astronaut in space

Structural changes observed in the brains of astronauts on long-duration missions

Image credit: Dreamstime

Major changes in the brains of astronauts who have endured long durations in space have been observed by researchers from Oregon Health & Science University.

The team imaged the brains of 15 astronauts before and after extended tours of duty on the International Space Station (ISS). They found that in their time away from planet Earth, the fluid-filled spaces along veins and arteries in the brain were altered.

These spaces, known as perivascular space, are integral to a natural system of brain cleansing that occurs during sleep. The network of tubes is known as the glymphatic system – a brain-wide network that clears metabolic proteins that would otherwise build up in the brain. Scientists say this system seems to perform optimally during deep sleep.

“These findings have important implications as we continue space exploration,” said senior author Juan Piantino. “It also forces you to think about some basic fundamental questions of science and how life evolved here on Earth.”

Researchers used magnetic resonance imaging to measure perivascular space in the brains of astronauts prior to their launch and again immediately after their return. They also took MRI measurements again at one, three and six months after they had returned. Astronauts’ images were compared with those taken of the same perivascular space in the brains of 16 Earth-bound control subjects.

Comparing before and after images, they found an increase in the perivascular spaces within the brains of first-time astronauts, but no difference among astronauts who previously served aboard the space station orbiting Earth.

“Experienced astronauts may have reached some kind of homeostasis,” Piantino said. 

In all cases, scientists found no problems with balance or visual memories that might suggest neurological deficits among astronauts, despite the differences measured in the perivascular spaces of their brains.

In comparing a large group of deidentified astronauts, the study is the first to comparatively assess an important aspect of brain health in space.

Human physiology is based on the fact that life evolved over millions of years while tethered to Earth’s gravitational pull. Unbound by the forces of gravity, the normal flow of cerebrospinal fluid in the brain is altered in space.

“We all adapted to use gravity in our favour,” Piantino said. “Nature didn’t put our brains in our feet – it put them high up. Once you remove gravity from the equation, what does that do to human physiology?”

The perivascular spaces measured in the brain amount to the underlying 'hardware' of the glymphatic system. Enlargement of these spaces occurs in ageing, and also has been associated with the development of dementia.

“These findings not only help to understand fundamental changes that happen during space flight, but also for people on Earth who suffer from diseases that affect circulation of cerebrospinal fluid,” Piantino added.

In 2019, another study found that most astronauts who spend more than a month in space developed neuro-ocular syndrome, which can significantly change the shape of their eyeballs.

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