Journal of Vestibular Research - Volume 8, issue 4

Authors: Manzoni, D. | Pompeiano, O. | Andre, P.

Article Type: Research Article

Abstract: The vestibulospinal (VS) reflexes elicited by animal rotation modify the activity of limb musculature, thus preserving balance and postural stability. We investigated whether the orientation of these postural responses is strictly dependent upon the direction of head displacement or else can be modified by extralabyrinthine inputs to the goal of stabilizing body position. The experiments were performed in decerebrate cats, in which the effects of static body-to-head displacements were tested on the multiunit EMG responses of the medial head of the triceps brachii to wobble of the whole animal at 0.15 Hz, 10°, both in the clockwise (CW) and counterclockwise …(CCW) direction. These stimuli allowed us to determine the muscle response vector, whose orientation component corresponds to the direction of head displacement giving rise to the maximal EMG response. When the animal body was kept straight with respect to the head, the triceps response vector was always oriented close to the transverse axis, pointing to the side-down direction. Following 30° of body-to-head displacement around a vertical axis passing through the first-second cervical joints, the response vectors of both the left and the right muscles shifted in the same direction of body rotation, thus remaining approximately perpendicular to the body axis. The change in muscle vector orientation corresponded on the average to the angle of body-to-head displacement. Only slight changes in amplitude of the muscle responses were observed. These findings imply that the maximal activation of the triceps brachii always occurred for the same direction of body displacement, irrespective of the pattern of discharge of vestibular afferents, which is determined by the direction of head displacement. The rotation of the triceps response vector induced by body-to-head displacement was reduced or suppressed by inactivation of the ipsilateral cerebellar anterior vermis, following local microinjection of the GABAA agonist muscimol. These findings indicate that 1) the sensory input which results from changing the body position with respect to the head, probably originating from neck receptors, is able to modify the pattern of the VS reflexes, which appear to be organized in a body-centered reference frame, and 2) the cerebellar vermis is required for the proper execution of this sensorimotor transformation. Show more

Keywords: vestibulospinal reflexes, spatial properties, reference frame, proprioceptive neck influences, cerebellar vermis

DOI: 10.3233/VES-1998-8401

Citation: Journal of Vestibular Research, vol. 8, no. 4, pp. 283-297, 1998

Authors: Howard, Ian P. | Zacher, James E. | Allison, Robert S.

Article Type: Research Article

Abstract: We measured post-rotatory nystagmus and sensations of body rotation in standing subjects brought to rest in the dark after 3 minutes of each of the following conditions: 1) passive turning about the mid-body axis, involving only vestibular stimulation, 2) active turning about the mid-body axis, involving both vestibular stimulation and motor-proprioceptive activity in the legs, and 3) stepping round while remaining facing in the same direction on the center of a rotating platform with the head held in a stationary holder (apparent turning), involving only motor-proprioceptive activity. The same acceleration-velocity profile was used in all conditions. Post-rotatory nystagmus (slow phase) …occurred in the same direction to passive body turning and was reduced in velocity after active body turning. After apparent turning, nystagmus was in the opposite direction as attempted body turning. Our theoretical analysis suggests that nystagmus after active turning should conform to the mean of the responses after passive and apparent turning rather than to their sum. The results conform more closely to the mean than to the sum, but with greater weight given to vestibular inputs than to motor-proprioceptive inputs. Post-rotatory sensations of self-rotation were in the expected opposite direction after passive turning and were lower in magnitude after active turning. After apparent turning, sensations of self-rotation were in the same direction as those after attempted turning-an effect known as the antisomatogyral illusion. Show more

Keywords: nystagmus, arthrokinetic nystagmus, turning sensations, antisomatogyral illusion

DOI: 10.3233/VES-1998-8402

Citation: Journal of Vestibular Research, vol. 8, no. 4, pp. 299-312, 1998

Authors: O'Leary, Dennis P. | Davis, Linda L.

Article Type: Research Article

Abstract: Useful medical diagnostic information has been reported from low-frequency rotational testing of the horizontal vestibulo-ocular reflex (VOR) of patients with vestibular disorders. Servocontrolled rotating systems have been used as the only practical method to generate stimuli over lower VOR frequency response ranges, the decade from 0.01 to 0.1 Hz. Active head movements have been used for testing the human VOR at higher frequencies, exceeding 0.5 Hz. We examined whether active head movements could be used also to test the VORs of subjects over lower frequency ranges, extending to 0.02 Hz. We used a swept-frequency, active head movement protocol to generate …a broad-band stimulus. Eye position was recorded with electro-oculography. Head velocity was recorded with a rotational sensor attached to a head band. Six individual test epochs from human subjects were concatenated to form complex, periodic waveforms of head and eye velocity, 75 seconds in duration. Broad-band crossspectral signal processing methods were used to compute horizontal VOR system characteristics from these waveforms extending from 0.02 to 2 Hz. The low-frequency VOR data appeared to originate from amplitude modulation of high-frequency active movements, acting as carrier signals. Control experiments and processing of simulated data from a known system excluded the possibility of signal processing artifacts. Results from six healthy subjects showed low-frequency gains and phase values in ranges similar to those from published rotational chair studies of normal subjects. We conclude that it is feasible to test the human VOR over extended low-frequency ranges using active head movements because of amplitude modulation of the head and eye signals. Show more

