Behavioral Health and Performance: An Overview
This overview of the behavioral health and performance chapters provides a perspective on the challenges to behavioral health and performance posed by spaceflight and the lessons learned from the history of terrestrial and spaceflight expeditions, as well as the key role of assessing cognitive functions in spaceflight, ensuring adequate sleep and circadian entrainment in spaceflight, and maintaining a system to manage behavioral health in prolonged spaceflight.
Exploration of space and ultimately living in spacecraft and on celestial bodies other than Earth are logical extensions in the human story. Modern humans (Homo sapiens sapiens), the only surviving species of the genus Homo, emerged approximately 50–80,000 years ago with neurobehavioral capability and cognitive traits that include abstract thinking, planning, and development of technologies, among other skills. Since first appearing, humans have migrated over more than 80% of the total land surface of Earth. Thus, from inception modern humans have been exploring and developing technologies to go further. Space is the logical next step. In the past century, we have focused on exploring space beyond the gravitational hold of Earth and transiting to celestial bodies visible in the night sky. This exploratory goal and effort is evident in the cooperation of countries in the mutual desire to explore space and in the operation and maintenance of the International Space Station (ISS), which include the United States, Russia, Canada, and Brazil and European Space Agency members (Belgium, Denmark, France, Germany, Italy, the Netherlands, Norway, Spain, Sweden, Switzerland, the United Kingdom), as well as in the independent efforts of a growing number of other countries (e.g., China National Space Administration, Indian Space Research Organization).
In the past half century, since the first rudimentary space station was created in 1969 by the linking of two Russian Soyuz vehicles in space, a growing number of humans have been spending an increasing amount of time in space on the International Space Station, which serves as both a research platform and a prelude to remaining for longer periods of time in space – which is the information needed for estimating the effects of transiting to and living on other celestial bodies. As a research platform, ISS makes possible a wide range of science, including that relevant to human behavioral health and performance, which is the focus of this overview.
Spaceflight to other celestial bodies will require living confined for prolonged periods while in microgravity or partial gravity (relative to Earth’s 1g force); being away from family, friends, and Earthly activities; time delays limiting communications and both operational and personal support; and exposure to both expected and unexpected potentially lethal conditions (e.g., radiation, toxic materials, extreme temperatures, loss of artificial atmosphere or pressurization, etc.). All of these factors and more are often referred to as the stressors of human space exploration, because they pose significant challenges to human behavioral health and performance in space. These challenges also encompass the adverse effects on the brain and behavior associated with prolonged spaceflight and habitation on other celestial bodies. They broadly include the following four domains: (1) neurobehavioral deficits in the ability to engage, comprehend, and perform tasks at a consistently high level due to biological challenges in space (e.g., deficits due to inadequate sleep, poor circadian entrainment, visual impairment); (2) deficits in specific cognitive functions subserved by particular brain areas, neural pathways, or cortical networks adversely affected by environmental conditions (e.g., deficits due to excessive carbon dioxide, hypoxia); (3) alterations of psychological states related to mental and emotional processes (e.g., disorders of depression, anxiety, and psychosis); and (4) psychosocial dysfunction among crewmembers and/or with mission control, which includes loss of crew coordination and team cohesion (e.g., due to interpersonal conflicts, scapegoating, failure to follow procedures).
As detailed by Stuster, in his article on “Behavioral Challenges of Space Exploration,” the history of nineteenth- and twentieth-century exploration – especially of Earth’s polar regions – contains numerous examples of serious psychological problems in some crewmembers. It is presumed these responses were due to the harsh conditions and to the isolation, confinement, and other stressors of expedition life. However, it is not known to what extent individual differences in biological vulnerability to these factors (or to other precipitating events) have been the actual reason for the behavioral health and performance responses in some expedition members, but not in others. Recent scientific evidence suggests there are large phenotypic differences in vulnerability to behavioral stressors. For example, there is a considerable range in the phenotypic vulnerability to the effects of sleep deprivation on cognitive performance (Basner et al. 2013a) and metabolic responses (Spaeth et al. 2015). Similar interindividual differences related to differential vulnerability to the effects of prolonged confinement and limited communications with Earth were found in a high-fidelity 17-month simulated mission to Mars (Basner et al. 2013b, 2014). There is a critical need to identify biomarkers for differential vulnerability to the varied neurobehavioral effects of spaceflight, in order to optimize crew selection, tailor countermeasure needs, and ensure personalized medicine for behavioral health and performance in space.
