Journal of Vestibular Research - Volume 6, issue 3

Article Type: Other

DOI: 10.3233/VES-1996-6307

Citation: Journal of Vestibular Research, vol. 6, no. 3, pp. I-III, 1996

Authors: Tomlinson, R.D. | McConville, K.M.V. | Na, E.-Q.

Article Type: Research Article

Abstract: A total of 74 neurons that lacked eye movement sensitivity were recorded within the confines of the rostral medial and medial lateral vestibular nuclei. Of these, 36 had response characteristics that were consistent with combined canal and otolith inputs (CAOT neurons), 18 received canal inputs only (CA neurons), and 20 had otolith inputs only (OT neurons). Responses were measured during both rotational and combined rotational and translational stimuli at 0.5 and 3.0 Hz. The otolith signal was found to lag acceleration markedly at both frequencies. Indeed, one subset of CAOT neurons had otolith responses that led translational velocity by only …12° at 0.5 Hz. All translation-responsive neurons decreased their phase lag with respect to acceleration when the stimulus frequency was increased and exhibited a large increase in sensitivity. As these cells have response dynamics that lie between those seen in otolith afferents and those required to drive the motoneurons during the translational VOR, they may represent an intermediate stage in the signal processing. Show more

Keywords: vestibular translation, primate, VOR

DOI: 10.3233/VES-1996-6301

Citation: Journal of Vestibular Research, vol. 6, no. 3, pp. 145-158, 1996

Authors: Wall III, C. | Arakawa, G.K.

Article Type: Research Article

Abstract: Rotation about the vertical stimulates primarily the horizontal semicircular canals and produces compensatory horizontal nystagmus whose slow component velocity response during constant velocity can be approximated as having a simple exponential decay time constant, TVOR , Constant velocity yaw rotation about a horizontal axis stimulates both the horizontal canals and the otolith organs, producing two additional nystagmus components thought to be of otolithic origin: a steady component called bias and a periodic component known as modulation. We tested a group of 7 human subjects using rotation about each of these axes. We found a strong, negative correlation (r=0.956) between these …individuals' dominant time constants, TVOR , and the magnitude of their modulation components. Canal and otolith signals originate from different parts of the same endorgan and travel separately to the vestibular nucleus. The reflexive eye movements in response to these inputs are thought to be the result of additional processing by the central vestibular and ocular motor systems. Thus, the source of these strongly correlated otolith-ocular and canal-ocular reflex components could logically be due to common factors affecting peripheral transduction or to a subsequent common central processing step. Using anatomical measurements of human vestibular end organs, biophysical endorgan models, and models of central vestibular processes, we examined the alternatives to determine which was the most likely. Correlations were not found between TVOR and the anatomical data or between the TVOR and the biophysical model elements. However, modifications of the velocity storage integrator of Raphan to incorporate either a high pass filter (HPF) or a lowpass filter input for otolith modulation signals allowed for the desired strong negative correlation between TVOR and modulation. We argue in favor of the HPF configuration because it better explains the tendency for the modulation component to increase in amplitude as the modulation frequency is increased. In the above mentioned representation of the central processing of vestibular afferent inputs, we conclude that the modulation component input to the vestibuloocular reflex is within the indirect pathway, but it is “down stream” from the velocity storage integrator. Show more

Keywords: vestibulo-ocular reflex, model, otoliths, central vestibular function, velocity storage integrator

DOI: 10.3233/VES-1996-6302

Citation: Journal of Vestibular Research, vol. 6, no. 3, pp. 159-171, 1996

Authors: Nuti, Daniele | Vannucchi, Paolo | Pagnini, Paolo

Article Type: Research Article

Abstract: Benign paroxysmal positional vertigo of the horizontal semicircular canal (HC-BPPV) is a well-defined syndrome characterized by direction-changing horizontal positional nystagmus. We report the clinical features of 5 patients who illustrate the possible variables of the syndrome. In most cases, nystagmus is geotropic and more intense when the pathological ear is lowermost; less often the syndrome presents with apogeotropic nystagmus that is more intense when the affected ear is uppermost. The nystagmus pattern may vary in time in the same patient, changing from apogeotropic to geotropic even in observations at short intervals. In some patients, the features indicate involvement of more …than one canal, either simultaneously or in succession. It is sustained that the clinical findings can be explained by movement of endolymph caused by displacement of otoconia in the semicircular canals and that variants are due to different positions of the otoconia within the canals. Show more

Keywords: horizontal semicircular canal, benign positional vertigo, paroxysmal nystagmus, canalolithiasis

DOI: 10.3233/VES-1996-6303

Citation: Journal of Vestibular Research, vol. 6, no. 3, pp. 173-184, 1996

Authors: Darlington, Cynthia L. | Smith, Paul F.

