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Astronauts on current and future spaceflight missions are required to execute complex tasks in which even minor errors could have devastating consequences. Intact cognitive functioning is critical to maintain exceptional performance standards during long duration spaceflight missions. However, astronauts are exposed to spaceflight environmental stressors that include spaceflight hazards (i.e., radiation, altered gravity, isolation and confinement, hostile/closed environment, and distance from Earth) as well as operational challenges (e.g., work overload, circadian shifts, communication delays) that could compromise cognitive functioning (Slack et al., 2016). Some of these challenges are experienced by astronauts living and working on the International Space Station (ISS), yet the extent to which cognitive performance decrements are observed on ISS missions remains critically under-characterized.

Anecdotal and self-report evidence suggest some astronauts experience subjective cognitive difficulties inflight (Stuster, 2010; Stuster, 2016; Schroeder and Tuttle, 1992; Clément et al., 2020), particularly for tasks requiring sustained attention and speed of processing. However, objective assessments of cognitive performance in spaceflight have yielded mixed findings (For review see Thoolen and Strangman (2023)). Early studies assessing dual tasking performance in short duration shuttle missions suggest that attention may be adversely impacted during tasks that include a primary sensorimotor component (Heuer et al., 2003; Manzey et al., 1995; Manzey et al., 2000). More recent studies examining cognitive performance during 6-month ISS missions have largely focused on specific cognitive domains. For example, Jones et al. (2022) recently reported that astronauts who obtained 5 h or less of sleep on the ISS performed worse on a task of sustained attention. Relative to pre-flight, slowed reaction time on a task of spatial working memory post-flight but not during flight (Tays et al., 2021), decrements in visuospatial line orientation inflight and early post-flight (Takács et al., 2021), and increased error on a dual tasking paradigm on landing day (Moore et al., 2019) have been reported. The post-flight decrements observed in these studies returned to pre-flight levels over 30 days follow up. In contrast, no differences were reported in spatial working memory accuracy, processing speed, cognitive-dual tasking, and visual memory (Burles and Iaria, 2023; Moore et al., 2019; Tays et al., 2021). This body of literature is limited by small samples, lack of measurement standardization across studies, limited sensitivity of measures to detect change in high performing populations, and inconsistent timepoints within mission (Strangman et al., 2014). Further, the scope of cognitive domains assessed is restricted and there is an overall paucity of data documenting other cognitive functions that may impact mission relevant tasks, such as memory, executive functions, and emotional processing. Nevertheless, current evidence suggests at most mild and reversible decrements in aspects of cognition among astronaut crew on ISS missions of 6-month duration or shorter.

Only one published study to date has comprehensively assessed a wide range of cognitive domains across multiple mission phases in spaceflight. The well-known NASA Twin study (Garrett-Bakelman et al., 2019) conducted cognitive testing using the Cognition Battery (Basner et al., 2015) in a pair of monozygotic twins, one of which spent approximately 1 year (340 days) on the ISS while the other remained on Earth. Early inflight improvements were documented in speed and accuracy, with the exception of accuracy decrements in specific domains of visual memory and abstract reasoning (>1 standard deviation [SD] decline). Relative to early flight, late flight performance was slower in emotion recognition (>1SD) and less accurate in abstract reasoning (>2 SD). However, the most notable decrements were observed in the post-flight mission phase across most cognitive domains that persisted up to 6 months. Though a single case study, findings underscore the relevance of assessing a breadth of cognitive domains in spaceflight, support previous studies indicating that cognitive performance may be differentially impacted at different mission phases, and suggest that longer duration missions may induce more persistent decrements.

