title: Modification of vertical OKN and vertical OKAN asymmetry in humans during parabolic flight.
abstract: Characteristics of human vertical optokinetic nystagmus (OKN) and afternystagmus (OKAN) were examined by ISCAN imaging system on the ground and on board NASA's KC-135 aircraft in a parabolic flight study. The aircraft produced alternating periods of micro-(ca. 10(-2) G) and hyper-(ca. 1.8 G) gravitoinertial forces. Each phase lasted approximately 20 to 25 s. As compared to the baseline data on the ground, there was a significant increase of downward OKN/OKAN, whereas the upward OKN/OKAN did not change significantly in either micro- or hyper-G. As a consequence, the asymmetry of vertical OKN/OKAN, normally seen on the ground, was lost. It is postulated that the increase of downward OKN/OKAN in non-1-G conditions was governed by two different mechanisms. In micro-G, the normal inhibition effect in 1 G on the downward eye movement mediated by otolith organ activity to vertical velocity storage was removed. In hyper-G, downward OKN/OKAN was facilitated by augmented otolith-ocular reflex because of increased gravitoinertial force, so as to produce enhanced compensatory downward eye movement.
authors.affiliation: Department of Physiology, University of Manitoba, Winnipeg, Canada.
authors.forename: G
authors.initials: G
authors.lastname: Wei
authors.forename: S
authors.initials: S
authors.lastname: Lafortune-Kahane
authors.forename: D
authors.initials: D
authors.lastname: Ireland
authors.forename: R
authors.initials: R
authors.lastname: Jell
mesh_terms: D000328:Adult; D004585:Electrooculography; D005133:Eye Movements / Q000502:physiology; D005260:Female; D018470:Gravity, Altered; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D017120:Nystagmus, Optokinetic / Q000502:physiology*; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*; D013026:Space Flight; D014893:Weightlessness