# Brain scans taken before launch predicted which astronauts would lose balance on their first day home and who would recover by day four

> A pattern in astronauts' brains before launch may help predict who will struggle most with balance after returning from space, as well as who will recover more quickly during the following days. The signal comes from preflight brain connectivity in a region...

Canonical URL: https://www.argo.net/brain-scans-taken-before-launch-predicted-which-astronauts-would-lose-balance-on-their-first-day-home-and-who-would-recover-by-day-four/
Byline: ARGO.net Editorial Team
Published: 2026-08-20T20:55:02+00:00
Categories: Explainer, Space

![Intricate MRI brain scan displayed on a computer screen for medical analysis and diagnosis](https://www.argo.net/wp-content/uploads/2026/08/astronaut_brain_scan-1.jpg)

A pattern in astronauts' brains before launch may help predict who will struggle most with balance after returning from space, as well as who will recover more quickly during the following days. The signal comes from **preflight brain connectivity** in a region that helps combine inner-ear balance information with signals from vision and the body.

The [npj Microgravity study](https://www.nature.com/articles/s41526-025-00536-2), published on November 27, 2025, examined astronauts who completed missions aboard the International Space Station. Researchers compared brain scans taken before flight with demanding balance tests performed one day and four days after landing.

The results suggest that differences in brain organization may reveal how strongly each astronaut adapts to weightlessness and then readjusts to Earth's gravity. The process is called **sensory re-weighting**, because the brain changes how much attention it gives to different sources of information about motion and body position.

## A brain signal linked to postflight balance

Standing upright requires a constant stream of information. The eyes report how the surroundings are moving. Pressure and touch sensors describe contact with the ground, while the inner ear detects head motion and gravity. The brain combines these signals many times each second to maintain **balance control**.

Spaceflight changes the value of those signals. In orbit, the inner ear can still sense rotation and movement, although its gravity-sensing organs no longer receive the steady downward pull found on Earth. The brain gradually changes how it interprets the information, allowing astronauts to move and work in weightlessness.

After landing, gravity suddenly returns as a strong physical signal. The brain must restore its Earth-based way of combining sensory information. During that adjustment, astronauts can feel unsteady, especially when visual clues are removed or the head is moving.

The study abstract describes the broad problem clearly: "Exposure to microgravity results in transient sensorimotor performance declines when crewmembers return to Earth, likely due to sensory re-weighting." The research team asked whether brain scans collected before launch could forecast part of that decline.

## How microgravity changes sensory priorities

On Earth, the **vestibular system** in the inner ear helps the brain determine which way is up. Small organs filled with fluid and tiny sensory structures respond when the head tilts, accelerates or changes direction. Gravity provides a dependable reference that helps the brain interpret those movements.

Weightlessness removes that familiar reference. Signals that once indicated a tilt may have a different meaning in orbit, where astronauts can float in any direction. Vision becomes especially useful because walls, equipment and other crew members provide clues about orientation inside the spacecraft.

The brain also changes its use of touch and body-position signals. Pressure on the soles of the feet becomes less useful while floating, since the feet may rarely support body weight. Muscles and joints operate under unusual loads, adding another adjustment for the nervous system.

Once astronauts return, the old sensory rules become useful again. The brain must increase its use of gravity-related vestibular information and restore the value of pressure signals from the feet. Individual astronauts complete that process at different rates, which helps explain why some can walk steadily soon after landing while others need more time.

## Why the OP2 network stands out

The strongest predictor in the study involved a brain area called **OP2**, short for parietal operculum 2. OP2 lies within a region of the cerebral cortex associated with vestibular processing. It receives information related to the inner ear and connects with areas involved in vision, touch and movement.

Researchers studied how independently the OP2 network operated compared with other parts of the brain. They called this property **network segregation**. A highly segregated network has stronger communication within its own group of connected regions and less communication with regions outside that group.

Greater segregation can support efficient processing because specialized regions work closely together. It may also give a network room to reorganize when conditions change. For astronauts, a more clearly separated OP2 network could support a stronger adjustment to microgravity, followed by a larger aftereffect when gravity returns.

The study found that greater segregation in the right OP2 network before launch was associated with poorer performance on a difficult balance test one day after landing. Four days after landing, greater segregation in both the left and right OP2 networks was associated with better performance. Astronauts with higher right OP2 segregation also showed larger improvements between those two testing days.

## Testing astronauts before and after ISS missions

The research team used **resting-state functional magnetic resonance imaging**, often shortened to resting-state fMRI. During such a scan, a person lies still without performing a set task. The scanner records changes linked to blood flow, allowing scientists to estimate which brain regions tend to become active together.

Astronauts received scans about 180 days and 60 days before launch. Further scans were collected four days after their return, followed by sessions around 30, 90 and 180 days after landing. The repeated measurements allowed the researchers to test whether each network's segregation remained reasonably stable over a long period that included an **International Space Station** mission.

