Imaging Shows Brain Changes After Space Travel

Nancy A. Melville

February 16, 2017

The brain undergoes significant changes in gray matter volume during spaceflight, including decreases in some areas but intriguing increases in others, suggest results of a novel study looking at astronauts' brain scans before and after space missions. The effects were even more pronounced after longer stays in space.

"We typically don't have the opportunity to examine such neuroplasticity in the healthy brain on earth unless we are looking at people practicing a skill for an hour a day, for example," senior author, Rachael D. Seidler, PhD, told Medscape Medical News.

"This is a compelling model of extensive brain plasticity. The work may have implications for those who are largely immobile on earth, for example those who are bed-ridden due to complications."

The study, supported by the National Aeronautics and Space Administration (NASA), was published online in December 2016 in Nature Microgravity.

For the study, considered the first to examine the effects of space travel on the structure of the brain, Dr Seidler and her colleagues were able to evaluate the structural MRI scans on 12 astronauts who spent less than 2 weeks in space as shuttle crew members and 14 who spent 6 months on the International Space Station (ISS).

The astronauts ranged in age from approximately 40 to 60 years, and mission length ranged from 12 days to less than 200 days.

Comparison of the MRIs scans obtained before and after the space missions showed extensive decreases in volumetric gray matter, notably in large areas covering the temporal and frontal poles and around the orbits of the brain, following the missions.

The effect was more pronounced among ISS astronauts than among shuttle crew members, in brain regions including the insular cortex, suggesting a greater effect with a longer duration in space.

Interestingly, there were also some small but localized increases in gray matter in sensorimotor regions specific to lower-limb control, suggesting neuroplasticity in those functions.

Because lower-limb muscles are used substantially on earth to counter the effects of gravity, they tend to display the most significant morphologic changes in space, the authors note.

"Increasing GM [gray matter] volume in the brain regions which process lower limb somatosensory inputs and motor control may reflect an attempt by the system to increase input sensitivity of representations and adaptation of lower limb control to the microgravity environment," they write.

The gray matter volume changes overlapped with changes in cerebral spinal fluid (CSF) volume, suggesting effects of CSF redistribution in a zero-gravity environment that is similar to the effects seen in research of long-duration head-down-tilt bed rest, which suggests gray matter changes attributed to an upward shift of the brain's center of mass within the skull.

Such findings may help in the understanding of conditions such as normal-pressure hydrocephalus, in which the accumulation of CSF in areas of the brain increases pressure.

Noting that an important limitation of the study is that the analysis involved only one preflight and one postflight MRI scan, Dr Seidel said her ongoing research with NASA — The Spaceflight Effects on Neurocognitive Performance: Extent, Longevity, and Neural Bases (NeuroMapping) study — is focusing on more detailed, prospective data to include cognitive information.

"I am currently conducting a prospective study with multiple timepoints to look at recovery postflight, and multiple cognitive and sensorimotor assessments to understand the behavioral implications," she said.

Resilience, Recovery

Commenting on the study, Glenn D. Graham, MD, PhD, deputy national director for neurology in specialty care services at the Veterans Affairs Central Office, in Washington, DC, said the findings, though clearly preliminary, offer some encouraging signs in terms of resilience and recovery after spaceflight.

"I found it interesting that there were no differences, for instance, in gray matter loss between those who were on first-time missions and those who had previous in-flight experience," he told Medscape Medical News.

"That's reassuring because it suggests the effects to the brain are not irreversible. If they were, you would expect the effects to be worse with subsequent missions."

He added that until more data are available, it's hard to interpret the implications of the changes in gray matter volume.

"The loss in gray matter volume doesn't necessarily mean brain cells have died or atrophied," he explained. "It could suggest there is more fluid or redistribution of fluid, or more intracranial pressure, so it's hard to say."

One certainty, however, is the striking fact that humans can survive in space at all, considering their evolution within the earth's atmosphere, Dr Graham noted.

"All of life on the planet has evolved within the world's gravitational field, so the fact that you can put humans in a zero-gravity environment and it wouldn't be fatal to them is kind of remarkable," Dr Graham said.

"It's remarkable that there isn't some process that absolutely depends on gravity to function, just as there are processes that depend on oxygen."

Further intriguing insights on the effects of space travel are expected soon from another prominent NASA study: the Twins Study. This study is comparing data on NASA astronaut Scott Kelly, who was on the ISS for nearly a year, with those from his identical twin brother, Mark Kelly, who remained on Earth.

While research articles on a multitude of physiologic effects on the twin brothers are still in progress, some early findings from an analysis focusing on cognitive performance indicate that Scott had a slight decrease in cognitive speed and accuracy after 12 months compared with findings after a 6-month mission. However, the difference does not represent a relevant change in cognitive performance, NASA reported.

Another study showed that Scott had altered lipids, indicating inflammation, upon return compared with his Earth-bound brother, and his telomeres, which usually decrease in length with age, in fact increased in space.

NASA reported that the change could be associated with increased exercise and reduced caloric intake during the mission.

A joint summary of the study is planned to be released later in 2017.

The study was supported by a grant from NASA. The authors and Dr Graham have disclosed no relevant financial relationships.

Nature Microgravity. Published online December 19, 2016. Abstract

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