Among the myriad challenges that will be faced by astronauts during long-duration space expeditions and extended stays on extraterrestrial “way stations” are three unique stressors: (1) prolonged exposure to solar and galactic radiation; (2) prolonged periods of exposure to microgravity; and (3) confinement in close, relatively austere quarters along with a small number of other crew members with whom the astronaut will need to live and work effectively for months (or even years) on end, with limited contact with family and friends and no possibility of direct outside human intervention.1
Accordingly, research in the next decade must include studies aimed at (1) determining the mission-specific effects of these and other relevant stressors, alone and in combination, on the astronauts’ general psychological and physical well-being and (2) development of interventions to prevent, minimize, or reverse deleterious effects during extended missions. For the first of these aims, the emphasis should be on determining the extent to which such stressors impact astronauts’ capacity to perform mission-related tasks, both as individuals and as members of a team—and thus, the extent to which such stressors constitute a risk to mission success.
From a behavioral standpoint, the most salient threats to astronaut effectiveness during long-duration missions include the following risks:
• Psychological and physiological well-being of individual astronauts might decline over time, impacting astronaut effectiveness and accomplishment of mission goals.
• Team cohesiveness and effectiveness might erode to the extent that team performance and mission success are jeopardized.
• Brain physiology and cognitive functioning of astronauts might be adversely affected either directly (e.g., by factors such as long-term radiation exposure) or indirectly (e.g., by chronically inadequate sleep) to the extent that mission performance and success are jeopardized.
Nevertheless, scientific studies aimed at identifying and quantifying the effects of such factors are sparse. This is largely because of understandable concerns about protecting the confidentiality of astronauts’ behavioral and mental health data. For example, the 2010 National Aeronautics and Space Administration (NASA) Human Research Road Map2 lists the following risks under the Behavioral Health and Performance category: risk of performance errors due to fatigue resulting from sleep loss, circadian desynchronization, extended wakefulness, and work overload; risk of performance decrements due to inadequate cooperation, coordination, communication, and
psychosocial adaptation within a team; and risk of adverse behavioral conditions and psychiatric disorders. Yet NASA’s policy has been to restrict access to psychological test material and other personal information needed to investigate how these factors affect performance, behavior, or mental health. As a result, empirical studies assessing the dynamics of these risks and their impact on mission performance and health are sparse; most of the relevant information is more anecdotal than evidence-based. Therefore, prominent among current priorities is the need to improve access to relevant data in a manner that is consistent with both the confidentiality rights of the astronauts and the scientific imperatives of NASA’s mission.
To realize the full potential of crewed space missions, it is critical that appropriately selected astronauts are provided an environment that ensures not only their physical health and well-being but also their psychological health and their continued capacity for higher-order cognitive abilities such as problem solving, situational awareness, and judgment—as well as those human qualities such as inquisitiveness, courage, and determination upon which the successful exploration of space ultimately depends.
Although recent work (e.g., using functional brain imaging techniques) has begun to reveal the physiological basis of cognitive performance, there is currently no physiological marker of “general cognitive performance capacity” or “cognitive reserve.”3 At present, the only way to determine cognitive performance capacity is to administer cognitive tests designed to assess specific aspects of cognitive ability such as learning, problem-solving, emotional lability, and so on.
Because space is a hostile and unforgiving environment, even small errors in judgment or coordination can potentially have profoundly adverse consequences. Construction, repair, and exploration in space depend upon extravehicular activities, involving elaborate preparation by astronauts. In their review, Mallis and DeRoshia list a number of documented incidents involving operational performance errors by astronauts, along with evidence of irritability, impatience, declines in performance on a reasoning task, etc., during American and Soviet space missions.4Figure 5.1 shows a photograph of an astronaut performing an extravehicular activity with his boots on the wrong feet. Although this error resulted in no damage to astronaut, suit, or vehicle, it nevertheless serves as a prosaic reminder that lapses in attention and cognitive performance can and do occur during space missions. It is not difficult to envision serious (even catastrophic) consequences of such lapses.
