The Effects of Galactic Cosmic Rays on the Central Nervous System: From Negative to Unexpectedly Positive Effects That Astronauts May Encounter

SIMPLE SUMMARY: The central nervous system is extremely sensitive to cosmic rays – an ionizing radiation that astronauts encounter during interplanetary missions, particularly to Mars. There are still disputes about how dangerous cosmic rays are to brain health. Our review aimed to analyze the studies on the influence of cosmic rays at flight-related doses on physical development, well-being, emotional state, depressive-like behavior, cognition, neurogenesis and the course of neurodegenerative process. The combined effects of cosmic rays and hypogravity were also the focus of our review. Thus, for the first time a comprehensive picture of radiation-induced changes in the central nervous system is presented: from functional to neurochemical and molecular. Relying on the literature data we conclude that cosmic rays are relatively safe for the central nervous system functions. Moreover, under some irradiation scenarios, it has been shown that cosmic rays enhance cognitive abilities of rodents and nonhuman primates. This effect is often accompanied by hyperactivity, increased orientational-exploratory behavior and, simultaneously, state anxiety. Interestingly, the results of several studies strongly suggest that cosmic rays reverse negative effects of antiorthostatic suspension (a ground-based model of hypogravity). Taken together, these data allow us to be optimistic about the prospects for humanity’s cosmic expansion. ABSTRACT: Galactic cosmic rays (GCR) pose a serious threat to astronauts’ health during deep space missions. The possible functional alterations of the central nervous system (CNS) under GCR exposure can be critical for mission success. Despite the obvious negative effects of ionizing radiation, a number of neutral or even positive effects of GCR irradiation on CNS functions were revealed in ground-based experiments with rodents and primates. This review is focused on the GCR exposure effects on emotional state and cognition, emphasizing positive effects and their potential mechanisms. We integrate these data with GCR effects on adult neurogenesis and pathological protein aggregation, forming a complete picture. We conclude that GCR exposure causes multidirectional effects on cognition, which may be associated with emotional state alterations. However, the irradiation in space-related doses either has no effect or has performance enhancing effects in solving high-level cognition tasks and tasks with a high level of motivation. We suppose the model of neurotransmission changes after irradiation, although the molecular mechanisms of this phenomenon are not fully understood.