Charles Limoli from University of California, Irvine in the US and colleagues found that exposure to highly energetic charged particles - much like those found in the galactic cosmic rays that will bombard astronauts during extended spaceflights - causes significant long-term brain damage in test rodents, resulting in cognitive impairments and dementia.
The study follows an earlier research that showed somewhat shorter-term brain effects of galactic cosmic rays. The current findings, Limoli said, raise much greater alarm.
"The space environment poses unique hazards to astronauts. Exposure to these particles can lead to a range of potential central nervous system complications that can occur during and persist long after actual space travel - such as various performance decrements, memory deficits, anxiety, depression and impaired decision-making," he said.
"Many of these adverse consequences to cognition may continue and progress throughout life," Limoli said.
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For the study, rodents were subjected to charged particle irradiation (fully ionised oxygen and titanium) at the NASA Space Radiation Laboratory at New York's Brookhaven National Laboratory and then sent to Limoli's UCI lab.
Imaging showed that the brain's neural network was impaired through the reduction of dendrites and spines on these neurons, which disrupts the transmission of signals among brain cells.
These deficiencies were parallel to poor performance on behavioural tasks designed to test learning and memory, researchers said.
The team discovered that the radiation affected "fear extinction," an active process in which the brain suppresses prior unpleasant and stressful associations, as when someone who nearly drowned learns to enjoy water again.
"Deficits in fear extinction could make you prone to anxiety which could become problematic over the course of a three-year trip to and from Mars," Limoli said.
The study appears in the journal Scientific Reports.