This article reviews current challenges to health in space and has a secondary intention to set the tone for this special supplement on 'Extra-Terrestrial Neurosciences'. The effects of microgravity, radiation, isolation, disturbance in circadian rhythms and the hostile environment on the cardiovascular, neurological, immunological and various biological human systems are discussed here. Alterations in physiology, environmental hazards, and mitigative safety measures are briefly discussed along with challenges encountered in providing remote diagnoses and health care during space missions.

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This article presents a review of the current findings related to neurovestibular physiology, aetiology, and proposed theories on space motion sickness (SMS) during acute and sustained exposure to microgravity. The review discusses the available treatment options including medication and nonpharmacological countermeasure methods that help to prevent the development of SMS in weightlessness. Ground-based simulations using virtual reality, flight simulations, and Barany's chairs can be applied to study SMS and demonstrate its signs and symptoms to space crew members. Space motion sickness has been observed in approximately 70% of astronauts within the first 72 h in microgravity, having in general an instantaneous onset of signs and symptoms. Stomach discomfort, nausea, vomiting, pallor, cold sweating, salivation, tachypnoea, belching, fatigue, drowsiness, and stress hormone release have been documented. This can have detrimental effects on the well-being of astronauts in the initial phase of a space mission. Mental and physical performance may be affected, jeopardizing operational procedures and mission safety.

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Microgravity (MG) is one of the main problems that astronauts have to cope with during space missions. Long-duration space travel can have detrimental effects on human neurophysiology. Despite scientific efforts, these effects are still insufficiently investigated. Animal earth-based analogs are used to investigate potential nervous system associated perturbations that might occur during prolonged space missions. Hindlimb unloading, Tail suspension and Pelvic suspension models are currently used in MG studies. Loss of homeostasis of certain biological pathways in the nervous system can lead to the functioning and expression of receptors/genes, and the release and functioning of neurotransmitters and neuronal membrane ion channels into specific brain regions. The potential impact of MG on molecular mechanisms linked to neurophysiology through animal earth-based analogs is reviewed. The effect of molecular signalling pathways on the decline of neuronal connectivity and cognitive and neuroplasticity function under MG simulated conditions will be studied. The role of biomarkers including neurotransmitters, genes or receptors will be highlighted in the healthy and MG-affected brain. MG-mediated neurodegenerative mechanisms linked to learning and memory impairment will be highlighted. This review depicts the current rodent models applied to simulate MG ground based approaches and investigates the MG induced changes in the nervous system. The neuropathological profile of the above animal MG ground-based models can be comparable to the effects of ageing, anxiety and other neurological disorders. The advantages and limitations of the existing approaches are discussed. MG induced neurophysiology outcomes can be extrapolated to study other clinical applications.

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Space exploration exposes astronauts to a variety of gravitational stresses. Exposure to a reduced gravity environment affects human anatomy and physiology. Countermeasures to restore homeostatic states within the human body have begun. The pathophysiological effects of exposure to microgravity, on the neurological system, are, however, still not clear. NASA has scheduled deep space exploration of extraterrestrial locations such as the Moon and Mars in the 2030s. Adverse health effects related to the human exposure to microgravity from previous, relatively shorter missions have been documented. A lengthy deep space travel to Mars could be overburdened by significant adverse health effects. Astronauts demonstrate a significant increase in the number of many types of circulating white blood cells (neutrophils, monocytes, T-helper cells, and B-cells) but a decrease in natural killer cells. It is unclear whether these changes are due to increased production or decreased clearance of these cells. In this review, viral reactivation in astronauts will be discussed, including the occurrence of clinical cases before, during, or after spaceflight and their management during and after flight. Studies on models used in spaceflight studies such as the AKATA cells (an immortalized B-cell line derived from a Japanese patient with Burkitt's lymphoma, a tumor induced by Epstein–Barr virus) and other cell lines which shed these latent viruses, will be reviewed with specific reference to gravitational changes, radiation, and spaceflight-induced immune suppression.

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Over the past 60 years, our ability to live and work in space has evolved. From short sojourns in small spacecraft to landing on the moon and residing in an orbiting international space station, we have learned to adapt to an extreme environment and safely return home. Human missions to the Moon, Mars, and exploration of deep space are different. This paper summarizes the challenges of providing medical care, specifically mental health care during long-duration flights. Considerable information about challenges that crews bound for Mars will face is available. Literature regarding this issue is summarized. This manuscript provides a short historical summary of long-duration spaceflight to date; the challenges including limited communication with mission controllers on Earth; and, a summary of the behavioral impacts space flight has had on humans. A look at how the future autonomous systems might support physical and mental health when definitive care is millions of miles away, is also provided. Human spaceflight to Mars or other distant sites will require new approaches to mission preparedness and inflight medical support systems. Exploration class missions will be more autonomous than anything deployed until now. The concepts of telemedicine that have aptly supported crews from the 1960s to the present will no longer be in real-time. While communication between Earth and Mars is possible, it will be characterized by significant time delays. Mars-based crews will need to have systems onboard and on Mars to support all health and performance issues.

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Over the last decade, the National Aeronautics and Space Administration's (NASA) Space Medicine Division has documented a variety of unusual physiological and pathological neuro-ophthalmic findings in astronauts during and following long duration space flight. These ndings include optic disc swelling, globe flattening, choroidal folds, and hyperopic shifts in refraction. Cephalad fluid shift has been proposed as a possible unifying etiology, but the specific mechanism responsible for these changes remains obscure. This manuscript reviews the history, clinical findings, and potential neurophysiological etiologies for spaceflight-associated neuro-ocular syndrome.

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This review addresses central nervous system (CNS) physiological changes during inter-planetary missions, specifically sensorimotor processing and sleep disorders. Isolation, confinement and induced stress factors also have a detrimental effect on cognitive and mental well-being, which could jeopardize mission accomplishment. Although countermeasures have been proposed, they mostly focus on cardiovascular and/or musculoskeletal systems. Long-term space flights require optimal cognitive performance of crew members during weightlessness for longer time periods independent of ground support. The present study describes various countermeasures trends in neuroscientific data acquisition and future perspectives of advanced analysis through functional connectivity and graph theory. These could be used to identify early deterioration patterns and evaluate the robustness of countermeasures employed.

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Context: With a long duration return mission to Mars on the horizon, we must learn as much about the environment and its influence on the musculoskeletal system as possible to develop countermeasures and mitigate deleterious health effects and maladaptation. Aims: To determine the influence of simulated Mars gravity on the activity of four locomotor muscles while walking, in comparison to 1 G, using lower body positive pressure (LBPP). Material and Methods: A total of 14 male subjects (mean age: 20.6 ± 2.4 years) performed bouts of walking in both simulated Mars gravity (0.38 G) and Earth gravity (1 G) using an LBPP device. The dependent variables were the muscle activity evoked in the tibialis anterior, vastus lateralis, gluteus maximus and lateral portion of the gastrocnemius, measured using electromyography and expressed as percentages of maximum voluntary isometric contractions, and heart rate (HR). For statistical analysis, a paired t-test was performed. Statistical significance was defined as P < 0.05. Results: No significant differences in muscle activity were found across conditions for any of the investigated muscles. A significant mean difference in the HR was identified between Earth (105.15 ± 8.1 bpm) and Mars (98.15 ± 10.44 bpm) conditions (P = 0.027), wherein the HR was lower during the Mars trial. Conclusions: The Mars environment may not result in any deteriorative implications for the musculoskeletal system. However, if future research should report that stride frequency and thus activation frequency is decreased in the simulated Mars gravity, negative implications may be posed for muscle retention and reconditioning efforts on the Red Planet.

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