The team examined the left and right OP2 networks, along with the visual network. A network called the default mode network served as a control. The visual network had excellent reliability across the scans. The left OP2 network showed good reliability, while the right OP2 network had moderate reliability. Reliability in the control network was too low to meet the researchers' planned standard.

Balance was measured with the **Sensory Organization Test-5**. Astronauts stood with their eyes closed and their arms crossed while the support platform moved in response to their swaying. With dependable visual information removed and the floor providing less useful feedback, the test placed greater demand on vestibular processing.

A harder version, called SOT-5M, added repeated head tilts. The astronauts moved their heads forward and backward at a set rhythm while trying to remain upright. The OP2 findings appeared during this moving-head condition, which placed an added load on the brain systems that interpret vestibular signals.

## Poorer balance on day one, faster recovery by day four

The direction of the prediction changed across the first four days. Higher right OP2 segregation was linked with poorer SOT-5M balance one day after return. By day four, higher segregation in either OP2 network was linked with better balance during the same demanding task.

Researchers interpret the first result as a possible sign of strong adaptation during flight. An astronaut whose brain adjusted more fully to microgravity could experience a larger mismatch when Earth's gravity returned. A highly organized OP2 network may then help the same astronaut revise those sensory settings more rapidly.

Real crew experiences show how intense the early adjustment can feel. In a [NASA account](https://www.nasa.gov/centers-and-facilities/johnson/life-after-microgravity-astronauts-reflect-on-post-flight-recovery/) of life after microgravity, ESA astronaut Andreas Mogensen said, "With eyes closed, it was almost impossible to walk in a straight line." JAXA astronaut Satoshi Furukawa described the gradual improvement: "Day by day, I recovered and got more stable."

The study's follow-up analysis supported a similar recovery pattern. Astronauts with greater right OP2 segregation before flight showed the largest balance improvements from day one to day four. The finding connects a preflight brain measurement with the pace of early readjustment after months in microgravity.

## Preparing crews for Moon and Mars landings

Future explorers may face immediate physical demands after landing on another world. A crew arriving at the Moon could need to leave a spacecraft, move equipment and respond to unexpected problems while adapting to lunar gravity. Mars crews would face a similar challenge after spending months in weightlessness during the journey.

Such **gravitational transitions** create different sensory conditions. Lunar gravity is about one-sixth of Earth's gravity, while Mars has a little more than one-third. Astronauts will still need dependable balance and coordination even though neither environment matches the conditions used during training on Earth.

A reliable preflight predictor could help mission planners prepare support for each crew member. Astronauts expected to experience larger balance aftereffects might receive added training before launch. Mission schedules could also account for likely recovery needs during the first hours or days after landing.

The authors describe brain network segregation as a possible tool for planning **individualized countermeasures** and rehabilitation. It could also help researchers test whether artificial gravity, balance exercises or other approaches improve the nervous system's response to changing gravity.

NASA's [CIPHER program](https://www.nasa.gov/about-cipher/) takes a broad look at how the human body responds to longer missions. Research on brain function and sensorimotor performance forms part of that effort, since crews traveling farther from Earth will have less immediate medical and operational support. The **NASA Human Research Program** uses such findings to reduce risks during future exploration.

## Promising results with statistical limits

The findings remain preliminary. Astronaut studies usually involve small groups because relatively few people complete long-duration space missions and participate in every required test. A small sample makes it harder to separate a dependable biological relationship from variation that can occur by chance.

The researchers accounted for age and sex in their prediction models, along with previous flight experience. Some of those factors were also associated with balance scores. Experienced astronauts had lower right OP2 segregation before flight than first-time flyers, suggesting that earlier exposure to microgravity may have lasting links with brain network organization.

Several initial results reached the study's standard for statistical significance. After the team applied a **false discovery rate correction** for the many comparisons being tested, none of the findings remained significant. Such corrections reduce the chance that one positive result appears simply because researchers examined several possible relationships.

The results therefore provide a scientific lead that requires testing in larger astronaut groups. Future research can examine whether OP2 segregation predicts performance across different mission lengths and landing environments. Scientists can also study whether training changes the measure and whether it forecasts practical tasks such as walking, vehicle exit or work in a spacesuit.

Even with those limits, the study offers a useful view of individual adaptation. Astronauts enter space with different patterns of brain organization and those patterns may influence both the strength of their adjustment to weightlessness and the speed of their return to gravity-based movement. A clearer forecast could eventually help crews arrive on another world ready to stand, move and work safely. Broader mission context is available from [NASA's Human Research Program](https://www.nasa.gov/hrp/) and [NASA's International Space Station overview](https://www.nasa.gov/international-space-station/).