Keywords: vestibulo-ocular reflex, active-head, low-frequency, human

DOI: 10.3233/VES-1998-8403

Citation: Journal of Vestibular Research, vol. 8, no. 4, pp. 313-324, 1998

Authors: Zucca, Gianpiero | Valli, Stefano | Valli, Paolo | Perin, Paola | Mira, Eugenio

Article Type: Research Article

Abstract: It is well known that most episodes of benign paroxysmal positional vertigo (BPPV), even in untreated, recover spontaneously in 2 to 6 weeks. In the present study, we put forward the hypothesis that this is mainly due to the fact that endolymph, owing to its low calcium content (20μM) is able to dissolve otoconia. To support this, the fate of frog saccular otoconia immersed in normal endolymph (Ca2+ content 20μM) and in Ca2+ -rich endolymphatic fluids (up to 500μM) was studied by observing the crystals at regular intervals for 3 weeks. The results demonstrated that normal endolymph can dissolve …otoconia very rapidly (in about 20 hours). When the endolymphatic Ca2+ content was increased (50 to 200μM) otoconia dissolution time was slowed down (about 100 to 130 hours, respectively) and completely stopped when the endolymphatic Ca2+ content was of 500μM. The present results therefore suggest that the major process involved in the spontaneous recovery of BPPV episodes is the capability of the endolymph to dissolve dislodged otoconia. Show more

Keywords: BPPV, otoconia, cupulolithiasis, canalolithiasis

DOI: 10.3233/VES-1998-8404

Citation: Journal of Vestibular Research, vol. 8, no. 4, pp. 325-329, 1998

Authors: Viirre, Erik | Draper, Mark | Gailey, Clark | Miller, David | Furness, Thomas

Article Type: Short Communication

Abstract: Six subjects with histories of vertigo and with vestibulo-ocular reflex (VOR) gains less than 0.5 were tested in an adaptation protocol. After initial VOR testing in the dark, the subjects had a computer-driven visual display system placed on their heads. The system had the capability for variation of visual image magnification. The magnification was set to be 5% greater than the subject's average VOR gain. Subjects then performed active head movements as they carried out a visual searching task looking for objects in a panoramic scene. After 6 minutes with each image, the magnification was increased by 3 to 5%. …The process was repeated for a total of 5 images, for a total increase in magnification of approximately 20% over 30 minutes. The VOR gain was measured again. In 17 of 18 conditions tested, the VOR gain increased. The average increase was 16%. Significant increases in VOR gain occurred at 0.32 and 0.64 Hz. The VOR gain increase in these patients occurred in a visual environment that lowered VOR gain in normal subjects. These results suggest that the VOR has an adaptation mechanism tuned to correct for small changes in required gain. Further research is necessary to determine if this method can result in persistent VOR gain improvements and reduction in symptoms and disability in patients with vestibular disorders. Show more

Keywords: vestibulo-ocular reflex, adaptation, gain, increments

DOI: 10.3233/VES-1998-8405

Citation: Journal of Vestibular Research, vol. 8, no. 4, pp. 331-334, 1998

Authors: Calkins, D.S.

Article Type: Research Article

Abstract: When the dependent (or response) variable response variable in an experiment has direction and magnitude, one approach that has been used for statistical analysis involves splitting magnitude and direction and applying univariate statistical techniques to the components. However, such treatment of quantities with direction and magnitude is not justifiable mathematically and can lead to incorrect conclusions about relationships among variables and, as a result, to flawed interpretations. This note discusses a problem with that practice and recommends mathematically correct procedures to be used with dependent variables that have direction and magnitude for 1) computation of mean values, 2) statistical contrasts …of and confidence intervals for means, and 3) correlation methods. Show more

Keywords: statistical analysis, vector data, data with magnitude and direction, means of vector data, statistical analysis of vector data

DOI: 10.3233/VES-1998-8406

Citation: Journal of Vestibular Research, vol. 8, no. 4, pp. 335-340, 1998