What happens to the brain in space? Every astronaut brain study
Brain scans and thinking tests of astronauts, cosmonauts and space tourists, from 1998 to 2026: how the brain moves, how its fluid spaces grow, whether it recovers, and whether astronauts think any worse.
By Leon Falkner, Data & Research Analyst · Reviewed by Aarav Vardhan, Editor-in-Chief · Published 2 November 2026 · 9 min read
About this study
- Report type
- Data study of published research
- Data
- 41 peer-reviewed studies, 59 rows by measure; NASA selection counts
- People
- Astronauts, cosmonauts and space tourists; a median of 13 per study
- Years
- 1998 to 2026
- Licence
- CC BY 4.0 (our dataset and charts)
- Version
- 2026.11
- Sources
- 55
Space changes where the brain sits and how much fluid surrounds it; it has not been shown to lower how well astronauts think. In 41 studies of astronauts and cosmonauts (1998-2026), the brain’s fluid spaces grew about 12% to 24% over a 6-month mission and were only about half back 7 months later; after a year in space the top of the brain sat up to 2.5 mm higher. Thinking tests show a small dip early in flight and no lasting drop. IQ Metrics Research, November 2026.
01 Key findings
- The brain’s fluid spaces grow by about a sixth. After about 6 months in space the ventricles were 11.6% larger in 11 cosmonauts, and the lateral ventricles 17% (left) and 24% (right) larger in 10 NASA astronauts.Van Ombergen et al. 2019; Hupfeld et al. 2020
- They are only about half back after 7 months. The cosmonauts’ ventricles were still 6.4% larger; in 11 NASA astronauts, brain plus fluid volume was still 28 mL up a year after landing.Van Ombergen et al. 2019; Kramer et al. 2020
- The brain moves up inside the skull: after a year in space, the area at the top that plans movement sat 2.52 mm higher. Most of the shift reverses within 6 months of landing.Wang et al. 2026 (PNAS)
- No lasting drop in thinking. 25 astronauts were about 0.31 standard deviations slower early in flight, then back to their usual speed after landing; the study found “no evidence for a systematic decline”.Dev et al. 2024
- Up to half develop eye changes: 21 of 37 NASA astronauts (56.7%) developed SANS, the swelling at the back of the eye linked to the same fluid shift.McGregor et al. 2025
- It is harder to get in than to get changed: NASA’s 2025 class took 10 people from more than 8,000 applicants, about 1 in 800; in 2017 it was 1 in 1,525.NASA
02 Statistics to quote
Growth of the brain’s fluid-filled ventricles after about 6 months in space (11 cosmonauts).
Van Ombergen et al. 2019Still larger than before flight about 7 months after landing.
Van Ombergen et al. 2019Upward shift of the top of the brain after a year in space.
Wang et al. 2026NASA astronauts who developed eye and optic-nerve changes (SANS) on their mission (21 of 37).
McGregor et al. 2025Peer-reviewed studies of the brain or thinking of people who flew in space, 1998 to 2026.
IQ Metrics countOdds of being chosen for NASA’s 2025 astronaut class (10 from more than 8,000).
NASA03 What happens to an astronaut's brain in space?
Without gravity, body fluids shift toward the head. Brain scans before and after flight show the result: the brain sits higher in the skull, the fluid-filled spaces inside it grow, and in many astronauts the back of the eye swells [1] [3] [7]. We collected 41 peer-reviewed studies from 1998 to 2026: 28 of NASA astronauts, 8 of Russian cosmonauts, 3 of both and 2 of space tourists.
What 41 studies found in the brains of people who flew in space
Findings by what was measured and what a later check showed (59 findings: a study that measured several things counts once for each). Most changes were measured only once, days after landing ("Not re-checked"; on phones "Once"); few studies checked again months later. Every study is in the table below.
Source: Our dataset of 41 studies, 1998-2026 (CSV below); every study is in the table and the source list
Data table
| what was measured | Back to normal | Still partly there | Not re-checked | No change found |
|---|---|---|---|---|
| Brain position and shape | 0 | 1 | 3 | 0 |
| Fluid spaces (ventricles) | 0 | 4 | 8 | 0 |
| Grey matter | 0 | 1 | 4 | 0 |
| White matter | 0 | 2 | 2 | 1 |
| Spaces around blood vessels | 0 | 0 | 2 | 1 |
| Brain activity and wiring | 2 | 1 | 5 | 0 |
| Eyes and optic nerve (SANS) | 0 | 1 | 7 | 3 |
| Thinking tests | 2 | 1 | 3 | 4 |
| Blood markers of brain injury | 0 | 1 | 0 | 0 |
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Most changes were measured only once, a few days after landing, so for most of them no one yet knows if they fade. The studies are small: a median of 13 people, because only a few dozen astronauts fly long missions each decade.
