Vestibulo-oculomotor testing during the course of a spaceflight mission.

The experimental concept and findings from a recent manned orbital spaceflight are presented. In a single-case, longitudinal study, vestibulo-oculomotor function was examined by caloric testing and active head oscillations. The results from preflight, inflight, and postflight measurements of the human vestibulo-ocular reflex, together with those of ongoing terrestrial studies, should enable separation of the canalicular and otolithic contributions to ocular torsion. This analysis enables an accurate evaluation of the adaptation of the otolithic system to the inflight microgravity and, after landing, to the 1-g force environment. Video-oculography was employed throughout for the comprehensive measurement of eye and head movements. Caloric testing involved air insufflation at 15 degrees C over 90 s, followed by an observation interval of 2 min. During inflight testing this was continued with a 30-s free-floating interval. Active head oscillations were performed at four 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 target, space-fixed target, no target). The concomitant stimulation of the semicircular canals and otolithic receptors during these oscillations should yield different oculomotor responses under 1-g and 0-g adaptations. 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 velocity) of approximately 60% of that measured before flight and indicate an adaptation in response over the 10-day period after landing.(ABSTRACT TRUNCATED AT 250 WORDS)