Nasa may need to invent a spaceship with artificial gravity before humans can venture to Mars, after a new study found weightlessness causes worrying changes in the brain.

The mission would be fraught with technical challenges, but the real difficulties may lie in getting astronauts there with their minds intact.

Alarming new research, funded by Nasa, has found that microgravity causes astronauts' brains to shift upwards and become squashed at the top of the skull, piling pressure on vital neural regions.

Space travel is not good for the human brain.

Crucially, the parts of the brain most affected - the frontal and parietal lobes - control movement and higher executive function, which are essential for attention, focus, planning, organising and remembering details. They are also the regions linked to pro-social behaviour, which help people avoid making hurtful or inappropriate comments.

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Researchers at the Medical University of South Carolina (MUSC) said urgent work was needed to gauge the impact of brain damage and find out how long it lasted after a mission, particularly as companies are already planning on taking civilians into space.

NASA Nevermind setting up human colonies on Mars, getting there in the first place is going to be hard.

Dr Michael Antonucci, at the department of radiology and radiological science at MUSC, said: "Any change to a region of the brain that controls the way we sense our environment and our ability to interact with it raises concerns. There are some medications that are used to treat patients with increased pressure on earth. However, how these would work in microgravity is uncertain. Designing a space vehicle with artificial gravity might be a way of minimising changes."

Although artificial-gravity still lies firmly in science fiction, theoretically, spinning a space station would create enough centrifugal force to create the effect of being pinned to the surface.

For this study, the team examined the brains of participants who stayed in bed for 90 days, and were required to keep their heads tilted downwards to simulate the effects of microgravity.

They also checked brain scans from 18 astronauts who spent a few weeks aboard Nasa's space shuttle, and compared them with 16 astronauts who had spent an average of three months in the International Space Station.

Brain scans showed a narrowing of the bumps and depressions in the brain folds in the bed-ridden participants, 94 per cent of the ISS astronauts, but only 18 per cent of the shuttle crews. There was also evidence of brain shifting up into the inner roof of the skull.

A journey to Mars can take three to six months, and crews would be expected to stay for two years until planetary alignment allowed for a journey home. It means crews would be in reduced gravity for around three years.

To date, the longest continuous time in space was 438 days, a record held by Russian cosmonaut Valery Polyakov.

The research was published in the New England Journal of Medicine.