Cognitive functioning considerations also pertain to ground crew. As pointed out by Mallis and DeRoshia, ground control personnel provide around-the-clock coverage of critical tasks during space missions, and they can be affected in unique ways.5 For example, ground crews working on Mars Exploration Rover operations were required to adapt their work schedules to the 24.6-h Mars sol, which meant that work shifts were initiated 39 min later each day. Because they were exposed to Earth’s 24-h light/dark cycle while continuously shifting their work schedules later each Earth day, it is likely that alertness/performance deficits accrued in these individuals due to circadian desynchrony (experienced by travelers as “jet lag”). Additional research is needed to determine the effects of such schedules on ground crew performance and to devise strategies to ensure that adequate alertness and performance in these individuals can be sustained.
Several neuropsychological and cognitive assessment metrics and batteries currently exist; most were initially developed for the purpose of identifying deficits in neuropsychological functioning that reflect some underlying pathological state. Identification of such deficits or states during space missions is, of course, critical; accurate identification of depression, attention deficits, sleepiness, anxiety, etc., is needed to ensure application of appropriate countermeasures and to subsequently assess the efficacy of those countermeasures. However, the ultimate utility for NASA of cognitive performance testing lies in its potential to (1) inform the astronaut selection process and (2) provide meaningful data for detecting trends in the astronauts’ (and the ground crew’s) status during actual missions. In this context, “status” includes their capacity to perform mission-related tasks and their mood and level of psychological health/well-being at both individual and group levels. This means that cognitive tests must
be selected or developed that are not only optimally valid and reliable but also optimally sensitive to potentially subtle neuropsychological deficits caused by stressors unique to the astronauts’ environment (e.g., microgravity, exposure to radiation, isolation, monotony, and environmental pollution) and/or the ground crew’s environment (e.g., circadian desynchrony).
To the extent possible, the cognitive capacity of astronauts should be monitored using embedded measures—for instance, reaction time when working at a computer monitor or efficiency in operating a robotic arm during typical mission-related duties. The use of noninvasive performance measures could obviate the need for implementation of (at least some) dedicated assessment/testing. Any additional cognitive tests to be administered should be (1) validated against specific, mission-relevant tasks (e.g., associated with monitoring and maintenance of equipment) and/or (2) selected to reflect abilities deemed desirable for the human exploration aspects of the mission (problem solving, situational awareness, etc.).
1. Cognitive tests (including noninvasive embedded measures) that are relevant to or predictive of mission-related tasks should be identified or developed. Research could be conducted mostly in laboratories and analog environments on Earth; this research enables space missions.
2. Cognitive tests should be validated against actual mission performance. Research should be conducted in actual work environments of interest or in high-fidelity simulators or analog environments (e.g., ground control facilities or the International Space Station [ISS]).
3. Astronauts, ground crew, and other NASA personnel should be made aware of how cognitive and psychological research is increasingly critical for mission success and should be encouraged to participate in such research. Psychological and cognitive research should be prominent in the astronaut training curriculum, with
an emphasis on eliminating misconceptions, negative attitudes, and fears regarding such research. This research enables space missions.
4. NASA management should ensure that relevant data are made available for psychological and cognitive research, including previously collected (albeit de-identified) data. This is research that enables space missions. In addition, this is research that could well be completed in the near term.
5. Cognitive testing during the selection process should be aimed at determining not only the extent of an individual’s abilities within relevant cognitive domains but also the extent to which candidates are likely to retain and effectively use cognitive capacity when experiencing mounting exposure to stressors (i.e., cognitive resilience). Thus, measures of cognitive resilience should be identified or developed to facilitate longitudinal assessment of astronauts’ capacity for sustaining performance in the face of significant stressors, particularly in the context of challenging situations such as docking, EVAs, equipment failures, etc. Efforts to measure individual characteristics such as “cognitive reserve” (which may underlie various aspects of psychological and cognitive resilience) should be developed. Test development strategies in which cognitive testing is administered under challenging conditions such as sleep loss or hypoxia might be appropriate. This research, which enables space missions, could take place in ground-based laboratories.
