What happens to your brain on the way to Mars?

Long-term galactic cosmic ray exposure leads to dementia-like cognitive impairments
May 4, 2015

This is your brain on cosmic rays: Digitally reconstructed images of dendrites (green) and spines (red) of neurons before (left) and after (right) irradiation. The gray (Gy) is a unit of ionizing radiation dose. (credit: Vipan K. Parihar et al./Science Advances)

Exposure to highly energetic charged particles — much like those found in the galactic cosmic rays that bombard astronauts during extended spaceflights — causes significant damage to the central nervous system, resulting in cognitive impairments, according to a UC Irvine radiation oncology open-access study appearing in the May 1 edition of Science Advances.

“This is not positive news for astronauts deployed on a two- to three-year round trip to Mars,” said Charles Limoli, a professor of radiation oncology in UCI’s School of Medicine.

“Performance decrements, memory deficits, and loss of awareness and focus during spaceflight may affect mission-critical activities, and exposure to these particles may have long-term adverse consequences to cognition throughout life.”

The particles (mainly protons and helium nuclei) that compose these galactic cosmic rays are mainly remnants of past supernova events. For the study, researchers subjected mice to charged particle irradiation (fully ionized oxygen and titanium) at the NASA Space Radiation Laboratory at the Brookhaven National Laboratory before being sent back to Limoli’s Irvine lab.

Effects of cosmic rays

The researchers found that exposure to these particles resulted in brain inflammation, which disrupted the transmission of signals among neurons. Imaging revealed how the brain’s communication network was impaired through reductions in the structure of nerve cells called dendrites and spines.

Additional synaptic alterations in combination with the structural changes interfered with the capability of nerve cells to efficiently transmit electrochemical signals. The neural changes were reflected in performance on behavioral tasks designed to test learning and memory.

Similar types of more severe cognitive dysfunction are common in brain cancer patients who have received various radiation treatments at much higher doses. In other research, Limoli studies the impact of chemotherapy and cranial irradiation on cognition.

Cognitive deficits in astronauts would take months to manifest, Limoli said, but the time required for a mission to Mars is sufficient for such deficits to develop. People working for extended periods on the International Space Station do not face the same level of bombardment with galactic cosmic rays, as they are still within the protective magnetosphere of the Earth.

Risks on Mars missions

Limoli’s work is part of NASA’s Human Research Program. Investigating how space radiation affects astronauts and learning ways to mitigate those effects are critical to further human exploration of space, and NASA needs to consider these risks as it plans for missions to Mars and beyond.

But what can be done to protect NASA astronauts on a trip to/from Mars (and other participants on the planned Mars One mission)?

As a partial solution, Limoli said, spacecraft could be designed to include areas of increased shielding, such as those used for rest and sleep. However, many of these highly energetic particles will traverse the ship nonetheless, he noted, “and there is really no escaping them.”

Preventative treatments offer some hope. “We are working on pharmacologic strategies involving compounds that scavenge free radicals and protect neurotransmission,” Limoli said. “But these remain to be optimized and are under development.”

University of Nevada contributed to the study, which NASA supported.

UC Irvine | Mars Brain Animation

Abstract of What happens to your brain on the way to Mars

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. Animal models have revealed an unexpected sensitivity of mature neurons in the brain to charged particles found in space. 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 6 weeks after acute exposure. Animals manifesting cognitive decrements exhibited marked and persistent radiation-induced reductions in dendritic complexity and spine density along medial prefrontal cortical neurons known to mediate neurotransmission specifically interrogated by our behavioral tasks. Significant increases in postsynaptic density protein 95 (PSD-95) revealed major radiation-induced alterations in synaptic integrity. Impaired behavioral performance of individual animals correlated significantly with reduced spine density and trended with increased synaptic puncta, thereby providing quantitative measures of risk for developing cognitive decrements. Our data indicate an unexpected and unique susceptibility of the central nervous system to space radiation exposure, and argue that the underlying radiation sensitivity of delicate neuronal structure may well predispose astronauts to unintended mission-critical performance decrements and/or longer-term neurocognitive sequelae.