04 How much do the brain's fluid spaces grow?
By about a sixth over a 6-month mission. In 11 cosmonauts the ventricles grew 11.6% [3]; in 10 NASA astronauts the lateral ventricles grew 17% and 24% [5]. Of two astronauts who stayed a year, one grew 25% and the other 2%, so time is not the whole story. Most of the growth happens in the first 6 months and tapers after [6]. On Earth, ventricles also grow slowly with age: 2.23% a year in matched adults, against 6.86% a year in astronauts across the years that included their flight [4].
How much the fluid spaces in the brain grew in space
Change in the volume of the ventricles (fluid-filled spaces deep in the brain) from before flight to just after landing. Cosmonauts: 11 people, about 6 months; NASA astronauts: 10 people, about 6 months, and two who stayed about a year, shown one by one with their permission.
Source: Van Ombergen et al. 2019 [3]; Hupfeld et al. 2020 [5]
Data table
| label | value |
|---|---|
| Cosmonauts: all ventricles | 11.6 |
| Cosmonauts: lateral ventricles | 13.3 |
| NASA, 6 months: left lateral ventricle | 17 |
| NASA, 6 months: right lateral ventricle | 24 |
| NASA, 1 year: astronaut A (left) | 25 |
| NASA, 1 year: astronaut B (left) | 2 |
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05 Does the brain go back to normal after landing?
Partly, and slowly. Seven months after landing the cosmonauts’ ventricles were still 6.4% larger than before flight [3], and in 11 NASA astronauts brain plus fluid volume was still 28 mL up 360 days after landing [2]. Crew with less than 3 years between flights showed little or no further ventricle growth on the next flight, which suggests the brain needs about that long to recover [6].
Do the fluid spaces shrink back after landing? Only halfway in 7 months
Cosmonauts' ventricle volume, percent above their own volume before flight: just after landing (11 people) and about 7 months later (the 7 who were scanned again).
Source: Van Ombergen et al. 2019 [3]
Data table
| x | Lateral ventricles | All ventricles | Third ventricle |
|---|---|---|---|
| Before flight | 0 | 0 | 0 |
| Just after landing | 13.3 | 11.6 | 10.4 |
| 7 months later | 7.7 | 6.4 | 4.7 |
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06 Does the brain move inside the skull?
Yes. In 17 of 18 astronauts after long missions, the groove at the top of the brain (the central sulcus) narrowed as the brain moved up [1]. A 2026 study of 26 astronauts and 24 people on Earth kept in a head-down bed measured it: the brain moved up and back in proportion to time in space, most in the areas for movement and the senses. After a year in space the top of the brain sat 2.52 mm higher; most of the shift reversed within 6 months, but not all [22]. Bigger shifts in one sensing area went with bigger balance problems after landing.
07 Do astronauts think more slowly in space?
A little, early in a mission. On NASA’s 10-test Cognition battery, 25 astronauts were 0.31 standard deviations slower early in flight than before it, a small change that faded; after landing their speed was back to normal, and the study found “no evidence for a systematic decline” [32]. Another group of 15 kept their thinking performance in flight and after landing while their balance fell [33]. A cosmonaut tested 29 times over 438 days on the Mir station showed no lasting impairment [38].
Thinking speed and accuracy of 25 astronauts, before, during and after 6 months in space
Average scores on NASA's 10-test Cognition battery, as z-scores corrected for practice (0 = the group's usual level; -0.3 = 0.3 standard deviations slower). Speed dipped early in flight and came back; accuracy drifted down a little, with no phase significantly different from another.
Source: Dev et al. 2024, Table 2 [32]
Data table
| x | Speed | Accuracy |
|---|---|---|
| Before flight | -0 | -0 |
| Early flight | -0.3 | -0.1 |
| Late flight | -0.2 | -0.1 |
| Early after landing | -0.1 | -0.2 |
| Late after landing | -0 | -0.2 |
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Short flights look similar: four civilians on a 3-day flight were slower on 4 of 10 tests in orbit, but “largely unaffected” overall, and back to normal after landing on all but one test [40]. Reaction-time tests are the most sensitive here; see how reaction time is measured and what processing speed says about IQ.
