Astronauts’ brains can offer valuable insight into the circulation in the brain

The brain is one of the most valuable things we have. But to the around 400,000 Danes who suffer from brain conditions, it is also an organ that makes their everyday lives difficult.

Therefore, this week is International Brain Awareness Week, where patient associations, among others, strive to generate attention to the challenges of having a sick brain.

And sometimes, someone unexpected offers a helping hand. In the US, a Danish researcher and doctor is trying to learn more about the functions of the brain.

Lonnie Grove Petersen from the Department of Biomedical Sciences at the University of Copenhagen is researching a particular group of people who can help us improve our understanding of the brain.

’These subjects are healthier than regular people. At least when we send them on their way. But when they return, something has happened to their brain’, she says.

She is speaking about astronauts. They are healthier than most of us but exposed to an environment that is anything but normal, and this makes them a really good case for understanding the functions of the brain.

Astronaut brains resemble patients with rare condition

Once they have returned to Earth, some astronauts exhibit symptoms and findings that bares some resemblance with that of patients suffering from too much fluid in the brain and elevated fluid pressure in the skull.

Patients on Earth also have other symptoms that set the diseases apart, including debilitating headaches and reduced function of the brain, which can lead to dementia, walking impairments, involuntary urination or defecation

But unlike astronauts, these conditions are often innate and the cause is still unknown, which means that the only available therapy is symptom relief. However, the structural changes are similar, and some functional changes also have similarities with early phases of the terrestrial diseases. 

‘We may be able to learn something from astronauts. They are unlikely to have been born with these conditions, and even though most improve after they have returned to Earth,  it's not the case for all of them. The discovery of the changes in the rain of astronauts is so new that we still do not have long-term follow-ups and we do not fully understand the recovery process. But it looks like in some cases the conditions do become chronic. If we are able to identify the mechanisms triggering the development of these disorders, this knowledge may be transferred to and benefit patients. This way, space medicine does not simply help ensure missions into space, but may also prove useful to us down here on Earth’, says Lonnie Grove Petersen.

Long-term space missions seem to increase the risk of brain disorders

Back when astronauts spent around than a week in space at a time, researchers did not find any signs of danger. This changed, though, as mission length has increased to the now standard 6-month and future missions of 1-year.

'The first symptoms were visual disorders. Their myopic vision deteriorated, and they lost the ability to focus. It is vital both to the individual astronaut, but also to the success of the entire mission that they are able to read instruments and the instructions they receive. Therefore, a lot of research has focussed on studying these visual changes’, she explains.

NASA, ESA and agencies all over the world have thoroughly examined the back of astronauts’ eyes and learned that changes to the eye structure have led to swelling of the optic nerve.

’It turns out that astronauts develop a sort of oedema towards the back of the eye and swelling of the optic nerve. These changes resemble the ones we see in patients with overload of fluid or elevated pressure in the skull. And when the brain was examined, these changes have been found to extend', Lonnie Grove Petersen says.

'However, it is important to note, that we do not know if these changes are bad for the brain. We do not yet understand how these structural changes relate to functional changes. The changes are adaptations to the space environment. This is the reason we can use it to learn something about the normal physiology of the brain – and this is what we need to understand the disease development of our patients here on Earth', she says

May be significant to future space missions

Lonnie Grove Petersen and her group of researchers have spent the past decade working to identify the cause, and thus a cure, of these symptoms. And this has taught them something about one of the basic functions of the brain: the pressure regulation mechanism.

’When humans travel to space, the body experience the same pressures from head to feet.. This means that the amount of blood in the heart and possibly also the head increases compared to standing on Earth, and this affects the pressure in the brain. Unlike on Earth, where gravity is constantly pulling the blood away from the head and down towards the feet. That is why one of the first feelings experienced by astronauts in a gravity-free environment is an immense flow of blood to the head. It feels like hanging upside down on the monkey bars', she says.

The pressure regulation mechanism makes sure the brain stays put, and that the blood and brain fluid continue to circulate.

‘We have performed tests on patients during parabolic flights (short-term weightlessness on board an airplane, ed.), where a catheter in their head revealed changes to the pressure in the brain. This did not show a great increase in pressure, though. We have therefore formulated the theory that the general, equal distribution of blood and fluid results in a minor, but constant pressure on the brain, and in the long run this will affect the water circulation’, she says.

‘Here on Earth we spend most of our waking hours standing or sitting down, and at night we lie down. This creates a diurnal variation in brain pressure, but astronauts do not have that because they are weightless all the time. In a gravity-free environment, they cannot “stand up”, so to speak’, Lonnie Grove Petersen explains.

Therefore, the researchers have begun to conduct brain scans on astronauts before and after journeying into space. This has shown that the cavities in the brain holding the cerebral spinal fluid (brain fluid) grow larger.

According to Lonnie Grove Petersen, this may suggest that the amount of fluid in the brain has increased. The brain also appears to shift slightly, moving upwards in the skull. This may put pressure on some of the areas that absorb brain fluid and thus enable it to escape the brain.

‘If weightlessness affects the pressure regulation and fluid circulation mechanisms in the brain, and if this is the cause of the visual disorders, it means that the brain depends on gravity to function normally. This is new to us, and holds implication not just for astronauts, but also patients here on Earth’, she says.

Contact:

Dr. Lonnie Grove Petersen MD. PhD
+1 858 263 6365
lonnie@sund.ku.dk