Terrestrial analogs that simulate spaceflight conditions offer a unique opportunity to study singular or combined spaceflight hazards and stressors on relevant behavioral health and performance outcomes. Group level changes in cognitive performance were not present in several long duration European, Russian, and Antarctic analog missions (Lorenz et al., 1996; Gemignani et al., 2014; Mairesse et al., 2019; Connaboy et al., 2020). However, a subset of individuals in these settings appear to be more vulnerable to decrements in aspects of attention, memory, or visuospatial abilities, including those who report depressive symptoms (Premkumar et al., 2013), heightened stress and sleep loss (Basner et al., 2014), and greater hippocampal volume loss (Stahn et al., 2019). Indeed, sleep restriction protocols implemented in one- and 2-week isolation and confinement spaceflight analogs were associated with worse emotion recognition, slower and less accurate sustained attention, and slower cognitive and psychomotor processing speed (Nasrini et al., 2020). Other studies also have examined the effects of altered gravity on cognition. Parabolic flight studies assessing impacts of acute gravitational alterations have documented decrements on tasks of spatial cognition (Stahn et al., 2020) and attention (Friedl-Werner et al., 2021). Head Down Bed Rest (HDBR) studies, designed to simulate cephalic fluid shift in microgravity, report that prolonged HDBR can induce early but mild reductions in overall cognitive speed that remain consistent for the duration of the protocol (Basner et al., 2021a) and more specific decrements on tasks of executive functioning (Yuan et al., 2016), emotional processing (Basner et al., 2021a; Brauns et al., 2019; Benvenuti et al., 2013; Liu et al., 2012), and aspects of memory (Chen et al., 2013). Decrements resolve soon after returning to normal daily activities and were only exacerbated by a combined HDBR and CO₂ protocol in isolated tasks of executive function and sustained attention (Basner et al., 2021b; Lee et al., 2019; Mahadevan et al., 2021). Thus, analog studies have identified mild, possibly reversible, decrements in cognitive performance across several domains in the context of spaceflight stressors. Even among those that did not report significant group level differences, observed individual variability in performance suggests that some individuals are more at risk for cognitive decrements than others.

Taken together, the extant literature documenting cognitive performance in spaceflight or spaceflight analogs suggests possible mild decrements in some, but not necessarily all, cognitive domains and that these decrements may be singularly or synergistically influenced by multiple spaceflight hazards (e.g., altered gravity) and stressors (e.g., sleep restriction). Given the dynamic nature of spaceflight missions and thus the potential for hazards and stressors to interact in varying degrees within a mission, it is also possible that there are specific mission phases in which performance is more vulnerable to decrements. However, we were unable to locate a published study that has described the neuropsychological profile expected in low earth orbit spaceflight by systematically assessing cognitive performance across a wide range of cognitive domains in a cohort of astronauts aboard the ISS for 6-month missions.

The primary aims of the current study were to 1) provide a descriptive summary of performance across several cognitive domains in a sample of professional astronauts on 6-month ISS missions, 2) characterize cognitive performance over time and between distinct mission phases of a 6-month ISS mission, and 3) examine the prevalence of low scores across subtests. While we generally expected stable cognitive performance across time, we predicted that performance would be most vulnerable during mission phases that require greater adaptation to and from spaceflight conditions. Further, processing speed, attention, and working memory are cognitive domains which are more susceptible to state-like alterations due to internal or external distractions (Eysenck and Calvo, 1992; Robert and Hockey, 1997). Thus, we hypothesized that 1) there would be mild decrements in early flight and early post-flight mission phases relative to pre-flight; and 2) the subtests with the greatest frequency of low scores would be those assessing processing speed, attention, and working memory. Finally, given previous studies identifying individual differences predicting variability in cognitive performance, we also explored the relationship between self-reported sleep and ratings of alertness.

Data were downloaded, processed, visualized, and inspected for quality. Data from four subtests were excluded from data analysis, not necessarily from the same individual: one was excluded due to technical difficulties that interfered with task performance, two were excluded due to suspected non-adherence (i.e., pattern of accuracy and speed outliers indicative of rapid responding rapid and/or careless responding and elevated false positives; (Basner et al., 2015)), and one was excluded due to a participant comment indicating confusion with subtest instructions. Table 1 displays raw baseline (i.e., pre-flight) scores used to generate z-scores for the present analysis and can be used as a preliminary normative database for future studies. Descriptive information for each subtest’s z-scores by mission phase is presented in Table 2.