08 Do astronauts lose IQ in space?
No study has given astronauts an IQ test before and after flight; NASA uses shorter thinking tests instead. The one case with a lasting dip is the NASA Twins Study: after 340 days in space, Scott Kelly was slower and less accurate on landing than before, and stayed below his usual level for up to 6 months [39]. That was one person, and the authors point to the stress of returning to Earth as a possible cause. Practice also lifts scores on repeated tests, which is why the 25-astronaut study corrected for it; see what practice changes on a cognitive test.
Measure your own reasoning
Our IQ test times your reasoning on pattern puzzles and places your result against adults, with a percentile.
Take the IQ test09 Why do astronauts' eyes change?
The same fluid shift presses on the back of the eye and the optic nerve, which links the eye to the brain. NASA calls it spaceflight-associated neuro-ocular syndrome (SANS). 21 of 37 NASA astronauts (56.7%) developed it on their mission [7]; other studies, with stricter definitions, found a third [8] [27]. In a questionnaire of about 300 astronauts, 60% on long missions reported worse near or far vision [28].
How many astronauts get eye and optic-nerve changes (SANS)?
Share of astronauts in each study with the change named. The numbers differ because the studies count different things, from any sign of swelling to changes a doctor would act on.
Source: [28] [7] [8] [27] [29] [1]
Data table
| label | value |
|---|---|
| Reported worse eyesight on long missions (questionnaire, about 300 astronauts) | 60 |
| Developed SANS on the mission (21 of 37 NASA astronauts) | 56.7 |
| Clinical signs of SANS (8 of 24 NASA astronauts) | 33.3 |
| Met the SANS criteria (4 of 12 astronauts) | 33.3 |
| Flattened back of the eye (7 of 27 astronauts) | 26 |
| Swollen optic disc (3 of 18 long-mission astronauts) | 16.7 |
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10 How hard is it to become a NASA astronaut?
Very. NASA chose 10 candidates from more than 8,000 applicants in 2025, about 1 in 800 [44]; the 2017 class drew a record of more than 18,300 for 12 places, about 1 in 1,525 [46]. In 1978, the first Space Shuttle class, it was about 1 in 229 [48]. NASA has chosen 370 candidates since 1959 [44]; counting every country and every tourist, 787 people have been launched above 80 km [43].
How hard is it to become a NASA astronaut? Applicants for each place
Applicants divided by candidates chosen, for every NASA class with a published applicant count. 1990 and 1992 count only qualified applicants; recent years say "more than", so the odds were at least this long.
Source: NASA releases and history pages [44] [45] [46] [47] [49] [50] [51] [52] [53] [54] [55] [48]
Data table
| label | value |
|---|---|
| 1965 | 67 |
| 1967 | 84 |
| 1978 | 229 |
| 1984 | 290 |
| 1990 | 85 |
| 1992 | 108 |
| 1994 | 156 |
| 1996 | 69 |
| 2009 | 389 |
| 2013 | 750 |
| 2017 | 1525 |
| 2021 | 1200 |
| 2025 | 800 |
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11 How much research is there on the brain in space?
Little, but growing fast. 35 of the 41 studies came out in 2019 or later, as MRI scans before and after flight became routine. More on the brain itself: brain statistics, fact-checked and at what age the brain is sharpest.
Studies of the brain in space, by who flew
Peer-reviewed studies in our dataset by year of publication. Most are recent: MRI studies of astronauts took off after 2016.
Source: Our dataset (CSV below)
Data table
| years | NASA astronauts | Russian cosmonauts | Astronauts and cosmonauts | Space tourists (commercial) | total |
|---|---|---|---|---|---|
| 1998-2015 | 2 | 1 | 0 | 0 | 3 |
| 2016-2018 | 2 | 1 | 0 | 0 | 3 |
| 2019-2020 | 4 | 3 | 0 | 0 | 7 |
| 2021-2022 | 5 | 1 | 1 | 0 | 7 |
| 2023-2024 | 7 | 2 | 0 | 2 | 11 |
| 2025-2026 | 8 | 0 | 2 | 0 | 10 |
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12 Every study in our dataset
Every study in our dataset (41)
People = astronauts or cosmonauts who flew (many take part in several studies). Main finding = the first measure; the CSV has one row per measure. "Back to normal?" = whether a later check found the change gone.
