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Space travel presents a number of environmental challenges to the central nervous system, including changes in gravitational acceleration that alter the terrestrial synergies between perception and action, galactic cosmic radiation that can damage sensitive neurons and structures, and multiple factors (isolation, confinement, altered atmosphere, and mission parameters, including distance from Earth) that can affect cognition and behavior. Travelers to Mars will be exposed to these environmental challenges for up to 3 years, and space-faring nations continue to direct vigorous research investments to help elucidate and mitigate the consequences of these long-duration exposures. This article reviews the findings of more than 50 years of space-related neuroscience research on humans and animals exposed to spaceflight or analogs of spaceflight environments, and projects the implications and the forward work necessary to ensure successful Mars missions. It also reviews fundamental neurophysiology responses that will help us understand and maintain human health and performance on Earth. [ABSTRACT FROM AUTHOR]

Abstract: Preliminary results of an ongoing study examining the effects of space flight on astronauts' motion perception induced by independent tilt and translation motions are presented. This experiment used a sled and a variable radius centrifuge that translated the subjects forward-backward or laterally, and simultaneously tilted them in pitch or roll, respectively. Tests were performed on the ground prior to and immediately after landing. The astronauts were asked to report about their perceived motion in response to different combinations of body tilt and translation in darkness. Their ability to manually control their own orientation was also evaluated using a joystick with which they nulled out the perceived tilt while the sled and centrifuge were in motion. Preliminary results confirm that the magnitude of perceived tilt increased during static tilt in roll after space flight. A deterioration in the crewmember to control tilt using non-visual inertial cues was also observed post-flight. However, the use of a tactile prosthesis indicating the direction of down on the subject's trunk improved manual control performance both before and after space flight. [Copyright &y& Elsevier]

Experiments performed in orbit on the central nervous system have focused on the control of posture, eye movements, spatial orientation, as well as cognitive processes, such as three-dimensional visual perception and mental representation of space. Brain activity has also been recorded during and immediately after space flight for evaluating the changes in brain structure activation during tasks involving perception, attention, memory, decision, and action. Recent ground-based studies brought evidence that the inputs from the neurovestibular system also participate in orthostatic intolerance. It is, therefore, important to revisit the flight data of neuroscience studies in the light of new models of integrative physiology. The outcomes of this exercise will increase our knowledge on the adaptation of body functions to changing gravitational environment, vestibular disorders, aging, and our approach towards more effective countermeasures during human space flight and planetary exploration. [ABSTRACT FROM AUTHOR]

Abstract: Although the mechanisms of neural adaptation to weightlessness and re-adaptation to Earth-gravity have received a lot of attention since the first human space flight, there is as yet little knowledge about how spatial orientation is affected by partial gravity, such as lunar gravity of 0.16g or Martian gravity of 0.38g. Up to now twelve astronauts have spent a cumulated time of approximately 80h on the lunar surface, but no psychophysical experiments were conducted to investigate their perception of verticality. We investigated how the subjective vertical (SV) was affected by reduced gravity levels during the first European Parabolic Flight Campaign of Partial Gravity. In normal and hypergravity, subjects accurately aligned their SV with the gravitational vertical. However, when gravity was below a certain threshold, subjects aligned their SV with their body longitudinal axis. The value of the threshold varied considerably between subjects, ranging from 0.03 to 0.57g. Despite the small number of subjects, there was a significant positive correlation of the threshold with subject age, which calls for further investigation. [Copyright &y& Elsevier]

Abstract: This investigation examined depth and distance perception of 3-D objects presented in stereoscopic vision. The results obtained in normal gravity and microgravity in parabolic flight were compared. This experiment was performed during an ESA campaign of parabolic flight on the Airbus A300 Zero-G on six free-floating subjects. The subjects were first presented with a 3-D cube and were instructed to adjust one dimension (width, length, or height) of the cube so that all three dimensions had the same perceived length. The subjects perceived a normal cube to be taller, thinner, and shallower in microgravity compared to normal gravity. Consequently, when they adjusted its dimension so that it looked “normal” to them, they made it shorter, wider, and deeper. A simple distance perception test confirmed that the subjects underestimated the distance of objects in the depth plane in microgravity. These results confirm a role of the gravitational reference in the 3-D perception of the objects and the environment. [Copyright &y& Elsevier]

