Journal of Vestibular Research - Volume 14, issue 6

Authors: Liu, Ping | Gliddon, Catherine M. | Lindsay, Libby | Darlington, Cynthia L. | Smith, Paul F.

Article Type: Research Article

Abstract: Previous studies have shown that peripheral vestibular damage causes long-term neurochemical changes in the hippocampus which may be related to spatial memory deficits. Since recent studies have also demonstrated deficits in non-spatial object recognition memory following vestibular lesions, the aim of the present study was to extend these investigations into the perirhinal cortex (PRC), which is known to be important for object recognition, and the related entorhinal cortex (EC). We examined the effects of unilateral vestibular deafferentation (UVD) on the expression of four enzymes associated with neuronal plasticity, neuronal nitric oxide synthase (nNOS), endothelial nitric oxide synthase (eNOS), arginase I …and arginase II (AI and II), in the rat EC and PRC using Western blotting. Tissue was collected at 10 hs, 50 hs and 2 weeks post-UVD. In the EC and PRC, nNOS protein expression decreased on the contralateral side at 2 weeks post-UVD but not before. At the same time, eNOS protein expression increased in both regions on the contralateral side. In the EC, AII protein expression increased on the ipsilateral side at 2 weeks post-UVD. In the PRC, AI increased and decreased on the contralateral and ipsilateral sides (respectively) at 2 weeks post-UVD. AII showed a bilateral increase in the PRC at 2 weeks post-UVD. These results demonstrate changes in NOS and arginase protein expression in the PRC and EC following UVD, which are unlikely to be due to the initial severity of the vestibular syndrome because they develop well after vestibular compensation has taken place. Neurochemical changes in these regions of the medial temporal lobe may be implicated in the development of object recognition deficits that contribute to cognitive dysfunction following peripheral vestibular damage. Show more

Keywords: nitric oxide, nitric oxide synthase, arginase, vestibular compensation, perirhinal cortex, entorhinal cortex, unilateral vestibular deafferentation

DOI: 10.3233/VES-2004-14601

Citation: Journal of Vestibular Research, vol. 14, no. 6, pp. 411-417, 2004

Authors: Tangorra, James L. | Jones, Lynette A. | Hunter, Ian W.

Article Type: Research Article

Abstract: A method was developed to identify the linear, system level dynamics of the horizontal, angular vestibulo-ocular reflex (VOR) as it stabilized vision during head-free tracking of a visual target. Small amplitude, broad spectrum, stochastic torque perturbations were applied to the head while the subject tracked an unpredictable, moving target with active head and eye motions. Stochastic system identification techniques were used to design the torque and target inputs and to conduct the analysis such that the linear dynamics of the VOR, independently of the visual system's influence on eye motions, were determined. The linear analysis was limited to evaluating VOR …dynamics from approximately 0.5 to 4.5 Hz. Nonlinearities in the head-neck system affected the low frequency response of the head to the torque perturbations, and the eye velocity sequence was affected by nonlinearities and degraded by noise at high frequencies. The VOR's gain was near 1.0 between about 0.5 and 2.5 Hz, and then decreased steadily to 0.85 as the frequency increased towards 4.0 Hz. The VOR phase angle was also frequency dependent and corresponded to VOR eye motions lagging the head's disturbance motion by less than 10 ms at frequencies greater than 1.0 Hz. Show more

Keywords: gaze, head-free tracking, helmet, system identification, vestibulo-ocular reflex, VOR

DOI: 10.3233/VES-2004-14602

Citation: Journal of Vestibular Research, vol. 14, no. 6, pp. 419-441, 2004

Authors: Holly, Jan E.

