# Five astronauts carried resting-state brain recordings through long missions in orbit and the study found weaker alpha activity in a key resting network during flight, with some links still below preflight levels 20 days after landing

> Future crews heading far from Earth will need sharp judgment, steady attention and brain systems that can keep adapting when gravity disappears for months. A small astronaut study now suggests that some of the brain's quiet resting patterns change in orbit and...

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Byline: ARGO.net Editorial Team
Published: 2026-08-12T20:40:02+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.jpg)

Future crews heading far from Earth will need sharp judgment, steady attention and brain systems that can keep adapting when gravity disappears for months. A small astronaut study now suggests that some of the brain's quiet resting patterns change in orbit and do not fully rebound within the first few weeks back on Earth.

A [Scientific Reports study](https://doi.org/10.1038/s41598-023-34744-1) tracked **resting-state EEG** in **five astronauts** before flight, during long missions and again after landing. The researchers focused on the brain's **default mode network**, a set of regions active during quiet wakeful rest and found lower **alpha-band power** during flight as well as after return. Some measures of network coupling also remained weaker up to **20 days after landing**.

The result does not say astronauts were cognitively impaired in a simple, direct way. It does show that long exposure to **microgravity** leaves a measurable signature in brain activity and that recovery is still underway nearly three weeks after touchdown. For mission planners, that matters because crews on future lunar and Mars operations may have to make hard decisions soon after arrival, when their nervous systems are still readapting.

## What the EEG recordings showed in orbit

The study used electroencephalography, or EEG, to measure the electrical rhythms produced by the brain at rest. Each astronaut completed tests in three broad phases: before launch, during the mission and after return to Earth. The team separated **eyes-closed** and **eyes-open** recordings, which gave them two ways to check whether the same signal held up across slightly different resting conditions.

The clearest result was a drop in alpha activity inside the default mode network. In the eyes-closed condition, the reduction during flight and after flight was highly significant. In the eyes-open condition, the drop was smaller, yet it still appeared during flight and remained present after landing. Alpha rhythms are often linked with large-scale coordination during relaxed wakefulness, so a sustained reduction suggests that the resting brain was working under a different balance in orbit than it did before launch.

The researchers also estimated **functional connectivity**, which is a way of asking how strongly parts of a network move together over time. Connectivity strength fell during flight in both recording conditions. After landing, the eyes-open measure still showed a significant reduction compared with preflight levels, while the eyes-closed postflight connectivity result no longer reached significance. That pattern points to partial recovery rather than a full reset.

## Why alpha power and connectivity matter for astronauts

Quiet brain activity can sound less important than performance during a demanding task, yet resting networks help set the background state from which attention, memory and self-monitoring operate. The **default mode network** is especially interesting in space medicine because it supports internal mentation and shifts in mental focus, both of which are needed during long missions with heavy operational demands.

Researchers chose the alpha band because earlier work has tied it to broad coordination across brain regions. A weaker alpha pattern in orbit may reflect the nervous system adjusting to altered balance cues, fluid shifts, changed sleep timing and the unusual sensory environment of spaceflight. The paper does not isolate one cause, but it does show that the altered state can be detected with repeated EEG recordings.

An accessible summary posted by the [Global Brain Health Institute](https://www.gbhi.org/news-publications/effects-spaceflight-eeg-alpha-power-and-functional-connectivity) repeats the study's main abstract and underlines the operational idea behind the work: a periodic EEG check might someday help crews and flight surgeons watch for changes in **cerebral functional integrity**. That remains a future use case rather than a current medical standard, though the study gives a concrete reason to keep testing the idea.

Another practical point comes from the method itself. EEG is lighter and more portable than many imaging tools, which makes it more realistic for missions where mass, time and crew workload stay tightly constrained. If a simple recording can flag a slow return toward baseline, agencies could eventually use it alongside behavioral tests to decide when a returning crew member is ready for the next demanding task.

