Neurovestibular and Sensorimotor Studies in Space and Earth Benefits (original) (raw)
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Physiological Targets of Artificial Gravity: The Sensory-Motor System
The Space Technology Library
The human sensory-motor system allows us to ascertain the status of our body, sense our environment, make relevant adjustments in relation to this environment, or move around in our environment to achieve various goals. The sensory part, relying on our body's numerous physiological sensors, detects the motion or position of body parts relative to each other (spatial awareness) or to the environment (spatial orientation). The motor part refers to our movement within and relative to our environment. Sensing and moving around in the environment cannot be regarded as separate entities: any movement will stimulate the sensors, and immediately alter their afferent information to the central nervous system (CNS). For example, a rapid head movement is sensed by the vestibular organs, which in turn signal to the extraocular muscles to generate a compensatory eye movement. If this were not the case, blurred vision would occur. In addition to eye-head coordination, the vestibular system is involved in various other human sensory-motor functions, including maintenance of posture, gait stabilization, general coordination of limb movement, and spatial orientation.
Challenges to the Vestibular System in Space: How the Brain Responds and Adapts to Microgravity
Frontiers in Neural Circuits, 2021
In the next century, flying civilians to space or humans to Mars will no longer be a subject of science fiction. The altered gravitational environment experienced during space flight, as well as that experienced following landing, results in impaired perceptual and motor performance—particularly in the first days of the new environmental challenge. Notably, the absence of gravity unloads the vestibular otolith organs such that they are no longer stimulated as they would be on earth. Understanding how the brain responds initially and then adapts to altered sensory input has important implications for understanding the inherent abilities as well as limitations of human performance. Space-based experiments have shown that altered gravity causes structural and functional changes at multiple stages of vestibular processing, spanning from the hair cells of its sensory organs to the Purkinje cells of the vestibular cerebellum. Furthermore, ground-based experiments have established the adap...
Decreased otolith-mediated vestibular response in 25 astronauts induced by long duration spaceflight
Journal of Neurophysiology, 2016
The information coming from the vestibular otolith organs is important for the brain when reflexively making appropriate visual and spinal corrections to maintain balance. Symptoms related to failed balance control and navigation are commonly observed in astronauts returning from space. To investigate the effect of microgravity exposure on the otoliths, we studied the otolith-mediated responses elicited by centrifugation in a group of 25 astronauts before and after 6 mo of spaceflight. Ocular counterrolling (OCR) is an otolith-driven reflex that is sensitive to head tilt with regard to gravity and tilts of the gravito-inertial acceleration vector during centrifugation. When comparing pre- and postflight OCR, we found a statistically significant decrease of the OCR response upon return. Nine days after return, the OCR was back at preflight level, indicating a full recovery. Our large study sample allows for more general physiological conclusions about the effect of prolonged microgra...
The effect of gravity on the horizontal and vertical vestibulo-ocular reflex in the rat
Experimental Brain Research, 2000
Horizontal and vertical eye movements were recorded in alert pigmented rats using chronically implanted scleral search coils or temporary glue-on coils to test the dependence of the vestibulo-ocular reflex (VOR) upon rotation axis and body orientation. The contributions of semicircular-canal versus otolith-organ signals to the VOR were investigated by providing canal-only (vertical axis) and canal plus otolith (horizontal axis) stimulation conditions. Rotations that stimulated canals only (upright yaw and nose-up roll) produced an accurate VOR during middle-and high-frequency rotations (0.2-2 Hz). However, at frequencies below 0.2 Hz, the canal-only rotations elicited a phase-advanced VOR. The addition of a changing gravity stimulus, and thus dynamic otolith stimulation, to the canal signal (nose-up yaw, on-side yaw, and upright roll) produced a VOR response with accurate phase down to the lowest frequency tested (0.02 Hz). In order to further test the dependence of the VOR on gravitational signals, we tested vertical VOR with the head in an inverted posture (inverted roll). The VOR in this condition was advanced in phase across all frequencies tested. At low frequencies, the VOR during inverted roll was anticompensatory, characterized by slow-phase eye movement in the same direction as head movement. The substantial differences between canalonly VOR and canal plus otolith VOR suggest an important role of otolith organs in rat VOR. Anticompensatory VOR during inverted roll suggests that part of the otolith contribution arises from static tilt signals that are inverted when the head is inverted.