This investigation characterized performance across a wide breadth of cognitive domains in a sample of 25 astronauts on 6-month ISS missions. We were unable to locate any published studies with a more comprehensive or larger dataset on a sample of astronauts; thus, we believe this study makes a substantial contribution in characterizing astronaut cognitive performance in spaceflight. We have reported pre-flight baseline descriptive information characterizing cognitive performance across all subtests that can be utilized as a preliminary normative database for future research. As a group, astronaut crew demonstrated generally stable performance on summary measures of cognition and only mild changes in isolated cognitive domains during specific mission phases. Specifically, slowed performance was observed early in flight on tasks of processing speed (i.e., DSST), visual working memory (i.e., F2B), and sustained attention (i.e., PVT); slowed processing speed and working memory persisted into post-flight. Risk taking propensity also reduced after the early flight mission phases. A total of 11.8% of all flight and post-flight scores were classified as low, such that they fell at or below 1.5 standard deviations below the sample’s pre-flight baseline mean. Finally, exploratory analysis found no consistent relationships between cognitive performance and either self-reported amount of sleep or ratings of alertness. This study makes three important contributions which are discussed next.

First, we report no systematic decline in cognitive performance during 6-month low earth orbit missions among the largest sample of professional astronauts published to date. This is in contrast to some of the previous research that observed declines across several cognitive domains during flight and post-flight mission phases (Garrett-Bakelman et al., 2019; Takács et al., 2021). Our results do not necessarily contradict these findings as we also observed interindividual variability in our sample and it is possible that longer duration missions elicit greater decrements at later mission phases. However, we did not find support for group level impacts of spaceflight conditions on cognitive performance in low earth orbit.

Next, by using a comprehensive assessment of cognitive functions we identified cognitive domains that were more variable across phases of a 6-month low earth orbit missions. This suggests that these cognitive domains are more vulnerable to spaceflight conditions than other domains. Specifically, we observed early flight slowed performance, but stable accuracy, on tasks of processing speed and visual working memory that persisted through the duration of the mission. Visual working memory speed did not return to pre-flight levels at 30 days post mission. Slower performance on the PVT was observed during early flight only. Notably, these decrements were present despite generally preserved, or even improved, sensorimotor functioning. These findings are consistent with astronaut self-report of “brain fog” (Clément et al., 2020; Stuster, 2010; Stuster, 2016), the NASA Twin Study (Garrett-Bakelman et al., 2019), and analog studies simulating prolonged microgravity (Basner et al., 2021a; Basner et al., 2021b; Liu et al., 2012; Lipnicki and Gunga, 2009) and sleep restriction (Wang et al., 2014). This is also consistent with documented pre to post mission alterations in brain structure and function (Roy-O’Reilly et al., 2021; Doroshin et al., 2022; Jillings et al., 2023) that can contribute to cognitive inefficiency. Our results also revealed decreases in the BART risk taking score after the early flight mission phase, suggesting that astronauts were less likely to take risks in late mission and post mission phases. Greater comfort with risk taking at early flight may reflect the novel and inherently hazardous nature of operational activities that require crew to accept risk in order to complete. Risk taking is relatively understudied in spaceflight despite the hazardous environment, though others have reported increases in flight (Garrett-Bakelman et al., 2019), no changes during simulated prolonged microgravity (Basner et al., 2021a; Basner et al., 2021b), and decreases during social isolation (Erskine-Shaw et al., 2017; Zivi et al., 2023) and fatigue (Hisler and Krizan, 2019). This finding warrants further study as the ability to modulate risk taking propensity across the mission may be an adaptive skill that enables the astronaut to appropriately approach mission demands. Finally, we observed no decrements in concept formation, abstract reasoning, or visuospatial learning and memory, though other studies indicate there may be individual differences in vulnerability to decrements in these domains (Premkumar et al., 2013; Garrett-Bakelman et al., 2019). Indeed, frontal and hippocampal structures that support these functions are sensitive to radiation exposure (Desai et al., 2022), stress (Mandrick et al., 2016; Wingenfeld and Wolf, 2014), isolation and confinement (Stahn et al., 2019), and microgravity (Koppelmans et al., 2016; Lee et al., 2021; Li et al., 2015). Thus, it is possible that longer duration missions with greater exposure to spaceflight hazards or individual vulnerabilities to stressors will exacerbate decrements in future exploration missions.