| Roberts et al. [1] | 2017 | 34 | Astronauts | mixed | Brain position and shape; Eyes and optic nerve (SANS); Fluid spaces (ventricles) | Central sulcus narrowed in 17 of 18 astronauts after long ISS stays vs 3 of 16 after short shuttle flights; cine MRI showed an upward brain shift after all 12 long-duration cases and none of 6 short-duration cases | Not checked |
| Kramer et al. [2] | 2020 | 11 | Astronauts | long-duration | Brain position and shape; Fluid spaces (ventricles); White matter | Pituitary dome flattened in 6 of 11 astronauts; average midline pituitary height fell from 5.9 to 5.3 mm | Not fully |
| Warthen et al. [21] | 2025 | 13 | Astronauts | about 6 months | Brain position and shape; Fluid spaces (ventricles) | Brain tissue moved up inside the skull after about 6 months in space | Not checked |
| Wang et al. [22] | 2026 | 26 | Astronauts | mixed | Brain position and shape | Brain shifted backward and upward inside the skull after spaceflight, in proportion to time in space; top-of-brain regions moved most; vertical position recovered by 6 months, backward shift only partly | Partly |
| Van et al. [3] | 2019 | 11 | Cosmonauts | about 6 months | Fluid spaces (ventricles) | Ventricles were larger right after a 6-month flight and had not fully shrunk back 7 months later | Partly |
| Roberts et al. [4] | 2021 | 18 | Astronauts | about 6 months | Fluid spaces (ventricles) | Ventricles grew faster in ISS astronauts than normal ageing: 6.86% a year vs 2.23% in matched adults | Not checked |
| Hupfeld et al. [5] | 2020 | 12 | Astronauts | mixed | Fluid spaces (ventricles) | Lateral ventricles grew about 17-24% after 6 months; one of two 12-month astronauts grew 25% (left) and 23% (right), the other 2% and 3%; little recovery by 6 months after landing | Not fully |
| McGregor et al. [6] | 2023 | 30 | Astronauts | mixed | Fluid spaces (ventricles); Grey matter; White matter | Longer missions grew the right lateral and third ventricles more, mostly in the first 6 months; astronauts with under 3 years between flights showed little or no enlargement | Not checked |
| McGregor et al. [7] | 2025 | 37 | Astronauts | mixed | Eyes and optic nerve (SANS); Fluid spaces (ventricles) | Women showed a larger loss of extracellular water around the top of the brain than men | Not checked |
| Barisano et al. [8] | 2022 | 37 | Mixed | about 6 months | Eyes and optic nerve (SANS); Fluid spaces (ventricles); Spaces around blood vessels | Lateral ventricles enlarged and the CSF space at the top of the brain shrank after about 6 months on the ISS; both crews similar; no change after 2-week shuttle flights | Not checked |
| Jillings et al. [10] | 2020 | 11 | Cosmonauts | about 6 months | Fluid spaces (ventricles); Grey matter; White matter | CSF fraction rose in the lower brain and ventricles and fell below the top of the brain after 6 months in space; at 7 months whole-brain differences from preflight had mostly gone | Not fully |
| Lee et al. [12] | 2019 | 15 | Astronauts | mixed | Fluid spaces (ventricles); White matter | Extracellular water rose in frontal, temporal and occipital lobes and fell at the back of the top of the brain, by about 2.5% to 4.0% across regions | Not checked |
| Tang et al. [24] | 2026 | 13 | Mixed | long-duration | Eyes and optic nerve (SANS); Fluid spaces (ventricles) | Third-ventricle growth after long flights tracked eye-globe changes but not optic-nerve-sheath changes | Not checked |
| Koppelmans et al. [11] | 2016 | 27 | Astronauts | mixed | Grey matter | Grey-matter volume fell across the temporal and frontal poles and around the eyes after flight (larger after ISS than shuttle) and rose in the leg area of the sensorimotor cortex | Not checked |
| Batool et al. [26] | 2025 | 17 | Astronauts | about 6 months | Grey matter | Left hippocampus lost volume over a 6-month ISS mission, more than expected from ageing | Not checked |
| Tang et al. [23] | 2026 | Mixed | long-duration | Grey matter | Machine-learning brain age came out about 0.84 years higher right after flight than before, in cosmonauts | Not checked | |
| Doroshin et al. [13] | 2022 | 12 | Cosmonauts | about 6 months | White matter | Fibre tracts in the corpus callosum, arcuate fasciculus, corticospinal and cerebellar tracts changed after 6 months; many changes were still present at 7 months | Partly |
