Before we begin to answer this question, it is important to understand the basic overview of white matter and extracellular fluid. Brain white matter is located in the deep tissue of the brain wherein lie nerve fibers (a multitude of nerves) that transmit messages throughout via electrical impulses (MedlinePlus, 2019). Also, white matter is known to develop until about a person’s middle ages (Lee et al., 2019). Extracellular fluid is body fluid, or in this case brain fluid, located outside of cells.
To start, of the 26 astronauts 15 were used to conduct the final analysis (median age 47.2, 12 men, 3 women) from whom data was collected between 2010-2015 (Lee et al., 2019). Researchers preformed diffusion magnetic resonance imaging (dMRI) on astronauts to measure their white matter (Lee et al., 2019). In other words, a brain scan was performed that measured water molecules in the area of white matter. But, why is this of any interest? Well, after returning to earth (where gravity has a greater effect on their body function), astronauts generally feel a lack of orientation, impaired motor control, as well as balancing and cognitive changes (Patel, 2019). Notably, there is a lot of force that is exerted on the brain during space flight which does cause shifts in the upward and downward direction… but despite this, we still don’t really know the effects this might have on white matter. Furthermore, as mentioned previously, white matter generally does not stop developing until around middle years and the median age of the astronauts was 47.2 years – this is worrisome because of possible affects on brain development and fitness for future/longer space missions (Patel, 2019).
To summarize before we get to the findings, there are many physical forces that are exerted on the human brain as it journeys to and from space and certain components that are still undergoing development (i.e. white matter) or necessary for neurological/cognitive function (i.e. fluid balance/extracellular fluid) have to adjust to maintain equilibrium (or homeostasis).
The data suggested that spaceflight did decrease the fluid that surrounds the top of the head while the fluid around the bottom of the hear increased (Patel, 2019), this was not all that surprising since the force exerted on the head while moving in the upwards direction at supersonic speed would push against everything traveling in its direction oppositely. But nevertheless, the result did show that fluid was displaced during that flight phase. However, they were able to determine changes in white matter in the area of the brain responsible for balance, movement, visual and special orientation (Patel, 2019). And those with more white matter had greater trouble with the aforementioned functionalities. Even even more interesting, astronauts who traveled to space more, had fewer intracranial fluid movement (less fluid being displaced in their head) – this was regardless of how much time they spent in space (Patel, 2019). In summary, the more trips they do the less fluid movement they had, and the more likely that the brain is learning to adjust to its environment. Wild!
That being said, there is still a lot we do not know about these changes in assessing whether or not they are good or bad. Researchers are now also trying to uncover what the follow-up MRI imaging may show about the changes in white matter and their implications for when astronauts readjust to earth.
References:
Lee JK, Koppelmans V, Riascos RF, Hasan KM, Pasternak O, Mulavara AP, ... & Seidler RD. (2019). Spaceflight-associated brain white matter microstructural changes and intracranial fluid redistribution. JAMA neurology, 76(4), 412-419.
Patel NV. (2019, March 18). Space changes your brain in bigger ways than we thought. Retrieved from https://www.popsci.com/space-travel-brain-health/.
White matter of the brain: MedlinePlus Medical Encyclopedia. (2019). Retrieved from https://medlineplus.gov/ency/article/002344.htm.
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