New York, Feb 1 (IANS): Astronauts' brains compress and expand during spaceflight, show results of brain scans before and after space missions.

The researchers examined structural MRIs in 12 astronauts who spent two weeks as shuttle crew members, and 14 who spent six months on the International Space Station.

All experienced increases and decreases in gray matter in different parts of the brain, with the changes more pronounced the longer the astronauts spent time in space, according to the study published in the journal Nature Microgravity.

"We found large regions of gray matter volume decreases, which could be related to redistribution of cerebrospinal fluid in space," said principal investigator Rachael Seidler, Professor at University of Michigan in the US.

"Gravity is not available to pull fluids down in the body, resulting in so-called puffy face in space. This may result in a shift of brain position or compression," Seidler noted.

The researchers also found increases in gray matter volume in regions that control leg movement and process sensory information from legs, which may reflect changes related to the brain learning how to move in microgravity.

These changes were greater in space station astronauts because their brains were learning and adapting all the time.

"It's interesting because even if you love something, you won't practice more than an hour a day," Seidler said.

But the brain changes researchers observed were equivalent to someone practicing a new skill round-the-clock.

"In space, it's an extreme example of neuroplasticity in the brain because you're in a microgravity environment 24 hours a day," Seidler said.

Seidler said the brain changes could reflect new connections between neurons.

"The behaviour may return to normal, but the way the brain controls the behaviour may change," she said.

The findings may lead to new ways of thinking about certain health conditions -- for example, people on long-duration bed rest or people who have normal pressure hydrocephalus, a condition in which cerebrospinal spinal fluid accumulates in ventricles in the brain and causes pressure.