As noted by Sipes et al. in their article on the “Managing Behavioral Health in Space,” due to the high frequency and severity of risk to mission success posed by deficits in crew behavioral health and performance, NASA ranks the risks to behavioral health and performance during prolonged habitation in space second only to the risks of space radiation exposure, as a potential impediment to a successful exploration class mission. As a result NASA has a rather comprehensive aerospace medicine and aerospace psychology program to positively influence the mental well-being of astronauts, cosmonauts, and their family members.
In evaluating the literature on the psychosocial aspects of groups living and working in extreme environments, Kanas concludes in his article on “Crewmember Interactions in Space” it is important for space crews to have good interpersonal relationships and open channels of communication. Mission characteristics, individual differences, and issues related to culture can all affect the interactions of crewmembers. Understanding these issues, and developing ways to select and train crewmembers to optimize crew relationships, can facilitate mission success.
However, good crew communication and crew cohesion alone are not enough to enhance the likelihood of a successful mission if one or more crewmembers experience serious neurobehavioral deficits and/or dysfunctions in one of more cognitive functions due to a variety of conditions in spaceflight, some of which may not yet have been identified as causal of cognitive deficits. As pointed out by Strangman et al. in their article on the “Cognitive Performance in Space,” complaints of cognitive deficits (especially problems concentrating, remembering, and cognitive slowing) have been common in spaceflight for decades. These reports have varied greatly among astronauts and within missions. Thus there are both high interindividual and within-individual variability in cognitive performance during spaceflight. It is not yet understood why certain astronauts are more cognitively sensitive than others to the spaceflight environment. This variability may be related to differential experiences of chronic stress, differential vulnerabilities to sleep restriction, cumulative exposure to spaceflight conditions, as well as genetic makeup, neurobiological vulnerability to occult conditions in space, or other factors. Improved cognitive assessments in spaceflight will provide much-needed information on the cognitive risks of long-duration missions.
Two ubiquitous and interrelated biological challenges to behavioral health, neurobehavioral functions, and cognitive performance capability in spaceflight involve maintaining the ability of astronauts to obtain daily adequate sleep duration and good sleep quality. This means that the 24-h (circadian) rotation of Earth on its axis, which is instantiated in the behavioral biology of humans, must be maintained in the artificial confines of spaceflight and habitation on distant planets, even in the present of a planet’s axial rotation that is not 24 h (e.g., Mars has a 24.65-h day). There is extensive scientific evidence to suggest that inadequate daily sleep duration, frequent poor-quality sleep, and chronic problems maintaining circadian sleep-wake cycles will have potentially catastrophic effects on crew physical and behavioral health, performance, and safety during space missions. As observed by Barger et al. in their article on “Sleep and Circadian Effects of Space,” countermeasures are needed to ensure adequate sleep quantity and quality of crewmembers and to promote circadian alignment during long-duration missions. These include biologically optimized work-rest scheduling, strategically timed exposure to specific wavelengths and intensities of light, and behavioral strategies to ensure adequate sleep quantity and quality. As described by Klerman in the article on “Modeling and Entraining Human Capability in Space,” mathematical models of human circadian rhythms, sleep, performance, and alertness have been developed, and they can be used to predict how individuals will function on different schedules, to suggest strategies to improve performance and the ability to entrain circadian rhythms, and to optimize the use of countermeasures such as light, naps, and pharmaceuticals in prolonged space missions.
As humans prepare for prolonged exploration of space and habitation of celestial bodies, their successes will depend heavily on the behavioral health and performance capabilities of the crew. Automation, robotics, and other technologies can greatly facilitate the chance of success, but the human brain and behaviors it regulates will be the ultimate determinant of the outcome.
- Basner M, Dinges DF, Mollicone DJ, Ecker AJ, Jones CW, Hyder E, Di Antonio A, Savelev I, Kan K, Goel N, Morukov BV, Sutton JP (2013b) Mars 520-d mission simulation reveals protracted crew hypokinesis and alterations of sleep duration and timing. Proc Natl Acad Sci U S A 110(7):2635–2640CrossRefGoogle Scholar
- Basner M, Dinges DF, Mollicone DJ, Savelev I, Ecker AJ, Di Antonio A, Jones CW, Hyder E, Kan K, Morukov BV, Sutton JP (2014) Psychological and behavioral changes during confinement in a 520-day simulated interplanetary mission to Mars. PLoS One 9(3):e93298. https://doi.org/10.1371/journal.pone.0093298CrossRefGoogle Scholar
- Spaeth AM, Dinges DF, Goel N (2015) Phenotypic vulnerability of energy balance responses to sleep loss in healthy adults. Scientific Reports, Oct. 8, Article No.: 14920. http://www.sciencedirect.com/science/article/pii/S0094576514002793