Psychoneurological changes during chronic exposure to deep-space radiation

Dr Joaquim Ignácio S da Mota Neto  /  Dr Thais Russomano 

Psychiatrist, Federal University of Pelotas, Brazil / Founder  & Scientific Director, InnovaSpace

The brain is the prime and most complex organ of the human body and within it takes place the sophisticated phenomena that define us as human beings, enabling recognition of and interaction with our surroundings. Basic and primitive survival functions pass through the different formations and axes of the Central and Peripheral Nervous System, but far beyond this are the many other functions that differ in complexity and high degree of neural connectivity, such as those performed by the limbic system, containing the hypothalamus, hippocampus and amygdala. 
These important structures are responsible for integrating and giving context to aspects of emotions, memories and learning, thus building our cognitive capacities. Therefore, it is essential to maintain the functionality of these cerebral regions that permit the acquisition, storage and recall of information, as together with the cerebral cortex, they are fundamental for several aspects of personal, social and professional performance.
The perception of potential fragility of these intricate brain structures is inevitable, when faced with extreme and unknown situations, such as one might encounter on a manned trip to Mars. The effects of different space features, such as radiation or microgravity, may pose a threat not only to the ability of an astronaut to perform both simple and complex tasks, but also to control emotions or react in an adequate manner to a new environment in which access to old memories may become essential. 

A recently published article by Mike Wall of Space.com presented the issue of space radiation and how it can affect the brain function and psychological behaviour of animals, in research using a new scientific approach. The study conducted by Munjal Acharya & Janet Baulch of the University of California and Peter Klein of Stanford University, exposed mice for the first time to a continuous and chronic low-dosage radiation (1mGy/day). The idea of the research team was to mimic a manned trip to Mars, during which astronauts would be exposed to 6 months of low-dosage, deep-space radiation. This type of protocol differs from those previously used, in which animals were submitted to high-dosage radiation over short time periods.

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The space environment is very unique and is full of radiation in the form of galactic cosmic rays, particles of high energy and charge, and solar particle events, which differ from the low-LET (X- or g-rays) radiation that is predominant on Earth. Radiation is known to affect humans in several ways, in three distinct phases: acute, latent and chronic effects. Chemical mediators are first released from damaged cells, particularly from bone marrow, lymphoid tissues and the gastrointestinal tract, leading to symptoms, such as nausea, vomiting and malaise. The latent phase is free of symptoms as it represents the time between the initial cell injury and manifestation of cell renewal. Chronic effects include a decrease in cell count, and increase in the risk of developing cancer, and degenerative and infectious diseases. 
The negative impact of radiation on the Central Nervous System (CNS) has been considered relatively minor, as the CNS is formed of few actively dividing cells, which provides it with a type of natural resistance. Nonetheless, some studies have demonstrated that space radiation could potentially produce undesirable effects on the brain, including a decrease in function and neurodegeneration.
The results from the mice study would seem to corroborate the hypothesis that radiation can indeed cause deleterious effects on the CNS, perhaps due to the longer 6-month period of exposure to the low-dose radiation. These findings, published in the Society for Neuroscience's open-access journal, eNeuro, suggest that mice exposed to radiation had alterations in their hippocampus, the part of the brain responsible for learning and memory, and the prefrontal lobe of the cortex, dedicated to cognitive functions and social relationships. The neurological pathway has yet to be defined, but it is already of serious concern to the space scientific community, as such alterations could cause impairment in psychological performance, especially during stressful and critical situations, like those that could easily be experienced during an interplanetary trip, which is exactly the occasion when clear and immediate decision-making or problem-solving responses are needed!

Under normal conditions on Earth, the human cognitive and emotional processes can struggle to perform well enough to cope with the demands of everyday life, and therefore, the subjective and objective adversities of adapting to a long-duration trip to another planet could be a huge challenge. Even if we are able to control each one of the many physical or psychological variables that could impact on our relationship with the space environment, aerospace science still needs to deal with poorly understood aspects related to the interaction of executive memory with emotions, with experts having highlighted that what we remember is never the same as what was originally set to be fixed in our memory - the material undergoes change in the storage process as each individual adds personal characteristics to the stored element.  
The peculiarities of the human brain and its crossovers between the acts of feeling, thinking, planning and performing have already led humanity to evolve, overcoming innumerous obstacles from the Stone Age to the Modern Era. However, even in a place with no palpable barriers, like the vastness of space, there will be invisible elements, such as radiation, that could be powerful enough to delay or impede human omnipotence and omnipresence in the exploration of the Universe.