## Recovery was still incomplete 20 days after landing

The most striking phrase in the abstract is the timescale. The reduction in default mode network alpha power, along with weaker connectivity strength in some comparisons, persisted until **20 days after landing**. A three-week recovery window may sound short in ordinary life, yet it is long enough to matter when a mission timeline expects rapid surface work, piloting, equipment checks, or emergency response soon after arrival.

The postflight pattern also helps separate immediate readaptation from longer recovery. Astronauts often report balance and orientation problems right after return because the brain must reweight signals from the inner ear, vision and body motion. This EEG study suggests that readaptation is not only about obvious dizziness or postural control. Some of the quieter background organization of the brain still looked different well after the first landing day had passed.

NASA's [Neuroscience Laboratory](https://www.nasa.gov/reference/jsc-human-research-laboratories/) treats changes in the nervous system as an operational problem because they can affect posture, orientation and other critical tasks during g-state transitions. The new EEG paper adds one more piece to that picture. Return to Earth starts recovery, yet the process is still ongoing at day 20 for at least some resting-state measures.

Small sample size remains an important caution here. Human spaceflight studies rarely have large numbers and this one included only five astronauts. The repeated design strengthens the evidence because each person was tracked across multiple mission phases, but the findings still need confirmation in larger crews and in a broader mix of ages, sexes, mission lengths and operational roles.

## Other brain studies point to the same broad concern

This EEG paper does not stand alone. A 2023 [Cerebral Cortex study](https://academic.oup.com/cercor/article/33/6/2641/6608960) followed 15 astronauts across about six months of spaceflight and found changes in task-based brain connectivity during a spatial working memory test, even though performance itself stayed largely stable. That combination is important because it suggests the brain can preserve outward task success while its supporting networks reorganize behind the scenes.

Earlier reporting from the [Medical University of South Carolina](https://www.musc.edu/content-hub/news/2019/10/30/brain-changes-in-space-missions) described another line of evidence: brain structure changes in NASA astronauts that correlated with postflight cognitive and motor measures. That work focused on MRI rather than EEG and it involved a different study design, yet it supports the same broad message that long missions affect the human brain in ways that deserve close monitoring.

Taken together, these studies suggest that spaceflight affects the brain across several levels at once. One set of experiments detects structural shifts, another sees changed connectivity during tasks and the new EEG paper identifies altered resting rhythms. Each method captures a different piece of the same adaptation problem. Long missions ask the nervous system to operate in an environment it did not evolve for and the measurable adjustments continue after the crew comes home.

The consistency across methods also argues against treating any single astronaut symptom as the whole story. A crew member may perform well on a given task while still carrying altered background connectivity, or may show structural change without a dramatic immediate complaint. Multi-method monitoring therefore looks more useful than any single test when agencies plan for deep-space expeditions.

## What mission planners can take from a five-astronaut study

The paper's most useful contribution may be operational rather than dramatic. It shows that **brain network monitoring** can detect persistent changes with a compact, repeatable method. For exploration programs, that supports building recovery margins into schedules and continuing follow-up beyond the first few days after landing. Missions to the Moon or Mars will put greater weight on that question because the crew may need to work in unfamiliar gravity soon after arrival.

The study also shows why postflight timing matters. If brain rhythms and some network links are still below baseline at day 20, then assessments taken only right after landing may miss part of the adaptation curve, while a single later assessment may miss the steepest early changes. Repeated measurements could reveal which patterns rebound quickly and which ones recover more slowly.

Even so, the evidence remains early. The study does not prove that a given EEG shift predicts a specific operational failure and it does not separate the effects of microgravity from every other stressor of spaceflight. Sleep disruption, workload, carbon dioxide exposure and mission duration may all contribute. What the paper does provide is a measured starting point: **long-duration spaceflight** changed resting brain activity in a small astronaut group and part of that change was still visible weeks later.

Future studies will need more astronauts, tighter links between EEG and performance and longer follow-up after return. If those data arrive, the field may move from describing adaptation toward forecasting it. For now, the five-person study offers a grounded warning for exploration medicine: the brain comes home with the astronaut, but some of its resting networks are still readjusting after the capsule opens.