DYNAMICS OF TORSIONAL OPTOKINETIC NYSTAGMUS UNDER ALTERED GRAVITOINERTIAL FORCES

The purpose of the present study was to investigate the influence of v arying gravitoinertial forces on torsional optokinetic nystagmus durin g parabolic flights. Using the scleral search-coil technique, we measu red the gain and phase lag of torsional optokinetic nystagmus (OKN) in duced by a hemispherical visual display rotating about the roll axis e ither at constant velocity or sinusoidally at various frequencies duri ng level flight, hypogravity, and hypergravity. Compared with level fl ight, there was a significant increase in slow-phase eye velocity duri ng hypogravity and an increase in nystagmic frequency. An absence of w ell-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 OKN. The absence of well-developed torsional optokinetic aft ernystagmus suggests that the velocity storage pathways do not contrib ute significantly to the torsional OKN system in humans.