Space radiation causes mice to become confused and lack curiosity, scientists have discovered. Researchers exposed them to the same types of charged particles found in galactic cosmic rays to see what effect it would have on them.
Published in the journal Science Advances, findings showed that after six weeks, there were distinct changes in the brains of the mice that had been exposed, compared with those that had not.
Charles Limoli, from the University of California, Irvine, showed how the mice had decreased numbers of dendritic synapses – the branched structures protruding from neurons that carry electrochemical signals.
"As Nasa prepares for the first manned spaceflight to Mars, questions have surfaced concerning the potential for increased risks associated with exposure to the spectrum of highly energetic nuclei that comprise galactic cosmic rays," the authors wrote.
"Astronaut autonomy during long-term space travel is particularly critical as is the need to properly manage planned and unanticipated events, activities that could be compromised by accumulating particle traversals through the brain. Using mice subjected to space-relevant fluences of charged particles, we show significant cortical- and hippocampal-based performance decrements six weeks after acute exposure."
Researchers found an unexpected susceptibility of the central nervous system to the space radiation, which they believe may suggest there is an underlying radiation sensitivity that could lead to declines in "mission-critical performance" of astronauts. The charged particles hit the dendritic branches and caused them to break off.
To study the effects, scientists put the mice through a series of experiments to test their learning and memory. They were placed in a box of toys, then changed either the location of the toys or the toys themselves.
The mice that had been exposed to radiation were less curious – in that they were less active – in new situations and became confused more easily.
Limoli told IBTimes UK that if the mice results hold true in human models, the results are worrying: "The radiation-induced changes in neurons of the medial pre-frontal cortex disrupt neurotransmission between the cortex and hippocampus. These brain region are critical for learning and memory and the recognition of novelty.
"The inability to discriminate novelty leads to lack of curiosity and indicates impaired cognition. This may well be problematic in space – as astronauts are required to act autonomously to a variety of unanticipated situations.
"The concerning implications for deep space travel are related to radiation-induced changes [reductions] in the structural complexity of neurons. We have quite a bit more to understand about the space radiation [and non-radiation] environment and the challenges it imposes on human health during space travel.
He said that while specially designed clothing and spacecraft could help limit the exposure, there are limitations because of the payload that can be sent into space. Limoli said: "Normal clothing would not help but specialised helmets or regions within the spacecraft could be designed to be more protective. Pharmacologic strategies are also being developed to counteract the deleterious effects of space radiation on the brain."
The researchers now plan to use improved simulations of radiation fields in space to work out how much longer the adverse affects of radiation last in the brain and to try to develop countermeasures against the problem.
For now, though, Limoli said this looks like another obstacle to overcome before sending humans to Mars. He said: "This is not a deal breaker but rather another complication that should be understood and planned for."