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Principal Investigator:
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Millard F. Reschke, Ph.D.
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Organization:
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NASA-Johnson Space Center
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Project Ended:
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2005
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Clear vision and the ability to locate objects in the environment are prerequisites for reliable performance of motor tasks. In space, astronauts are confronted with a stimulus rearrangement that requires adaptation to function effectively with the new requirements of altered spatial orientation and motor coordination. Both in-flight and post-flight, astronauts have reported disturbances of gaze control. Dr. Millard F. Reschke is exploring the mechanisms related to gaze holding. One measure that is easily quantified is the control of angle of gaze (or line of sight). Reschke is examining methods used to compensate for gaze control problems by observing normal, non-astronaut study participants placed in conditions that alter the gravitational environment and affect the sensory receptors found in muscles, tendons, joints, and the inner ear, that detect the motion or position of the body or a limb. Further tests will be made by studying abnormalities of gaze control in patients with cerebellar disease.
|
Principal Investigator:
|
Millard F. Reschke, Ph.D.
|
|
Organization:
|
NASA-Johnson Space Center
|
|
Project Ended:
|
2005
|
Clear vision is a prerequisite for reliable performance of motor tasks. Space flight confronts the crewmember with a stimulus rearrangement that requires adaptation to function effectively with the new requirements of altered spatial orientation and motor coordination. Adaptation and motor learning, driven by the effects of cerebellar disorders, may share some of the same demands that face our astronauts.
One measure of spatial localization shared by the astronauts and those suffering from cerebellar disorders that is easily quantified and for which a neurobiological substrate has been identified is the control of the angle of gaze (the line of sight). The disturbances of gaze control that have been documented to occur in astronauts, both inflight and postflight, can be directly related to changes in the extrinsic gravitational environment and intrinsic proprioceptive mechanisms, thus lending themselves to description by mathematical models. The basic models can be formulated using normal, non-astronaut test subjects and subsequently extended using centrifugation techniques to alter the gravitational and proprioceptive environment of these subjects. Further tests and extensions of the models can be made by studying abnormalities of gaze control in patients with cerebellar disease. Finally, tests of astronaut subjects during and after exposure to space flight, in association with the corresponding sensory-motor adaptations, will allow us to evaluate and extend our developed understanding of adaptation in the control of eccentric gaze-holding.
The specific aims of this study are:
- To investigate the mechanisms of gaze-holding in normal, non-astronaut subjects with the head held in various orientations with respect to gravity and the head held in various orientations relative to both gravity and the trunk. This will involve characterizing the time constant of centripetal gaze drift - the rate in which the eyes naturally drift back toward the null position following an eccentric eye movement.
- To investigate the mechanisms that adaptively compensate for gaze-holding failure, especially the rebound nystagmus phenomenon, which decreases the rate of centripetal drift of the eyes. We will study the time course of rebound nystagmus in normal, non-astronaut subjects.
- To investigate the stimulus rearrangement and adaptation resulting from exposure to gravitoinertial environments greater than Earths gravity using prolonged exposure to centrifugation.
- To study mechanisms that adaptively compensate for gaze-holding failure in patients with vestibular cerebellar disease who show impaired gaze-holding ability. We will compare gaze-holding defects and rebound nystagmus in patients with that obtained in our normal subjects.
- To compare the gaze-holding abilities of astronaut subjects prior to, during and immediately following space flight with specific predictions made as a consequence of the ground-based research. Tests similar to those performed upon normal, non-astronaut subjects will be conducted to quantify changes in the time constant of centripetal drift of the eyes in relation to changes in the gaze-holding induced as a result of the stimulus rearrangement of space flight.
- To measure the stability of gaze, during all phases of flight, with the eye at the central position in astronauts to investigate the occurrence of saccadic intrusions known as square wave jerks (SWJ), and to relate SWJ mechanisms common to the failure of gaze-holding.
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