title: Dynamics of torsional optokinetic nystagmus under altered gravitoinertial forces.
abstract: The purpose of the present study was to investigate the influence of varying gravitoinertial forces on torsional optokinetic nystagmus during parabolic flights. Using the scleral search-coil technique, we measured the gain and phase lag of torsional optokinetic nystagmus (OKN) induced by a hemispherical visual display rotating about the roll axis either at constant velocity or sinusoidally at various frequencies during level flight, hypogravity, and hypergravity. Compared with level flight, there was a significant increase in slow-phase eye velocity during hypogravity and an increase in nystagmic frequency. An absence of well-developed torsional optokinetic afternystagmus was observed in all three gravity conditions. Other characteristics included a lack of a slow rise component. These data suggest that otolith inputs do affect torsional optokinetic afternystagmus suggests that the velocity storage pathways do not contribute significantly to the torsional OKN system in humans.
authors.affiliation: Defence and Civil Institute of Environmental Medicine, North York, Ontario, Canada.
authors.forename: B S
authors.initials: BS
authors.lastname: Cheung
authors.forename: K E
authors.initials: KE
authors.lastname: Money
authors.forename: I P
authors.initials: IP
authors.lastname: Howard
mesh_terms: D000054:Acceleration / Q000009:adverse effects*; D000328:Adult; D005133:Eye Movements / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017120:Nystagmus, Optokinetic / Q000502:physiology*; D010037:Otolithic Membrane / Q000502:physiology; D010775:Photic Stimulation; D011187:Posture; D014794:Visual Fields / Q000502:physiology; D014893:Weightlessness / Q000009:adverse effects*