Journal of Vestibular Research - Volume 3, issue 2

Authors: Demer, Joseph L. | Oas, John G. | Baloh, Robert W.

Article Type: Research Article

Abstract: We studied visual-vestibular interaction (VVI) in 9 normal human subjects using active and passive vertical head rotations. Gain and phase of the vertical vestibulo-ocular reflex (VOR) and visually enhanced vestibulo-ocular reflex (VVOR) were measured for single frequency sinusoidal motion, as well as for sinusoidal motion of continuously increasing frequency, over the range of 0.4 to 4.0 Hz. In addition to measurement of VVOR during normal vision, telescopic spectacles having a magnification of 1.9× were used to challenge VVI to facilitate measurement of visual enhancement of VOR gain. In the mid-frequency range (1.6 to 2.4 Hz), the active VOR exhibited gain …closer to compensatory than did the passive VOR; at other frequencies, active and passive VOR gains were similar. VVOR gain during normal vision was compensatory for both active and passive motion throughout the frequency range tested. VVOR gain with 1.9× telescopic spectacles was greater than VOR gain at all frequencies tested, including up to 3.2 Hz for passive bead movements, and up to 4.0 Hz for active head movement. However, gain enhancement with telescopic spectacles was consistently greater during active than during passive head movement. Phase errors for the VOR and VVOR were small under all testing conditions. Although active VOR and VVOR were directionally symmetrical, gain of upward slow phases differed from that of downward slow phases for passive VOR and VVOR in a manner depending on rotational frequency. For both active and passive testing, gain and phase values obtained during swept frequency rotations were similar to those obtained during single frequency sinusoidal testing. These data indicate that VVI can enhance gain of the passive vertical VOR even at frequencies above what is usually considered to be the upper limit of visual pursuit tracking. The additional enhancement observed during active bead movements at these high frequences is attributable to use of efference copy of the skeletal motor command to neck musculature. Show more

Keywords: active bead movement, passive head movement, vertical, visual-vestibular interaction

DOI: 10.3233/VES-1993-3201

Citation: Journal of Vestibular Research, vol. 3, no. 2, pp. 101-114, 1993

Authors: Leigh, R. John | Seidman, Scott H. | Grant, Michael P. | Hanna, Joseph P.

Article Type: Research Article

Abstract: We report a patient with a long-standing, unilateral lesion of the midbrain who showed ipsidirectional loss of torsional quick phases, impairment of all vertical eye movements and normal horizontal eye movements. The findings are consistent with recent reports of the effects of experimental lesions, in monkeys, of the,rostral interstitial nucleus of the medial longitudinal fasciculus and the interstitial nucleus of Cajal.

Keywords: midbrain, torsional eye movements, nystagmus, vestibulo-ocular reflex

DOI: 10.3233/VES-1993-3202

Citation: Journal of Vestibular Research, vol. 3, no. 2, pp. 115-121, 1993

Authors: Merfeld, Daniel M. | Young, Laurence R. | Paige, Gary D. | Tomko, David L.

Article Type: Research Article

Abstract: Three-dimensional squirrel monkey eye movements were recorded during and immediately following rotation around an earth-vertical yaw axis (160∘ /s steady state, 100∘ /s2 acceleration and deceleration). To study interactions between the horizontal angular vestibulo-ocular reflex (VOR) and head orientation, postrotatory VOR alignment was changed relative to gravity by tilting the head out of the horizontal plane (pitch or roll tilt between 15∘ and 90∘ ) immediately after cessation of motion. Results showed that in addition to post rotatory horizontal nystagmus, vertical nystagmus followed tilts to the left or right (roll), and torsional nystagmus followed forward or backward (pitch) …tilts. When the time course and spatial orientation of eye velocity were considered in three dimensions, the axis of eye rotation always shifted toward alignment with gravity, and the postrotatory horizontal VOR decay was accelerated by the tilts. These phenomena may reflect a neural process that resolves the sensory conflict induced by this postrotatory tilt paradigm. Show more

Keywords: vestibulo-ocular reflex, eye movements, otolith organs, semicircular canals, monkey

DOI: 10.3233/VES-1993-3203

Citation: Journal of Vestibular Research, vol. 3, no. 2, pp. 123-139, 1993

Authors: Merfeld, Daniel M. | Young, Laurence R. | Oman, Charles M. | Shelhamert, Mark J.

