April 24, 2014
Animal Study Highlights Potential Cognitive Risks Of Deep Space Travel
redOrbit Staff & Wire Reports - Your Universe Online
Rats exposed to the same types of high-energy particles that astronauts would face during a lengthy deep space mission demonstrated lapses in attentiveness and reduced reaction times, according to research appearing in the April edition of the journal Radiation Research.The cognitive impairment was present even when radiation exposure was in extremely low-dose ranges, the authors noted, and affected a sizable subset of the rodents (but not all of them). The phenomenon appears to be associated with protein changes in the brain, and if the findings turn out to be applicable to humans, it could be possible to develop a biological marker to predict radiation sensitivity prior to deployment on such voyages.
According to lead investigator Dr. Robert D. Hienz, an associate professor of behavioral biology at the Johns Hopkins University School of Medicine, astronauts that travel outside of the Earth’s magnetic field receive only a limited about of protection from radiation exposure from their spaceships. Participating in spacewalks or traveling outside of their vehicles means they will be exposed to the full effects of radiation from solar flares and intergalactic cosmic rays.
Furthermore, since there is no planet-wide magnetic field on either the moon or Mars, those space travelers will likely be exposed to relatively high radiation levels, even once they reach the surface. However, the National Space Biomedical Research Institute-funded study demonstrates that different people will be affected in different ways.
“In our radiated rats, we found that 40 to 45 percent had these attention-related deficits, while the rest were seemingly unaffected,” Hienz explained in a recent statement. “If the same proves true in humans and we can identify those more susceptible to radiation's effects before they are harmfully exposed, we may be able to mitigate the damage.”
If the researchers are able to identify a biomarker for humans, it could also have implications for people other than astronauts as well. For instance, it could cause medical experts to consider other factors when determining the best treatment plan for patients undergoing radiotherapy for brain tumors, as well as helping to identify those men and women facing an increased risk from radiation-based treatment programs.
The new study utilized tests similar in nature to the self-diagnostic fitness for duty exams used by International Space Station astronauts before they participate in mission-critical events such as spacewalks. As part of one such test, an astronaut sees a blank screen on a handheld device, and is told to tap the screen once an LED counter becomes illuminated. Normally, the reaction time is under 300 milliseconds.
The rats used in the experiment had been instructed to touch a light-up key with their noses in a similar experiment, with the study authors recording how quickly they were able to react. They were then exposed to high-energy proton and heavy ion radiation particles similar to those typically occurring in space, only produced by a collider at the Brookhaven National Laboratory in Upton, New York.
Some of the rodents’ heads were exposed to a varying amount of radiation similar to what astronauts would experience during long-duration missions, while others were given mock exposures. They were then tested daily for 250 days. Nineteen of the 46 radiation-sensitive animals showed evidence of impairment, starting as early as 50 days post-exposure and lasting through the end of the study.
“Lapses in attention occurred in 64 percent of the sensitive animals, elevations in impulsive responding occurred in 45 percent and slower reaction times occurred in 27 percent,” the researchers said. “The impairments were not dependent on radiation dose. Additionally, some of the rats didn't recover at all from their deficits over time, while others showed some recovery over time.”
The radiation-sensitive rats which received the highest doses were found to have a higher concentration of transporters for dopamine, a neurotransmitter involved in alertness and attention, the researchers said. They believe that the rodents who were exposed to radiation experienced impairment to their dopamine transport system because the neurotransmitter was most likely not removed as it would have been in a normally-functioning brain.
First author Catherine M. Davis, Ph.D., a postdoctoral fellow in the Department of Psychiatry and Behavioral Sciences, said the results should not necessarily preclude astronauts who are by nature sensitive to radiation to be kept from participating to future missions to Mars or the moon.
However, Davis did emphasize that it would be important for those space travelers to take special precautions, such as wearing extra shielding to protect their brains or not taking part in spacewalks. “As with other areas of personalized medicine,” she explained, “we would seek to create individual treatment and prevention plans for astronauts we believe would be more susceptible to cognitive deficits from radiation exposure.”