The effects of long-term space travel on humans are only beginning to be understood:

In a new study, a collaborative effort between the European Space Agency and Russia’s space agency Roscosmos, researchers have explored how cosmonauts’ brains change after traveling to space and back. And they showed how the brain adapts to spaceflight, finding that the brain is almost “rewired,” and both fluid shifts and shape changes occur. These changes can last for months after a person returns to Earth, the researchers found.

The strange brain changes that the team observed were “very new and very unexpected,” study lead Floris Wuyts, a researcher at the University of Antwerp in Belgium, told Space.com.

Chelsea Gohd, “Cosmonaut brains are ‘rewired’ by space missions, scientists find” at Space.com (February 18, 2022)

These changes, while they may help the brain adapt to microgravity (weightlessness compared to Earth), seem to persist for months after the astronauts return. The paper referred to is open access.

The researchers looked at the brains of twelve cosmonauts after their return to Earth and found “significant microstructural changes” in their brains’ white matter, which connects systems together and transmits signals:

The data were obtained through diffusion magnetic resonance imaging (dMRI) scans taken just before and right after the time participants spent in space, which lasted an average of 172 days. Further scans were carried out seven months later, and while there was a reversal of some changes, a few of them were still visible.

Specifically, the team found changes in neural tracts related to sensory and motor functions, and speculate this could have something to do with the cosmonauts’ adaptation to life in microgravity.

“Considering the different physics and kinesthetics applying to the extreme environment of space and the hypothesis that these have significant effects on the brain’s representation and control of the body, these tracts are therefore suspected to reflect this altered sensorimotor function shown in space travelers,” the team writes.

David Nield, “Signs of ‘Significant’ Brain Rewiring Have Been Found in Space Travelers” at ScienceAlert (February 21, 2022) The paper is open access.

Sponsors of space probes are monitoring the situation:

NASA has been studying what happens to the human body in space for over 50 years. Studying the effects of space flight on human bodies can help prepare astronauts for long-term destinations, like the moon and Mars, according to a statement. This research could potentially allow scientists to protect astronauts’ brains further while traveling through space, per Space.com.

Elizabeth Gamillo, “Long-Term Space Travel May ‘Rewire’ Astronauts’ Brains” at Smithsonian Magazine (February 24, 2022) The paper is open access.

The researchers offer “Humans undergo extreme physiological changes when subjected to long periods of weightlessness, and as we continue to become a space-faring species, it is imperative that we fully understand the physiological changes that occur in the human body, including the brain.” So far, no one is suggesting that it’s a reason to not “boldly go,” in the iconic directive in Star Trek.

But then Star Trek was dealing with fictional extraterrestrial intelligences, not the mundane things that happen when our bodies get shot into space, that we must compensate for.

You may also wish to read: Interstellar travel: The four top technologies for getting there. Astrophysicist Adam Frank looks at the technologies we meet in science fiction and identifies the challenges that hold them back. In a world where technology must confront fundamental physics, what are the chances and obstacles for cryosleep, light sails, wormholes, and warp drives?

and

Researchers still puzzled: Why did human brains shrink? Human brain volumes decreased by 10% in the last 40,000 years, coinciding with spectacular intellectual achievements. Examples of brain shrinkage among animals are fascinating but have not provided much insight. But perhaps we should ask, how much does brain size even matter?