Development of a countermeasure to enhance sensorimotor adaptation to altered gravity levels

Astronauts experience several gravitational transitions during their journey into space, and they must adapt their sensorimotor capabilities to perform their tasks safely and successfully. A decrement in orientation perception ability or motor skills during a critical mission phase such as landing or docking may lead to catastrophic consequences. The overall objective of this research effort is to investigate and quantify sensorimotor adaptation to altered gravity levels using a short-radius centrifuge. Individual differences, the effect of pre-training in a different gravity environment, and the effect of promethazine in reducing sensorimotor impairment and space motion sickness are of particular interest. The hypotheses are: (1) individual differences exist in the ability to adapt to altered gravity environments and these differences can be predicted for hypo-gravity by measuring adaptability in a hyper-gravity environment, (2) training in one altered gravity environment will improve sensorimotor adaptation in another altered gravity environment, and (3) promethazine will reduce motion sickness, but will have no influence on either basic vestibular perceptual function or sensorimotor adaptation. We are using two tasks to characterize performance decrements and subsequent adaptation that reduces errors: orientation perception and manual control. A series of experiments utilizing these tasks are being conducted on our short-radius centrifuge. For the perception task, subjects report their orientation during a series of roll tilts, while for manual control task, subjects attempt to null a pseudo-random roll tilt disturbance to keep themselves upright using a joystick. We describe preliminary results showing an initial disruption in ability to do both tasks in an altered gravity environment, followed by a learning process to reduce errors. We also tested whether promethazine impacts basic vestibular function by conducting a double-blind, within-subject study with 10 subjects, in which we compared vestibular perceptual thresholds measured with the administration of promethazine or a placebo. Results indicate that promethazine has little effect on perceptual thresholds. Since perceptual measurements can have some inherent measurement variability, we combined subject testing with Monte Carlo simulation tools we developed to evaluate how precisely adaptation rate can be measured. This approach allowed us to optimize experimental design to ensure that precise measures of adaptation rate will be determined. Experimental results show that subjects can, on average, report tilt with a precision of 2°. Simulations show that this corresponds to a coefficient of variation on adaptation time constant of around 20%.