Abstract: Many experts believe that artificial gravity will be required for an interplanetary mission. However, despite its attractiveness as an efficient, multi-system countermeasure and its potential for simplifying operational activities, much still needs to be learned regarding the human response to rotating environments before artificial gravity can be successfully implemented. The European Space Agency (ESA) Topical Team on Artificial Gravity recommended a comprehensive program to determine the gravity threshold required to reverse or prevent the detrimental effects of microgravity and to evaluate the effects of centrifugation on various physiological functions. Part of the required research can be accomplished using animal models on a dedicated centrifuge in low Earth orbit. Studies of human responses to centrifugation could be performed during ambulatory, short- and long-duration bed rest, and in-flight studies. Artificial-gravity scenarios should not be a priori discarded in Moon and Mars mission designs. One major step is to determine the relationship between the artificial gravity dose level, duration, and frequency and the physiological responses of the major body functions affected by spaceflight. Once its regime characteristics are defined and a dose–response curve is established, artificial gravity should serve as the standard against which all other countermeasure candidates are evaluated, first on Earth and then in space. [Copyright &y& Elsevier]

Abstract: The occurrence of geometric orientation illusions and the perception of ambiguous figures were analyzed in 24 subjects during static body tilt relative to gravity on Earth. Results showed that illusions such as the Rock''s diamond/square, the Ponzo illusion, and orientation contrast illusions occurred less frequently, and that depth reversal of ambiguous figures took more time when subjects were lying on their side or supine compared to upright, thus suggesting that the gravitational reference plays a significant role in these “visual” illusions. The structure of images, our representation of the environment, and orientation relative to gravity are all integral parts in interpreting visual images. In a weightless environment where no gravitational reference can be used, it is expected that similar alterations in visual perception will occur. [Copyright &y& Elsevier]

Regulatory systems are affected in space by exposure to weightlessness, high-energy radiation or other spaceflight-induced changes. The impact of spaceflight occurs across multiple scales and systems. Exploring such interactions and interdependencies via an integrative approach provides new opportunities for elucidating these complex responses. This paper argues the case for increased emphasis on integration, systematically archiving, and the coordination of past, present and future space and ground-based analogue experiments. We also discuss possible mechanisms for such integration across disciplines and missions. This article then introduces several discipline-specific reviews that show how such integration can be implemented. Areas explored include: adaptation of the central nervous system to space; cerebral autoregulation and weightlessness; modelling of the cardiovascular system in space exploration; human metabolic response to spaceflight; and exercise, artificial gravity, and physiologic countermeasures for spaceflight. In summary, spaceflight physiology research needs a conceptual framework that extends problem solving beyond disciplinary barriers. Administrative commitment and a high degree of cooperation among investigators are needed to further such a process. Well-designed interdisciplinary research can expand opportunities for broad interpretation of results across multiple physiological systems, which may have applications on Earth. [ABSTRACT FROM AUTHOR]

Abstract: One of the most significant problems associated with long duration space missions is mitigating the harmful effects of microgravity on the human body. These effects include loss of bone, muscle mass, and red blood cells; fluid shifts; cardiovascular and sensory-motor deconditioning; and changes in the immune system. If the long-duration exploration missions currently envisioned are to be successfully achieved, countermeasures to address the deleterious effects of microgravity must be developed, tested, and proven. A possible experiment to determine what level of artificial gravity is required for human perception is explored in this paper and involves creating artificial gravity onboard the Space Shuttle. Two methods are examined using Matlab analysis and simulation studies. The first requires putting the Shuttle into an eccentric orbit about its nominal orbit that would generate the centripetal forces necessary to simulate a gravitational environment. The other is a tumble maneuver, similar to the standard maneuver performed prior to Shuttle re-entry. Results indicate that the later maneuver is well within the capability of the Space Shuttle orbital control system, while the former is not. [Copyright &y& Elsevier]

The purpose of this study was to determine whether the absence of gravitational cues during weightlessness could alter the posture and static eye deviation of Earth compensated rats with peripheral vestibular lesions. The responses of bilaterally (BL) and unilaterally (UL) labyrinthectomized rats at a compensated stage (40–43 days after lesion) during parabolic flight were compared with those at an acute stage (2–7 h after lesion) on Earth. When free-floating in 0 g, UL animals showed the same postural pattern as during water immersion just after surgery. The most striking observation was a continuous roll body motion at about 4 Hz, and a skewed asymmetric posture. When restrained in 0 g, static eye deviation was also comparable to that observed at an acute stage. A return to a compensated posture and gaze was observed within a few seconds following the end of the weightlessness conditions. BL animals were less affected. These results suggest that vestibular compensation after unilateral lesion can be disrupted momentarily and is a fragile state during which the otolith system in the remaining vestibular apparatus presumably plays a continuous role. [Copyright &y& Elsevier]