| Hupfeld et al. [9] | 2022 | 15 | Astronauts | about 6 months | Eyes and optic nerve (SANS); Spaces around blood vessels | First-time astronauts showed more perivascular-space volume after flight; experienced astronauts did not | Not checked |
| Burles et al. [25] | 2024 | 16 | Astronauts | about 6 months | Spaces around blood vessels | Small brain bleeds (microbleeds) seen in 6 of 16 astronauts before flight; no significant increase up to 7 months after | No change found |
| Mader et al. [28] | 2011 | 7 | Astronauts | about 6 months | Eyes and optic nerve (SANS) | 7 astronauts had eye findings after about 6 months in space (disc edema in 5, globe flattening in 5, choroidal folds in 5); a questionnaire of about 300 astronauts reported worse near or distance vision in about 29% after short and 60% after long missions | Partly |
| Kramer et al. [29] | 2012 | 27 | Astronauts | mixed | Eyes and optic nerve (SANS) | Of 27 astronauts, 7 (26%) had flattening of the back of the eye globe, 4 (15%) optic-nerve protrusion, 3 (11%) a dented pituitary | Not checked |
| Rosenberg et al. [27] | 2021 | 12 | Astronauts | long-duration | Eyes and optic nerve (SANS) | 4 of 12 astronauts met the SANS criteria; they had larger flight-related increases in venous sinus volume than the other 8 | Not checked |
| Brunstetter et al. [30] | 2025 | 16 | Astronauts | about 6 months | Eyes and optic nerve (SANS) | SANS or no-SANS on a first ISS mission predicted the same on the second mission: sensitivity 85.7%, specificity 100% | No change found |
| Carter et al. [31] | 2026 | 7 | Astronauts | about 6 months | Eyes and optic nerve (SANS) | A second 6-month mission did not raise optic-disc swelling or ventricle growth compared with the first | No change found |
| Garrett-Bakelman et al. [39] | 2019 | 1 | Astronauts | about 1 year | Eyes and optic nerve (SANS); Thinking tests | After 340 days, choroidal and retinal thickness rose in the flight twin, whose choroidal folds were already present before the mission | Not fully |
| Demertzi et al. [16] | 2016 | 1 | Cosmonauts | about 6 months | Brain activity and wiring | Motor-cortex to cerebellum connectivity and the default mode network differed after 6 months; supplementary motor area activity changed in a motor-imagery task | Not checked |
| Pechenkova et al. [14] | 2019 | 11 | Cosmonauts | about 6 months | Brain activity and wiring | No change in activation after flight, but connectivity of sensorimotor, vestibular and visual areas shifted | Not checked |
| Jillings et al. [15] | 2023 | 13 | Cosmonauts | long-duration | Brain activity and wiring | Connectivity fell in the posterior cingulate and thalamus and rose in the right angular gyrus, and stayed changed 8 months later; insula connectivity dropped but reversed | Partly |
| Salazar et al. [17] | 2023 | 15 | Astronauts | about 6 months | Brain activity and wiring; Thinking tests | Brain activity during a spatial working-memory task did not change, but connectivity of the visual areas fell | Not checked |
| Hupfeld et al. [18] | 2022 | 15 | Astronauts | about 6 months | Brain activity and wiring | Brain response to vestibular (balance-organ) stimulation changed after flight and recovered by 3 months | Yes |
| Tays et al. [19] | 2025 | 13 | Astronauts | about 6 months | Brain activity and wiring | Brain activity during a visuomotor task rose after flight and took up to 90 days to return to preflight | Yes |
| Tays et al. [20] | 2025 | 15 | Astronauts | about 6 months | Brain activity and wiring | Before flight, how separate the sensory brain networks were predicted balance after landing | Not checked |
| Bubeev et al. [37] | 2024 | 8 | Cosmonauts | in-flight training session | Brain activity and wiring | The P300 brain wave could be measured during manual docking training in space; its size was largest at medium difficulty | Not checked |
| Dev et al. [32] | 2024 | 25 | Astronauts | about 6 months | Thinking tests | In flight, processing speed, visual working memory and sustained attention were slowed early in the mission; risk-taking fell; no systematic decline over 6 months | Yes |