Finally, we present the first published professional astronaut preliminary normative dataset for the Cognition Battery that can be used to derive standard scores to identify significant deviations from pre-flight baseline functioning. For example, despite modest group level differences in cognitive performance across most subtests, 11.8% of observations across all tasks during flight or post-flight fell at or below 1.5 standard deviations of the samples pre-flight baseline mean. The greatest number of observations below cut off were on tasks assessing working memory, processing speed, and sustained attention, which are domains vulnerable to state-like alterations related to acute changes in sleep (Jones et al., 2022; Lim and Dinges, 2010), stress (Eysenck and Calvo, 1992), workload (Ghalenoei et al., 2022), and dehydration (Wittbrodt and Millard-Stafford, 2018). Though there is no evidence of an increased frequency of low scores in this sample compared to other cognitively healthy populations (Crawford et al., 2007; Binder et al., 2009), even highly infrequent or temporary barriers to adequately engaging cognitive functions required to perform complex operational task may result in catastrophic consequences in spaceflight. This preliminary normative dataset provides operational support with the ability to identify low scores during flight, elucidate effective in mission support to enhance performance (i.e., stress reduction, timeline alterations), or inform concept-of-operations during mission critical tasks. This dataset can also be utilized in future research to compare performance against future astronauts on extended duration missions or those that venture beyond low earth orbit and include more extreme stressors.

These significant contributions underscore critical knowledge gaps that should be prioritized for future research. First, there are likely individual differences in susceptibility to spaceflight environmental stressors. The current sample size was too small to stratify our normative baseline by age. Although we did not find clear associations between cognitive performance and self-reported hours of sleep or ratings of alertness, there are several other stressors that are not accounted for in the current dataset such as workload, stress and fatigue specific to extravehicular activities, nutrition/exercise, and individual behavioral health. These may become more impactful during future space exploration missions as conditions of greater radiation exposure, extra-vehicular surface activities, and earth independent operations deplete individual cognitive reserve to unmask larger decrements. The operational consequences to observed changes in cognitive performance also remains unknown. The everyday demands required of spaceflight are more complex, dangerous, and uncertain than those of terrestrial life suggesting that current clinical thresholds to define impairment may not be appropriate. Basner et al. (2020b) reported associations between a spaceflight docking task and processing speed, sustained attention, visuospatial orientation, and abstract reasoning, suggesting that this mission critical task is vulnerable to some of the decrements we observed in this investigation. Future studies investigating the relationship between cognitive performance and other operationally activities are required to determine appropriate decrement thresholds beyond which performance is most at risk. Further development of earth independent operational supports to maintain optimal cognitive performance will further reduce the risk to individual cognitive health and performance on operational tasks.

The reported results should be interpreted in the context of some limitations. Despite applying corrections for practice effects, the reported data suggests continued improvement over time in a subset of the Cognition Battery subtests. This likely due to small sizes and key differences between our study design and that of the published corrections, including administration intervals (i.e., 10–28 days vs > 60 days) and population (i.e., university vs. operational settings). Updates to the practice corrections may be warranted now that the Cognition Battery has become more commonly used among several high performing operational environments. Cognitive performance assessed during the early flight and early post-flight stages were collected on average 28.88 (SD = 10.01) days after launch and 9 (SD = 1.85) days after landing. Thus, performance was not characterized during what may be the most acute transitional phases of a mission or during long term follow up. Nevertheless, the pre-flight data published here is the first preliminary astronaut normative dataset that can be used in future studies to derive standard scores for independent samples.

In summary, we observed no evidence for systematic widespread declines in cognitive performance suggestive of damage to the central nervous system during 6-month ISS missions. Our results revealed early mildly slowed performance in isolated tasks of processing speed, working memory, and attention that persisted to varying degrees through the mission, reduced risk taking after early flight mission phases, and stable performance on tasks of memory and executive functions. This investigation makes a substantial contribution by providing a pre-flight normative sample of professional astronauts that can be used to characterize individual or group level deviations from baseline functioning, characterizes cognitive performance under conditions of spaceflight in low earth orbit, and substantially shapes a growing body of literature towards a future that best positions humans to thrive in space.