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doi: 10.3233/VES-2009-0355pmid: 20448334
Susceptibility to motion sickness was tested by exposing free moving toads to rotation of a stimulator modeled after an amusement park Ferris Wheel. The stimulator provided a gentle stimulation of frequency 0.25 Hz and centrifugal acceleration 0.143 g during 120 min or more without external visual cues. No emetic or prodromal behavioral response was elicited during or after rotation. During rotation the amount of motor activity in most toads increased evidently. The most active toads attempted to climb out of the test chamber. It was inferred that experimental rotation was rather a stressful stimulus which initiated an escape response. In addition, during rotation the number of eye retractions and urination incidences increased, but appetite after rotation was inhibited. During rotation the motionless toads performed small regular head movements with period equal to rotation period of stimulator. These oscillations were probably vestibular (otolith) reaction to oscillating acceleration. The proposed resonance hypothesis gives a general idea of why lower vertebrates are immune to motion sickness.
Fukasawa, Masahiko ; Okamoto, Kazuki ; Nakamura, Manabu ; Mikami, Koshi ; Shimada, Sonoko ; Tanaka, Yasuhiko ; Nagai, Kouhei ; Arito, Mitsumi ; Kurokawa, Manae S. ; Masuko, Kayo ; Suematsu, Naoya ; Koizuka, Izumi ; Kato, Tomohiro
doi: 10.3233/VES-2009-0356pmid: 20448335
Unilateral labyrinthectomy (UL) in rats is used as a human vertigo model. In this model, spontaneous nystagmus and dysequilibrium caused by UL are ameliorated within 48–72 hours. The amelioration, termed vestibular compensation (VC), is long lasting. Although cerebellar flocculi have been reported to be involved in VC, the molecular mechanisms behind VC are unknown. In this study, we used 2D-DIGE to detect protein changes in flocculi during acute (48 hours) and chronic (1 week) stages of VC. We found 99 out of 967 protein spots that showed significant changes in their intensities. Of the 99 spots, 45 spots (ipsilateral side, 15; contralateral side, 30) changed unilaterally during the acute stage, whereas 46 spots (ipsilateral side, 21; contralateral side, 25) changed unilaterally during the chronic stage. Thus, the acute compensation mechanism is more complicated in the contralateral flocculus than in the ipsilateral flocculus. Using MALDI-TOF MS, we identified 10 proteins out of the 12 protein spots. Of these, 3 proteins involved in synaptic transmission, neuronal filament formation and vesicular transport, respectively, demonstrated altered expression only in the acute stage. Our results enhance the understanding of the role of the cerebellar flocculi in VC generation.
Selva, Pierre ; Oman, Charles M. ; Stone, Howard A.
doi: 10.3233/VES-2009-0359pmid: 20448336
The mathematical model for the dynamics of the cupula-endolymph system of the inner ear semicircular canal, as elaborated by numerous investigators, remains a foundational tool in all of vestibular physiology. Most models represent the cupula as a linear spring-like element of stiffness K=ΔP/ΔV, where ΔV is the volume displaced upon application of a pressure difference ΔP. The parameter K directly influences the long time constant of the cupula-endolymph system. Given estimates of K based on experiments, we use thick and thin bending membrane theory, and also finite-element simulations based on more realistic cupula morphologies, to estimate the human cupula's Young's modulus E ≈ 5.4 Pa. We show that for a model morphology, thick bending membrane theory and finite-element predictions are in good agreement, and conclude that the morphology of the attachment of the cupula to the slope of the crista should not greatly influence the volume displacement. We note, however, that other biological materials with very low E are hydrogels that have significant viscoelastic properties. Experiments to directly measure E and investigate potential viscoelastic behavior ultimately may be needed. In addition, based on experimental images we study two other different shapes for the cupula and quantify their impact on the deflection of the cupula. We also use a three-dimensional finite-element model to analyze both the shear strain distribution and its time evolution near the sensory epithelium. We conclude that stimulation of sensory hair cells probably begins at the centre of the crista and spreads toward the periphery of the cupula and down the sides of the crista. Thus, spatio-temporal variations in the shearing stimulus are predicted to impact subsequent transduction and encoding. Finally, modeling the fluid-filled vertical channels believed to lie within the cupula, we investigate the impact of different tube diameters on the transverse displacement field. We show that, for the assumed diameters and grid spacing, cupula displacements should be highly sensitive to the diameter of the tubes. Experiments to verify the existence of cupular channels and accurately measure their diameter and spacing are needed.
