The effect of sleep on the adaptation to the cross-coupled stimulus during artificial gravity

Abstract

Head turns performed out of the plane of rotation of an artificial gravity (AG) centrifuge during short radius centrifugation (SRC) result in a cross coupled stimulus (CCS) to the vestibular system. This stimulus, when experienced repetitively by an untrained subject, often leads to motion sickness, inappropriate compensatory eye movements, and a perceived illusory tumbling sensation. Previous studies have shown that subjects can be adapted to the CCS. We investigated the effect of sleep on the rate of adaptation to the CCS over multiple exposure sessions. Subjects performed a sequence of right-quadrant yaw head turns while lying supine on a centrifuge rotating at 23rpm in the clockwise direction. The protocol consisted of 42 spinning head turns per session and a total of three sessions for each subject, over a two-day period. Sessions were performed either in the early morning or late evening with an approximately equal separation time of 10-12 hours between consecutive sessions. Subjects were divided into two experimental groups: group A attended morning-evening-morning sessions and group B attended evening-morning-evening sessions. A total of 33 subjects participated in the experiment, 22 of which provided complete and consistent data sets for the entire three-session protocol. Subjective reports of the tumbling intensity, tumbling duration, and motion sickness were recorded. Eye movement data was also recorded.

(cont.) Adaptation is quantified as a maintained decrease in one or more of the recorded subjective measures or a reduction of the vestibular ocular reflex (VOR) slow phase time constant. The main results were: 1. Sleep increases the rate of adaptation to the CCS. 2. Time of day does not affect the tumbling sensation. 3. Time of day affects motion sickness susceptibility, with morning sessions resulting in higher motion sickness scores than evening sessions.