Young LR, Teiwes W, Clarke AH, Merfeld DM, Oman CM, Scherer H.

Aviat Space Environ Med. 1993 May; 64: 438.

Man-Vehicle Laboratory, Massachusetts Institute of Technology, Cambridge 02139.

INTRODUCTION. The otolith organs in the inner ear sense the orientation of the head with respect to gravity. Gravity is abruptly lost during space flight. Hypotheses to explain the accompanied Space Adaptation Syndrome early in space are therefore based on a false interpretation of the changed otolith information, which is later compensated by a central adaptation. The function of the otolith organs can be objectively measured by the induced ocular torsion (OT). In order to investigate the contribution of each otolith organ--sacculus and utriculus--to OT and the processing of their information in the central vestibular system, we studied the OT response to linear acceleration. METHODS. Utricular and saccular organs were stimulated using dynamic linear acceleration along the inter-aural y axis (primarily utriculi) and longitudinal z-axis (primarily sacculi) using a linear sled. Sinusoidal stimuli (0.7g) at four frequencies (0.35, 0.5, 0.75 and 1Hz) were employed. Eye movements were recorded in y-axis monocularly using Video-Oculography and in z-axis binocularly using the scleral search coil technique. RESULTS. OT response during z-axis acceleration (0.5 degree) is smaller than during y-axis acceleration (3 degrees). Amplitudes of the response decreases with increasing frequencies and phases are closer to velocity than to acceleration. Binocular recordings during z-axis acceleration show that the remaining OT response is disconjugate while the overall y-axis response is conjugate. CONCLUSION. OT is primarily elicited by y-axis acceleration, hence by stimulation of the utricular organs. Amplitudes and phases of the responses can not fully be explained by peripheral mechanisms, hence a central influences are evident. The disconjugate torsional response during z-axis acceleration may be explained by an anatomic otolith asymmetry or a residual from a central processing. Improved measurement techniques allow us now to access otolith function non-invasively in aerospace environments.

Publication Types:

• Meeting Abstracts

Keywords:

• Acceleration
• Axis
• Eye Movements
• Gravitation
• Head
• Movement
• Orientation
• Otolithic Membrane
• Space Flight
• NASA Discipline Neuroscience
• NASA Discipline Number 16-10
• NASA Program Space Physiology and Countermeasures
• Non-NASA Center

Other ID:

• 95607634

UI: 102212608

From Meeting Abstracts