Spatial orientation and balance control changes induced by altered gravitoinertial force vectors
Experimental Brain Research, 2001
To better understand the mechanisms of human adaptation to rotating environments, we exposed 19 healthy subjects and 8 vestibular-deficient subjects ("abnormal"; four bilateral and four unilateral lesions) to an interaural centripetal acceleration of 1g (resultant 45°roll-tilt of 1.4g) on a 0.8-m-radius centrifuge for periods of 90 min. The subjects sat upright (body z-axis parallel to centrifuge rotation axis) in the dark with head stationary, except during 4 min of every 10 min, when they performed head saccades toward visual targets switched on at 3-to 5-s intervals at random locations (within ±30°) in the earth-horizontal plane. Eight of the normal subjects also performed the head saccade protocol in a stationary chair adjusted to a static roll-tilt angle of 45°for 90 min (reproducing the change in orientation but not the magnitude of the gravitoinertial force on the centrifuge). Eye movements, including voluntary saccades directed along perceived earth-and head-referenced planes, were recorded before, during, and immediately after centrifugation. Postural center of pressure (COP) and multisegment body kinematics were also gathered before and within 10 min after centrifugation. Normal subjects overestimated rolltilt during centrifugation and revealed errors in perception of head-vertical provided by directed saccades. Errors in this perceptual response tended to increase with time and became significant after approximately 30 min. Motion-sickness symptoms caused approximately 25% of normal subjects to limit their head movements during
Neural readaptation to Earth's gravity following return from space
Journal of neurophysiology, 2001
The consequence of exposure to microgravity on the otolith organs was studied by recording the responses of vestibular nerve afferents supplying the utricular otolith organ to inertial accelerations in four toadfish, Opsanus tau, sequentially for 5 days following two National Aeronautics and Space Administration shuttle orbital flights. Within the first day postflight, the magnitude of response to an applied translation was on average three times greater than for controls. The reduced gravitational acceleration in orbit apparently resulted in an upregulation of the sensitivity of utricular afferents. By 30 h postflight, responses were statistically similar to control. The time course of return to normal afferent sensitivity parallels the reported decrease in vestibular disorientation in astronauts following return from space.
The effect of spaceflight on the otolith-mediated ocular counter-roll
4th Symposium on Space Educational Activities
The otoliths of the vestibular system are seen as the primary gravitational sensors and are responsible for a compensatory eye torsion called the ocular counter-roll (OCR). The OCR ensures gaze stabilization and is sensitive to a lateral head roll with respect to gravity and the Gravito-Inertial Acceleration (GIA) vector during e.g., centrifugation. This otolith-mediated reflex will make sure you will still be able to maintain gaze stabilization and postural stability when making sharp turns during locomotion. To measure the effect of prolonged spaceflight on the otoliths, we measured the OCR induced by off-axis centrifugation in a group of 27 cosmonauts before and after their 6-month space mission to the International Space Station (ISS). We observed a significant decrease in OCR early post-flight, with first- time flyers being more strongly affected compared to frequent or experienced flyers. Our results strongly suggest that experienced space crew have acquired the ability to ada...
Journal of Neurophysiology, 2023
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Visual-vestibular integration as a function of adaptation to space flight and return to Earth
Research on perception and control of self-orientation and self-motion addresses interactions between action and perception [1]. Self-orientation and self-motion, and the perception of that orientation and motion are required for and modified by goal-directed action. Detailed Supplementary Objective (DSO) 604 Operational Investigation-3 (OI-3) was designed to investigate the integrated coordination of head and eye movements within a structured environment where perception could modify responses and where response could be compensatory for perception. A full understanding of this coordination required definition of spatial orientation models for the microgravity environment encountered during spaceflight. The central nervous system (CNS) must develop, maintain, and modify as needed, neural models that may represent three-dimensional Cartesian coordinates for both the self (intrinsic) and the environment (extrinsic). Extrinsic coordinate neural models derive from the observer's ability to detect up/down vector signals produced by gravity (g) and visual scene and polarity (VS). Horizontal coordinates are incompletely specified by the up/down vector. Additional complexity is introduced because extrinsic coordinate models derive from multimodal processes. For example, detection of gravity is mediated by graviceptors at several locations in the body, including the vestibular apparatus (Gves), somatic receptors (Gs), and visceral receptors (Gvic) [2, 3]. Intrinsic coordinate models must be more complex because they may be eye centric, head centric, torso centric, and so on [4]. Intrinsic coordinate models also should differ from those for extrinsic coordinates in that X-, Y-, and Z-axis vectors are all nonarbitrary and physiologically specified [5].