Study of spatial orientation and posture regulation under IG and microgravity

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Same Coriolis stimulation was applied to five young adult males, at 1 G and μ G during parabolic flights and with occluded vision, postural changes and ocular movements were recorded. Postural changes were recorded using a linear accelerometer, and the distance of movement was derived. Ocular movement was recorded to video, and via image analysis, horizontal, vertical, and torsional components were derived. The following conclusions were obtained.1)With the head tilted during rotation, the upper body was linearly accelerated to the direction of inertial input at 1 G. Under μ G, the body was first accelerated to the direction of inertial force, and, second, to the direction of inertial input. The displacement in a one-second period after head tilt during rotation at 100 degrees/second was 10 cm in the direction of inertial input at 1 G, and 4 cm in the direction of inertial force under μG.2)Irrespective of 1 G or μG, ocular movement was consistent with inertial input. Nystagmus peak slo … More w-phase velocity immediately after head tilt, either of horizontal, vertical or torsional component, did not indicate clear differences between both conditions.3)At 1 G, external coordinates in which gravity functions as the Z axis are used as the reference for the inertial input, but at μ G as this reference disappears, inertial force does not produce output. Therefore, at μ G, sensation of motion is weak and postural responses to the inertial input disappear.4)Even if external references disappear under μ G, as inertial input for the head as a reference still applies, a similar degree of nystagmus is induced to that seen with 1 G.It is surmised that the inertial input from vestibular organs produces spatial movement information by referring external coordinates reproduced in the vestibular nuclei. This coordinate information produces a sensation of motion within the cerebral cortex, and by coordinate conversion through the vestibulocerebellar tract, posture is uniformly changed by the cerebellum. Less