of frequencies from 0.025 Hz to 1 Hz. Our results provide evidence for the validity of manual whole-body and active and passive head-on-body rotational testing methods by demonstrating excellent agreement between each of these and conventional rotational chair testing for VOR gain, phase, and asymmetry within the frequency range studied. Small differences at specific-paradigm datapoints are likely secondary to subtle limitations of our experimental design. With further refinement, we expect the new methods will be useful adjuncts for evaluating patients with vestibular complaints in selected clinical situations. Show more

Keywords: vestibulo-ocular reflex, rotational testing, headshake VOR, head-on-body rotation, methods

DOI: 10.3233/VES-1998-8307

Citation: Journal of Vestibular Research, vol. 8, no. 3, pp. 273-282, 1998