Space is a challenging environment for the human body, with a range of factors that can cause damage to our physiology, from head to toe. The head, in particular, is a primary concern. A new study, funded by NASA, has provided a deeper understanding of the issue. Researchers have found that astronauts who have traveled on the International Space Station (ISS) or NASA space shuttles on missions lasting at least six months experienced significant expansion of the cerebral ventricles. This finding suggests that an interval of at least three years would be advisable between longer space missions.
The Study’s Findings
Based on brain scans of 30 astronauts, the researchers found that it took three years for the ventricles to fully recover after such journeys. The cerebral ventricles are the spaces in the middle of the brain that contain cerebrospinal fluid. This colorless and watery fluid flows in and around the brain and spinal cord, cushions the brain to help protect against sudden impact, and removes waste products.
The researchers suggest that if the ventricles do not have sufficient time to recover between back-to-back missions, this may impact the brain’s ability to cope with fluid shifts in microgravity. For example, if the ventricles are already enlarged from a previous mission, they may be less compliant and have less space to expand and accommodate fluid shifts during the next mission. Age-related ventricular enlargement, caused by brain atrophy, can be associated with cognitive decline.
Brain Modifications in Microgravity
The absence of Earth’s gravity modifies the brain and seems to be a mechanical effect. On Earth, our vascular systems have valves that prevent all of our fluids from pooling at our feet due to gravity. In microgravity, the opposite occurs, and fluids shift toward the head. This headward fluid shift likely results in ventricular expansion, and the brain sits higher within the skull.
Study Participants and Implications
The study involved 23 male and seven female astronauts from the US, Canadian, and European space agencies. Eight traveled on space shuttle missions of about two weeks, and eighteen were on ISS missions of about six months, and four were on ISS missions of about a year. Little to no ventricular volume change occurred in astronauts after short missions. Enlargement occurred in astronauts after missions of six months or longer, though there was no difference in those who flew for six months compared to those who did so for a year.
The fact that enlargement did not worsen after six months could be good news for future Mars missions on which astronauts may spend two years in microgravity during the journey. However, this preliminary finding is promising for astronaut brain health during long-duration missions, but it’s still important that we examine MRI data from a larger group of astronauts and following even longer missions.
The absence of enlargement following short flights was good news for people who may consider short space tourism jaunts, as that industry develops. Microgravity conditions also cause other physiological effects due to the reduced physical load on the human body. These include bone and muscle atrophy, cardiovascular changes, issues with the balance system in the inner ear, and a syndrome involving the eyes. Elevated cancer risk from the greater exposure to solar radiation that astronauts may encounter the further they travel from Earth is another concern.
The study’s findings suggest that space travel can have significant impacts on the human brain, and that it may take years for the brain to fully recover from these effects. This has important implications for future space missions, particularly those that involve long periods in microgravity. However, the fact that enlargement did not worsen after six months is promising for future missions, and for the development of the space tourism industry. Ultimately, more research is needed to fully understand the effects of space travel on the human body and brain, and to develop effective strategies for mitigating these effects.
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