VESTIBULOOCULOMOTOR TESTING DURING THE COURSE OF A SPACEFLIGHT MISSION

The experimental concept and findings from a recent manned orbital spa ceflight are presented. In a single-case, longitudinal study, vestibul o-oculomotor function was examined by caloric testing and active head oscillations. The results from preflight, inflight, and postflight mea surements of the human vestibulo-ocular reflex, together with those of ongoing terrestrial studies, should enable separation of the canalicu lar and otolithic contributions to ocular torsion. This analysis enabl es an accurate evaluation of the adaptation of the otolithic system to the inflight microgravity and, after landing, to the 1-g force enviro nment. Video-oculography was employed throughout for the comprehensive measurement of eye and head movements. Caloric testing involved air i nsufflation at 15-degrees-C over 90 s, followed by an observation inte rval of 2 min. During inflight testing this was continued with a 30-s free-floating interval. Active head oscillations were performed at fou r discrete frequencies (0.12, 0.32, 0.80, 2.0 Hz) and over a frequency sweep between 0.1 and 2.0 Hz. These head oscillations were performed in yaw, pitch, and roll and for three visual conditions (head-fixed ta rget, space-fixed target, no target). The concomitant stimulation of t he semicircular canals and otolithic receptors during these oscillatio ns should yield different oculomotor responses under 1-g and 0-g adapt ations. Both the short-form caloric test and the active head movement test were performed on 4 of the 5 available mission days. The results of the caloric tests yield a caloric nystagmus intensity (slow-phase v elocity) of approximately 60% of that measured before flight and indic ate an adaptation in response over the 10-day period after landing. Th e preliminary results from the head movement tests about the roll axis indicate an adaptive response in this aspect of the vestibulo-ocular reflex during prolonged microgravity. Some changes in sensomotoric con trol were also apparent during the inflight and postflight phases.