| Tays et al. [33] | 2021 | 15 | Astronauts | about 6 months | Thinking tests | Thinking and dual-task tests were maintained in flight and after landing; balance and mobility fell after landing and recovered within 30 days | Yes |
| Clement et al. [34] | 2023 | 28 | Astronauts | about 6 months | Thinking tests | Reaction time and time perception of people with balance-organ damage matched astronauts in flight | Not checked |
| Kuldavletova et al. [35] | 2023 | 10 | Astronauts | long-duration | Thinking tests | Reaction time got slower in flight and time intervals were under-produced while counting aloud | Not checked |
| Navarro et al. [36] | 2023 | 10 | Astronauts | about 6 to 8 months | Thinking tests | Time perception shifted in flight: one minute felt longer and hours felt shorter, while days since docking or spacewalk were judged accurately | Not checked |
| Manzey et al. [38] | 1998 | 1 | Cosmonauts | longer than 1 year | Thinking tests | One cosmonaut tested 29 times during 438 days on Mir: no impairment of basic thinking functions in flight; mood, tracking and time-sharing were worse in the first 3 weeks in space and first 2 weeks after landing, then back to baseline; no lasting deficit at 6 months | Yes |
| Jones et al. [40] | 2024 | 4 | Commercial | short under 30 days | Thinking tests | Four civilians flew 3 days: performance was largely unaffected; slower on four of ten tests in flight; post-flight the same as preflight except one test | Yes |
| Houerbi et al. [41] | 2024 | 4 | Commercial | short under 30 days | Blood markers of brain injury | Blood proteins linked to the brain changed within days of a 3-day flight; most vesicle proteins recovered within 6 months but 73% of plasma proteins were still off | Partly |
Source: IQ Metrics dataset from the papers listed (CSV below)
13 How we built the dataset
- 01
Find every study
Searches of Europe PMC and PubMed for MRI, eye and thinking-test studies of people who flew in space, plus the reference lists of a 2024 systematic review [42].
- 02
Read the paper, not the press release
Every number was read from the paper’s own text or tables; where only the abstract was open, the table says so.
- 03
One row per study and measure
59 rows for 41 studies, sorted into 9 kinds of measure, with mission length, people, the main number and whether a later check found it gone.
- 04
Never add up people
The same astronauts take part in many studies, so we report each study’s own count, never a total.
- 05
NASA's own numbers for selection
Applicants and candidates from NASA releases and history pages (public domain).
Read every number with these in mind
- The studies are small (a median of 13 people) and some use the same astronauts.
- Scans are taken 2 to 10 days after landing, so part of what they show is the brain readjusting to gravity.
- Grey-matter changes partly reflect the brain moving and fluid shifting, not tissue being lost or gained.
- Long missions of a year or more have been studied in only a handful of people.
- This page reports what the studies measured. It is not medical advice.
Sources
- New England Journal of Medicine. Roberts DR, Albrecht MH, Collins HR, Asemani D, Chatterjee AR, Spampinato MV, Zhu X, Chimowitz MI, Antonucci MU. Effects of Spaceflight on Astronaut Brain Structure as Indicated on MRI. N Engl J Med 2017;377(18):1746-1753. 2017. doi.org/10.1056/NEJMoa1705129Facts cited
- Radiology. Kramer LA, Hasan KM, Stenger MB, Sargsyan A, Laurie SS, Otto C, Ploutz-Snyder RJ, Marshall-Goebel K, Riascos RF, Macias BR. Intracranial Effects of Microgravity: A Prospective Longitudinal MRI Study. Radiology 2020;295(3):640-648. 2020. doi.org/10.1148/radiol.2020191413Facts cited
- PNAS. Van Ombergen A, Jillings S, Jeurissen B, Tomilovskaya E, et al. Brain ventricular volume changes induced by long-duration spaceflight. Proc Natl Acad Sci U S A 2019;116(21):10531-10536. 2019. doi.org/10.1073/pnas.1820354116Facts cited
- Aging Brain (Elsevier). Roberts DR, Inglesby DC, Brown TR, et al. Longitudinal change in ventricular volume is accelerated in astronauts undergoing long-duration spaceflight. Aging Brain 2021;1:100017. 2021. doi.org/10.1016/j.nbas.2021.100017Facts cited
