New concerns for neurocognitive function during deep space exposures to chronic, low dose rate, neutron radiation

Abstract

As NASA prepares for a mission to Mars, concerns regarding the health risks associated with deep space radiation exposure have emerged. Until now, the impacts of such exposures have only been studied in animals after acute exposures, using dose rates approximately 1.5×10⁵ higher than those actually encountered in space. Using a new, low dose rate neutron irradiation facility, we have uncovered that realistic, low dose rate exposures produce serious neurocognitive complications associated with impaired neurotransmission. Chronic (6 month) low dose (18 cGy) and dose rate (1 mGy/day) exposures of mice to a mixed field of neutrons and photons result in diminished hippocampal neuronal excitability and disrupted hippocampal and cortical long-term potentiation. Furthermore, mice displayed severe impairments in learning and memory, and the emergence of distress behaviors. Behavioral analyses showed an alarming increase in risk associated with these realistic simulations, revealing for the first time, some unexpected potential problems associated with deep space travel on all levels of neurological function.

Significance Statement Simulating the space radiation environment to date has been limited by available technology and restricted by the practicalities of implementing protracted terrestrial-based exposures. Now through the use of a new neutron irradiation facility, capable of simulating the realistic low dose rates found in deep space, we have uncovered striking neurobehavioral and electrophysiological defects in rodents subjected to continuous (6 month) low dose rate (1 mGy/day) neutron exposures. This study represents the first to document the significant adverse consequences of space relevant radiation dose rates on the brain, and points to the heightened risks associated with NASA’s upcoming plans for travel to Mars.