Arthur, Joeanna C. ; Philbeck, John W. ; Chichka, David
doi: 10.3233/VES-2009-0354pmid: 20448337
Non-sensory (cognitive) inputs can play a powerful role in monitoring one's self-motion. Previously, we showed that access to spatial memory dramatically increases response precision in an angular self-motion updating task (1). Here, we examined whether spatial memory also enhances a particular type of self-motion updating – angular path integration. "Angular path integration" refers to the ability to maintain an estimate of self-location after a rotational displacement by integrating internally-generated (idiothetic) self-motion signals over time. It was hypothesized that remembered spatial frameworks derived from vision and spatial language should facilitate angular path integration by decreasing the uncertainty of self-location estimates. To test this we implemented a whole-body rotation paradigm with passive, non-visual body rotations (ranging 40°–140°) administered about the yaw axis. Prior to the rotations, visual previews (Experiment 1) and verbal descriptions (Experiment 2) of the surrounding environment were given to participants. Perceived angular displacement was assessed by open-loop pointing to the origin (0°). We found that within-subject response precision significantly increased when participants were provided a spatial context prior to whole-body rotations. The present study goes beyond our previous findings by first establishing that memory of the environment enhances the processing of idiothetic self-motion signals. Moreover, we show that knowledge of one's immediate environment, whether gained from direct visual perception or from indirect experience (i.e., spatial language), facilitates the integration of incoming self-motion signals.
Vanspauwen, R. ; Wuyts, F.L. ; Van de Heyning, P.H.
doi: 10.3233/VES-2009-0358pmid: 20448338
Objective: To determine normal limits and to analyse the test-retest reliability of the vestibular evoked myogenic potentials (VEMPs) parameters. Methods: The VEMP procedure was repeated on different test days to analyze test-retest differences. We calculated several reliability parameters: intraclass reliability coefficient (ICC), method error (ME), coefficient of variation of the method error (CV _{ME} ), standard error of measurement (SEM) and minimal difference (MD) for test-retest measurements. Normal values for left-right differences, based on the interaural ratio (IAR), were determined. Results: For each VEMP parameter, the ICC values indicated excellent reliability, except for p13 and corrected amplitude (fair to good reliability). The CV _{ME} values were less than 7% for p13, n23, threshold, MRV _{females} and MRV _{males} . For the parameters corrected amplitude and raw amplitude, the CV _{ME} values exceeded 15%. The 95% IAR prediction intervals (PIs) were also largest for the parameters raw amplitude and corrected amplitude. Conclusion: In order to evaluate a VEMP outcome in a patient, the VEMP parameters and IAR values can be compared with the 95% PI of the normal values. When successive measurements are performed within the same subjects, the minimal difference (MD) serves as a tool to decide whether these differences are clinically relevant or not.
Pal, Sudipto ; Rosengren, Sally M. ; Colebatch, James G.
doi: 10.3233/VES-2009-0360pmid: 20448339
We investigated the effects of bicathodal stochastic galvanic vestibular stimulation (GVS) on body sway in normal subjects and in Parkinson's Disease (PD) patients. Twenty normal subjects and five PD patients were stimulated with four stimulus intensities between 0 and 0.5 mA and sway was measured in two stance conditions (on a compliant surface with either eyes open (EOCS) or closed (ECCS)). Subjects stood facing forward with their feet together on a force platform. Centre of pressure (CoP) displacement over 26 seconds was measured in the anteroposterior (AP) and mediolateral (ML) planes. GVS had no significant overall effect on sway in the normal subjects. In the patients a small (4.5%) significant decrease in sway was seen in the ECCS condition with low intensity (0.1 mA) stimulation (P=0.02). Similar changes were seen in the normal subjects. This work indicates that low intensities of stochastic GVS can reduce sway levels in PD patients for certain stance conditions.
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