- Cerebral Cortex Communications (OUP). Hupfeld KE, McGregor HR, Lee JK, Beltran N, et al. The Impact of 6 and 12 Months in Space on Human Brain Structure and Intracranial Fluid Shifts. Cereb Cortex Commun 2020;1(1):tgaa023. 2020. doi.org/10.1093/texcom/tgaa023Facts cited
- Scientific Reports. McGregor HR, Hupfeld KE, Pasternak O, et al. Impacts of spaceflight experience on human brain structure. Sci Rep 2023;13:7878. 2023. doi.org/10.1038/s41598-023-33331-8Facts cited
- npj Microgravity. McGregor HR, Hupfeld KE, Pasternak O, et al. Crewmember demographic factors and their association with brain and ocular changes following spaceflight. NPJ Microgravity 2025;11:59 (accepted 4 Jul 2025). 2025. doi.org/10.1038/s41526-025-00505-9Facts cited
- PNAS. Barisano G, Sepehrband F, Collins HR, Jillings S, Jeurissen B, Taylor JA, et al. The effect of prolonged spaceflight on cerebrospinal fluid and perivascular spaces of astronauts and cosmonauts. Proc Natl Acad Sci U S A 2022;119(17):e2120439119. 2022. doi.org/10.1073/pnas.2120439119Facts cited
- Scientific Reports. Hupfeld KE, Richmond SB, McGregor HR, et al. Longitudinal MRI-visible perivascular space (PVS) changes with long-duration spaceflight. Sci Rep 2022;12:7238. 2022. doi.org/10.1038/s41598-022-11593-yFacts cited
- Science Advances. Jillings S, Van Ombergen A, Tomilovskaya E, et al. Macro- and microstructural changes in cosmonauts' brains after long-duration spaceflight. Sci Adv 2020;6(36):eaaz9488. 2020. doi.org/10.1126/sciadv.aaz9488Facts cited
- npj Microgravity. Koppelmans V, Bloomberg JJ, Mulavara AP, Seidler RD. Brain structural plasticity with spaceflight. npj Microgravity 2016;2:2. 2016. doi.org/10.1038/s41526-016-0001-9Facts cited
- JAMA Neurology. Lee JK, Koppelmans V, Riascos RF, Hasan KM, Pasternak O, Mulavara AP, Bloomberg JJ, Seidler RD. Spaceflight-Associated Brain White Matter Microstructural Changes and Intracranial Fluid Redistribution. JAMA Neurol 2019;76(4):412-419. 2019. doi.org/10.1001/jamaneurol.2018.4882Facts cited
- Frontiers in Neural Circuits. Doroshin A, Jillings S, Jeurissen B, Tomilovskaya E, et al. Brain Connectometry Changes in Space Travelers After Long-Duration Spaceflight. Front Neural Circuits 2022;16:815838. 2022. doi.org/10.3389/fncir.2022.815838Facts cited
- Frontiers in Physiology. Pechenkova E, Nosikova I, Rumshiskaya A, et al. Alterations of Functional Brain Connectivity After Long-Duration Spaceflight as Revealed by fMRI. Front Physiol 2019;10:761. 2019. doi.org/10.3389/fphys.2019.00761Facts cited
- Communications Biology. Jillings S, Pechenkova E, Tomilovskaya E, et al. Prolonged microgravity induces reversible and persistent changes on human cerebral connectivity. Commun Biol 2023;6:46. 2023. doi.org/10.1038/s42003-022-04382-wFacts cited
- Brain Structure and Function. Demertzi A, Van Ombergen A, Tomilovskaya E, et al. Cortical reorganization in an astronaut's brain after long-duration spaceflight. Brain Struct Funct 2016;221:2873-2876. 2016. doi.org/10.1007/s00429-015-1054-3Facts cited
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Version history
- 2026.112 November 2026First release.
Leon Falkner, Data & Research Analyst. Leon owns the arithmetic on IQ Metrics: the percentile tables, the score converter and the figures in everyone else's drafts. On the research desk Leon pulls the data, builds each index and writes the method. More about Leon.
Questions
What happens to the brain in space?
Body fluids shift toward the head, so the brain sits a little higher in the skull and its fluid-filled ventricles grow, by about 12% to 24% over a 6-month mission. Many astronauts also get swelling at the back of the eye.
Does space damage the brain?
The studies show changes, not proven damage. The fluid spaces were still about 6% larger 7 months after landing, and thinking tests showed no lasting decline in groups of astronauts.
Do astronauts get dumber in space?
No sign of it in group studies. Astronauts were slightly slower early in a 6-month mission and back to normal after landing. No study has used an IQ test before and after flight.
How long does the brain take to recover after space?
Most of the upward shift reverses within 6 months. The ventricles were still about 6% larger after 7 months, and one study suggests about 3 years between flights for them to recover.