Article Type: Research Article

Abstract: The vestibular coriolis (or "cross-coupling") effect is traditionally explained by cross-coupled angular vectors, which, however, do not explain the differences in perceptual disturbance under different acceleration conditions. For example, during head roll tilt in a rotating chair, the magnitude of perceptual disturbance is affected by a number of factors, including acceleration or deceleration of the chair rotation or a zero-g environment. Therefore, it has been suggested that linear-angular interactions play a role. The present research investigated whether these perceptual differences and others involving linear coriolis accelerations could be explained under one common framework: the laws of motion in three …dimensions, which include all linear-angular interactions among all six components of motion (three angular and three linear). The results show that the three-dimensional laws of motion predict the differences in perceptual disturbance. No special properties of the vestibular system or nervous system are required. In addition, simulations were performed with angular, linear, and tilt time constants inserted into the model, giving the same predictions. Three-dimensional graphics were used to highlight the manner in which linear-angular interaction causes perceptual disturbance, and a crucial component is the Stretch Factor, which measures the "unexpected" linear component. Show more

Keywords: perception, motion sickness, zero-g, cross-coupling, self-motion

DOI: 10.3233/VES-2004-14603

Citation: Journal of Vestibular Research, vol. 14, no. 6, pp. 443-460, 2004

Authors: Seemungal, B.M. | Gunaratne, I.A. | Fleming, I.O. | Gresty, M.A. | Bronstein, A.M.

Article Type: Research Article

Abstract: A technique for simultaneous measurement of conscious (perceptual) and reflex (nystagmus) thresholds of vestibular function is described. We used an automated modified binary search algorithm with simultaneous infrared oculography in determining perceptual and VOR nystagmic thresholds respectively, during discrete whole body rotations in the dark. In a young group of 14 normal subjects (mean age 23 years) angular acceleration thresholds were significantly higher for perceptual detection (1.18 deg/s/s) than for nystagmus generation (0.51 deg/s/s). Only nystagmic thresholds were slightly raised (0.87 deg/s/s) in an older group of 9 normal subjects (mean age 63 years). The finding that nystagmic thresholds are …lower than perceptual ones indicates a higher sensitivity of brainstem than cortical vestibular mechanisms. This technique would be of particular value in clinical situations where a dissociation between reflex and conscious vestibular mechanisms is expected, e.g. in patients with cortical lesions or in elderly patients with falls. Show more

Keywords: vestibular, sensory thresholds, nystagmus, elderly

DOI: 10.3233/VES-2004-14604

Citation: Journal of Vestibular Research, vol. 14, no. 6, pp. 461-466, 2004

Authors: McGibbon, Chris A. | Krebs, David E. | Wolf, Steven L. | Wayne, Peter M. | Scarborough, Donna Moxley | Parker, Stephen W.

Article Type: Research Article

Abstract: Tai Chi (TC) is a comparatively new intervention for peripheral vestibular hypofunction, which is often treated with vestibular rehabilitation (VR). We compared gaze stability (GZS), whole-body stability (WBS) and footfall stability (FFS) during locomotion among 26 people with vestibulopathy (VSP), randomized into two treatment arms (13 TC and 13 VR). Each intervention program was offered for 10 weeks. GZS improved more for VR than for TC, but WBS (and FFS) improved more for TC than for VR. There was a significant relationship between changes in GZS and WBS for the VR subjects (r = 0.60, p = 0.01), but not …for TC subjects. There was a significant relationship between changes in WBS and FFS for both VR (r = 0.65, p < 0.01) and TC (r = 0.58, p = 0.02) groups; the relationship disappeared in the VR but not the TC group when controlling for GZS. These findings suggest that VR and TC both benefit patients with VSP but via differing mechanisms. Moreover, these data are the first to test the assumption that improving gaze control among patients with VSP perforce improves postural stability: it does not. We conclude that GZS is most improved in those who receive VR, but that TC improves WBS and FFS without improving GZS, suggesting patients with VSP can rely on non-gaze related mechanisms to improve postural control. Show more

Keywords: vestibulopathy, gaze stability, whole body stability, Tai Chi, vestibular rehabilitation

DOI: 10.3233/VES-2004-14605

Citation: Journal of Vestibular Research, vol. 14, no. 6, pp. 467-478, 2004