Labyrinthine lesions and motion sickness susceptibility |
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Authors: | Mingjia Dai Theodore Raphan Bernard Cohen |
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Institution: | (1) Department of Neurology, Mount Sinai School of Medicine, 1 East 100th Street, Box 1135, New York, NY 10029-6574, USA;(2) Department of Computer and Information Science, Brooklyn College, CUNY, Brooklyn, NY 11210, USA |
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Abstract: | The angular vestibulo-ocular reflex (aVOR) has a fast pathway, which mediates compensatory eye movements, and a slow (velocity
storage) pathway, which determines its low frequency characteristics and orients eye velocity toward gravity. We have proposed
that motion sickness is generated through velocity storage, when its orientation vector, which lies close to the gravitational
vertical, is misaligned with eye velocity during head motion. The duration of the misalignment, determined by the dominant
time constant of velocity storage, causes the buildup of motion sickness. To test this hypothesis, we studied bilateral labyrinthine-defective
subjects with short vestibular time constants but normal aVOR gains for their motion sickness susceptibility. Time constants
and gains were taken from rotational responses. Motion sickness was generated by rolling the head while rotating, and susceptibility
was assessed by the number of head movements made before reaching intolerable levels of nausea. More head movements signified
lower motion sickness susceptibility. Labyrinthine-defective subjects made more head movements on their first exposure to
roll while rotating than normals (39.8 ± 7.2 vs 13.7 ± 5.5; P < 0.0001). Normals were tested eight times, which habituated their time constants and reduced their motion sickness susceptibility.
Combining data from all subjects, there was a strong inverse relationship between time constants and number of head movements
(r = 0.94), but none between motion sickness susceptibility and aVOR gains. This provides further evidence that motion sickness
is generated through velocity storage, not the direct pathway, and suggests that motion sickness susceptibility can be reduced
by reducing the aVOR time constant. |
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Keywords: | Nystagmus Vestibular Velocity storage GABA |
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