How hard is it to become an astronaut?
NASA chose 10 candidates from more than 8,000 applicants in 2025, about 1 in 800. In 2017 it was 12 from more than 18,300.
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You may reuse everything on this page under CC BY 4.0: in articles, reports, lessons and posts. The one condition is credit to IQ Metrics with a link to this page.
Cite this study
Version 2026.11. Citing the version lets readers find the exact numbers.
Archived copy with a DOI: 10.5281/zenodo.23909534 (report PDF and data on Zenodo).
Falkner, L. (2026). What happens to the brain in space? Every astronaut brain study (Version 2026.11) [Data set]. IQ Metrics Research. https://iqmetrics.org/research/what-happens-to-the-brain-in-space/ (DOI: 10.5281/zenodo.23909534)
Falkner, Leon. "What happens to the brain in space? Every astronaut brain study." IQ Metrics Research, 2 Nov. 2026, iqmetrics.org/research/what-happens-to-the-brain-in-space/. DOI: 10.5281/zenodo.23909534.
Falkner, Leon. "What happens to the brain in space? Every astronaut brain study." IQ Metrics Research. November 2, 2026. https://iqmetrics.org/research/what-happens-to-the-brain-in-space/. DOI: 10.5281/zenodo.23909534.
@misc{iqmetrics2026whathappenstothebraininspace, author = {Falkner, Leon}, title = {What happens to the brain in space? Every astronaut brain study}, institution = {IQ Metrics}, year = {2026}, version = {2026.11}, doi = {10.5281/zenodo.23909534}, url = {https://iqmetrics.org/research/what-happens-to-the-brain-in-space/} }
Source: Leon Falkner, "What happens to the brain in space? Every astronaut brain study." IQ Metrics Research, version 2026.11, https://iqmetrics.org/research/what-happens-to-the-brain-in-space/ (DOI 10.5281/zenodo.23909534)
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Get the data
One row per study and measure (59 rows, 41 studies): the paper, agency, crew, people who flew, controls, mission length, what was measured, the finding, its direction and size, follow-up and whether the change was gone, and where in the paper each number is.
| Column | What it holds |
|---|---|
study_id, year, journal, doi, source_url | The paper |
agency, crew, n_flyers, n_controls, control_type | Who was studied (people often appear in several studies) |
mission_class, days_mean, days_min, days_max | How long they were in space |
measure_group, finding, direction, effect, effect_unit | What was measured and what changed |
followup_months, back_to_normal | The latest check after landing and whether the change was gone (yes / partly / no / not tested) |
where_in_paper | The table, figure or section of each number |
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IQ Metrics Research collected 41 peer-reviewed studies (1998-2026) of the brains and thinking of astronauts, cosmonauts and space tourists, 59 rows by measure. After about 6 months in space the ventricles grew 11.6% (cosmonauts) to 24% (NASA, right lateral) and were still 6.4% larger 7 months after landing. After a year in space the top of the brain sat 2.52 mm higher. 21 of 37 NASA astronauts developed eye changes (SANS). Thinking tests showed a small early slowing and no lasting decline. NASA's 2025 class: 10 from more than 8,000 applicants. Source: IQ Metrics Research, https://iqmetrics.org/research/what-happens-to-the-brain-in-space/
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Quotes you can use
Attributable as written, with the name and title. For a different angle or a quote on a specific figure, ask through the contact page.
Space changes where the brain sits and how much fluid surrounds it. What the studies have not found is a lasting drop in how well astronauts think.
Leon Falkner, Data & Research Analyst, IQ Metrics ResearchSeven months after landing, the fluid spaces in a cosmonaut’s brain are only about half way back. That matters for a three-year trip to Mars.
Leon Falkner, Data & Research Analyst, IQ Metrics ResearchAlmost everything we know about the brain in space comes from a few dozen people, and many of them appear in several studies.
Leon Falkner, Data & Research Analyst, IQ Metrics Research
Files
- CSV of every study and measure, with people, mission length, finding, recovery and source (CC BY 4.0)
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Terms, contact and corrections
Credit: “IQ Metrics Research, What Happens to the Brain in Space? (2026)” with a link to this page. On air or in print, “IQ Metrics” and the page address are enough.
What it covers: peer-reviewed studies of the brain, eyes and thinking of people who flew in space, 1998-2026, and NASA’s published applicant counts.
Contact: the research team, through the contact page. Corrections are made on this page with a dated note in the version history.
