Vestibular adaptation to centrifugation does not transfer across planes of head rotation

Abstract

Out-of-plane head movements performed during fast rotation produce non-compensatory nystagmus, sensations of illusory motion, and often motion sickness. Adaptation to this cross-coupled Coriolis stimulus has previously been demonstrated for head turns made in the yaw (transverse) plane of motion, during supine head-on-axis rotation. An open question, however, is if adaptation to head movements in one plane of motion transfers to head movements performed in a new, unpracticed plane of motion. Evidence of transfer would imply the brain builds up a generalized model of the vestibular sensory-motor system, instead of learning a variety of individual input/output relations separately. To investigate, over two days 9 subjects performed pitch head turns (sagittal plane) while rotating, before and after a series of yaw head turns while rotating. A Control Group of 10 subjects performed only the pitch movements. The vestibulo-ocular reflex (VOR) and sensations of illusory motion were recorded in the dark for all movements. Upon comparing the two groups we failed to find any evidence of transfer from the yaw plane to the pitch plane, suggesting that adaptation to cross-coupled stimuli is specific to the particular plane of head movement. The findings have applications for the use of centrifugation as a possible countermeasure for long duration spaceflight. Adapting astronauts to unconstrained head movements while rotating will likely require exposure to head movements in all planes and directions.