Article Type: Research Article

Abstract: This theoretical paper describes the “intrinsic mechanism hypothesis”, a new hypothesis of vestibular compensation, the behavioral recovery that follows unilateral deafferentation of the vestibular labyrinth (UVD). The most salient characteristic of vestibular compensation is the decrease in the severity of the static ocular motor and postural symptoms that follow UVD, associated with a recovery of resting activity in the ipsilateral vestibular nucleus complex (VNC). The speed of static compensation in some mammalian species (for example, cat) has suggested that reactive synaptogenesis is an unlikely explanation because it is too slow. Other, more rapid mechanisms, such as denervation supersensitivity, receptor-up-regulation, or …increased neurotransmitter release, were reasonable possibilities. However, to date, each study that has addressed these possibilities has failed to find any change that could account for the recovery of VNC resting activity. The search for such “substitutive” mechanisms was based on the hypothesis that something other than the VNC neurons themselves would have to “replace” the missing resting activity that the ipsilateral vestibular nerve normally provides. However, brainstem slice studies demonstrate that, at least in vitro, VNC neurons do not need the vestibular nerve in order to generate resting activity. On the basis of these and other considerations, we suggest that following a brief calcium-induced diaschisis, VNC neurons ipsilateral to the UVD reactivate the intrinsic membrane properties that normally contribute to their resting activity in vivo, and that this recovery of resting activity accounts for static vestibular compensation. Show more

Keywords: vestibular compensation, unilateral labyrinthectomy, vestibular nerve transection, vestibular nucleus

DOI: 10.3233/VES-1996-6304

Citation: Journal of Vestibular Research, vol. 6, no. 3, pp. 185-201, 1996

Authors: Bridgeman, D. | Hoffman, L. | Wackym, P.A. | Micevych, P.E. | Popper, P.

Article Type: Research Article

Abstract: The distribution of choline acetyltransferase messenger RNA (mRNA) among efferent vestibular neurons in the chinchilla was investigated. mRNA coding for choline acetyltransferase, the enzyme that synthesizes acetylcholine, was used as a marker for the cholinergic system. In order to retrogradely label the efferent vestibular neurons, Fluoro-gold was injected through the oval window into the inner ear of anesthetized young male chinchillas (6 to 12 months old). The animals were anesthetized and perfused through the heart 2 days post injection with 4% paraformaldehyde in phosphate buffer. Retrogradely labeled efferent vestibular neurons were mapped in brainstem sections prior to processing for in …situ hybridization histochemistry using radiolabeled ribonucleic acid probes complementary to the 3' end of the choline acetyltransferase mRNA. At the levels of the ascending facial nerve and the genu of the facial nerve, we found that approximately 90% of the Fluoro-gold labeled cells in group E1 contained choline acetyltransferase mRNA. All of the group E2 cells that were labeled with Fluoro-gold were found to be cholinergic (contain choline acetyltransferase mRNA). Finally, 60% of the Fluoro-gold-Iabeled cells in the caudal pontine reticular nucleus contained choline acetyltransferase mRNA. Show more

Keywords: chinchilla, choline acetyltransferase, efferent vestibular neurons, Fluoro-gold, gene expression

DOI: 10.3233/VES-1996-6305

Citation: Journal of Vestibular Research, vol. 6, no. 3, pp. 203-212, 1996

Authors: Citek, Karl | Ebenholtz, Sheldon M.

Article Type: Research Article

Abstract: The positions of both eyes were measured objectively in the dark following “look straight ahead” instructions for 16 subjects at 27 combinations of static pitch and roll postures over 360° of space, using an infrared video technique. Shifts in vertical version, or the doll reflex, varied sinusoidally with pitch and roll angle. At 0° roll, the average response has a peak-to-trough amplitude of 9.28° and is symmetric about a downward eye position of 4.63°. The proposed Dual Otolith Model (DOM), based on a combination of utricular and saccular inputs, provided excellent fits to the present data (R2 =0.876) and to …the data of previous studies (R2 =0.916 to 0.994). Deviations in horizontal version varied sinusoidally with roll angle, with no significant effect of pitch angle. In general, clockwise (right-ear-down) rolls produced rightward eye movements, and counterclockwise (Ieft-ear-down) rolls produced leftward eye movements. The average versions were symmetric about a leftward eye position of 1.14°, with a peak-to-trough amplitude of 3.76°. The data were well represented by the proposed Horizontal Version Model (HVM; R2 =0.796), which depended only on utricular input. Show more

Keywords: vertical version, horizontal version, otolith organs, otolith-ocular reflexes

DOI: 10.3233/VES-1996-6306

Citation: Journal of Vestibular Research, vol. 6, no. 3, pp. 213-228, 1996