Article Type: Research Article

Abstract: A “sensory conflict” model of spatial orientation was developed. This mathematical model was based on concepts derived from observer theory, optimal observer theory, and the mathematical properties of coordinate rotations. The primary hypothesis is that the central nervous system of the squirrel monkey incorporates information about body dynamics and sensory dynamics to develop an internal model. The output of this central model (expected sensory afference) is compared to the actual sensory afference, with the difference defined as “sensory conflict”. The sensory conflict information is, in turn, used to drive central estimates of angular velocity (“velocity storage”), gravity (“gravity storage”), and …linear acceleration (“acceleration storage”) toward more accurate values. The model successfully predicts “velocity storage” during rotation about an earth-vertical axis. The model also successfully predicts that the time constant of the horizontal vestibulo-ocular reflex is reduced and that the axis of eye rotation shifts toward alignment with gravity following postrotatory tilt. Finally, the model predicts the bias modulation, and decay components that have been observed during off-vertical axis rotations (OVAR). Show more

Keywords: spatial orientation, model, vestibulo-ocular reflex, monkey

DOI: 10.3233/VES-1993-3204

Citation: Journal of Vestibular Research, vol. 3, no. 2, pp. 141-161, 1993

Authors: Tolu, E. | Pugliatti, M.

Article Type: Research Article

Abstract: The aim of this study was to investigate whether, and in what way, the vestibular input may influence the activity of the masseter muscles. The variations in the spontaneous electrical activity and the evoked responses in the masseter motor units to natural or electrical activation of the vestibular afferents were recorded in anesthetized guinea pigs. The effects of a unilateral lesion of the labyrinth on the firing rate of the masseter motor units were also studied. Results show that: 1) vestibular input elicited an excitatory tonic control on masseter muscle activity; 2) a faster labyrinthine control is driven to the …contralateral than the homolateral masseter muscles; 3) vestibular macular input does exert an asymmetrical control on masseteric muscles of both sides, in relation to the head displacement in space. The latencies of responses recorded from the masseter motor units suggest that polysynaptic pathways are involved in connecting the vestibular system to the trigeminal complex. The possible anatomical substrates for this vestibulomasseteric reflex are discussed. Show more

Keywords: vestibular system, masseter muscles, vestibulomasseteric reflex

DOI: 10.3233/VES-1993-3205

Citation: Journal of Vestibular Research, vol. 3, no. 2, pp. 163-171, 1993

Authors: Padoan, Serge | Fransson, Per Anders | Magnusson, Mans | Johansson, Rolf

Article Type: Research Article

Abstract: The effects of subanesthetic (21%) nitrous oxide (N2 O) narcosis on postural control, as measured by posturography were studied in 12 subjects. Vibration induced body sway, with open and closed eyes, and body sway induced by a visual stimulus were evaluated. Adaptation was measured as the quotient of body sway variance between the second and first halves of each trial. Change in postural strategy was evaluated as change in the variance of shear forces relative to change in body sway. Subjective evaluation of narcosis was recorded. Body sway variance increased significantly during exposure to N2 O, and equally for all …body sway inducing stimuli. With tbe eyes open, adaptation to vibratory perturbation was significantly reduced by N2 O. Postural strategy was unaffected by N2 O, but differed significantly between stimuli, with relatively less involvement of shear forces during vibratory perturbation in the eyes open condition than during the other body sway inducing stimuli. Subjective evaluation of narcosis correlated with body sway variance during the visual stimulus. The present findings indicate that subanesthetic N2 O narcosis reduces postural control. Adaptation to a balance disturbing stimulus, with undisturbed vision, is decreased by N2 O. Visual clues are shown to be crucial to the postural strategy adopted to maintain balance. The effects of N2 O are assumed to be due to impairment of sensorimotor integration in the CNS. Show more

Keywords: posture, adaptation, vision, vibration, N20

DOI: 10.3233/VES-1993-3206

Citation: Journal of Vestibular Research, vol. 3, no. 2, pp. 173-180, 1993

Authors: Tiliket, Caroline | Shelhamer, Mark | Tan, H. Stevie | Zee, David S.

Article Type: Research Article

Abstract: We investigated the influence of static head orientation and position, relative to the axis of body rotation, upon vestibular adaptation. With the head centered, displaced anterior to the axis of body rotation, or tilted 40∘ to 45∘ in roll or pitch, the gain of the vestibulo-ocular reflex (VOR) was trained (to go either up or down) for one hour using artificial manipulation of the visual surround to produce a visual-vestibular mismatch. Before and after each training session, the VOR was measured in darkness with the head in the training as well as in several non-training positions. We found …that transfer of VOR adaptation to non-training positions was almost complete when comparing head eccentric versus head-centered rotations. For tilts, however, transfer of VOR learning was far less complete suggesting that static otolith signals provide a strong contextual cue that gates the expression of an adaptive VOR response. Finally, following training to increase than VOR, gain was greater for centripetally than centrifugally directed slow phases. Centripetally directed postsaccadic drift also developed. These fundings imply that the gain increase paradigm also leads to abnormal function of the velocity-to-position neural integrator, which holds eccentric positions of gaze. Show more

Keywords: VOR, adaptation, context specificity, transfer

DOI: 10.3233/VES-1993-3207

Citation: Journal of Vestibular Research, vol. 3, no. 2, pp. 181-195, 1993