title: Directional asymmetry of nystagmus elicitation in humans during step and sinusoidal modes of lateral linear acceleration.
abstract: We investigated nystagmus elicitation in 50 normal subjects who were exposed interaurally to linear acceleration with step (rectangular) and sinusoidal modes of oscillation using a linear accelerator. Relatively strong G-loads of 0.3-0.5 G at a 10 m stroke were applied to subjects who looked at a memorized target in darkness, with the head and trunk tightly restrained in the upright sitting position. Horizontal and vertical eye movements were recorded by electrooculography (EOG). Various levels of G-directional preponderance (DP), including completely one-sided, were observed similarly in either stimulus mode, strongly suggesting that directional asymmetry in nystagmus elicitation may be a functional characteristic in the otolith-ocular response, in contrast to the canal-ocular response. The effects of G-load increase were less congruent between the two stimulus modes. In the step-mode oscillation, the desaccaded slow eye position which corresponds to the vestibuloocular reflex (VOR) was saw-toothed in shape as was the stimulus velocity curve, but the baseline often drifted slowly and DP-dependently in the direction opposite to the fast phase of nystagmus. When the slow phase velocity (SPV), a slope of the saw-tooth, was adjusted mathematically for such slow drift, it revealed that the adjusted SPVs were almost symmetrical between rightward and leftward G-directions. These results suggest that DP generation is separate from VOR generation which is primarily symmetrical.
authors.affiliation: Space Medicine Research Center, Research Institute of Environmental Medicine, Nagoya University, Furo-cho, Chikusa-ku, 464-8601, Nagoya, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Katayama
authors.forename: S
authors.initials: S
authors.lastname: Mori
mesh_terms: D000054:Acceleration / Q000009:adverse effects*; D000293:Adolescent; D000328:Adult; D002490:Central Nervous System / Q000502:physiology; D004585:Electrooculography; D005260:Female; D006112:Gravitation; D018466:Gravity Sensing / Q000502:physiology*; D006801:Humans; D008297:Male; D009760:Nystagmus, Physiologic / Q000502:physiology*; D009801:Oculomotor Muscles / Q000294:innervation / Q000502:physiology; D009949:Orientation / Q000502:physiology; D004856:Postural Balance / Q000502:physiology*; D011930:Reaction Time; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*; D015203:Reproducibility of Results; D014722:Vestibule, Labyrinth / Q000502:physiology*