Although new measures may be salient, it is likely to be more productive to construct or adapt cognitive test batteries for astronauts from existing tests/resources—taking advantage of previous efforts to establish validity, reliability, and norms. Resources such as the National Institutes of Health Toolbox should be used to leverage development of optimally useful cognitive testing regimens.
6. Cognitive testing and monitoring should include ground crew, who may also be subjected to unique stressors during missions (e.g., adaptation of work schedules to the martian light/dark schedule) and upon whom mission success also depends. This is research that enables space missions.
7. Behavioral scientists should be included in the initial phases of planning for future missions involving protracted flight and for studies in which extended expeditions are simulated or undertaken.
The adaptation of the individual astronaut to the novel conditions of space and increasing distance from Earth must be considered in directing research activities over the next decade. Major priorities are methods and interventions to maintain optimal psychological and behavioral functioning and to prevent or treat mental disorders that might develop in the space environment.
Current research needs and priorities to support optimal individual functioning during long-duration missions in many respects mirror recommendations made in 1998 by the NRC Committee on Space Biology and Medicine on topics to be examined.6
The first opportunity to identify candidates who are better able to withstand the rigors of space missions is during astronaut selection. Astronauts, and later exploration crews, are chosen not only for their technical skills but also for their psychological hardiness and ability to live and work with others in a confined and extreme environment. Tests that accurately determine the optimal configuration of personality traits, coping skills, and cognitive capabilities are needed to assess functioning at the time of selection, for monitoring during space missions, and to predict the likelihood that functioning will become impaired (i.e., some type of behavioral or mental disorder will develop over time in the operational environment).
Astronaut candidates have been evaluated by means of self-report personality inventories and formal psychiatric interviews to screen for subclinical and clinical disorders and family history of mental disorders, following a “select out” strategy. However, greater attention needs to be paid to the identification of less obvious subclinical
and clinical personality patterns and traits that could be exacerbated during a long-duration mission and could have deleterious effects on both individual and group performance.7 Although “select-in” strategies have been applied less frequently, they are important in identifying psychological strengths that optimize adaptive functioning in the space environment, for example, resilience in coping with significant adversity. These positive characteristics also can be assessed in different types of analog environments. Evaluation of the individual’s behavior in such settings, supplemented by the use of established psychometric instruments, may serve two purposes: (1) improved screening and selection based on possession of assets or individual strengths rather than the absence of weaknesses or deficits and (2) development of interventions defined to develop resilience under adverse field situations.
Further, selection will not be entirely effective if different nations participating in exploration missions use different selection criteria. The administration of a core battery of personality measures with norms standardized for each country could improve the selection process and provide informative data on the prediction of both positive and negative outcomes involving individuals in mixed gender and international crews.
Selection is, of course, only the first step toward ensuring positive psychological functioning. NASA has implemented stress management training and informal behavioral observation to ascertain how individuals deal with stress and interact with other team members. However, standardization of training programs and comprehensive research to evaluate the effectiveness of these programs need to be conducted. More effective training programs focused on dealing with family problems will help ensure the continued behavioral health of astronauts and their families in all phases of their involvement with NASA and beyond. Family members, both in the immediate nuclear family and in the extended family, have myriad concerns not just in coping with the absence of the astronaut but also about matters such as how and what to communicate with astronauts during long-duration missions.
Even though astronauts are psychologically healthy at the time of selection, they have reported symptoms reflecting psychological dysfunction during space missions.8,9 To the extent that these psychological problems developed in response to the rigors of the space environment (rather than indicating inadequate screening), it is likely that such problems will be exacerbated during exploration missions involving greater isolation from Earth and separation from family and significant others over increasingly extended periods of time. Table 5.1 lists several psychological symptoms that have been reported in analog settings (polar expeditions) and space missions, respectively. Such endeavors are similar in several critical ways, and as shown, there are commonalities among the symptoms produced under both conditions.
Studies of individuals in analog environments suggest that the experience of spaceflight and the novelty of the environment may also generate positive mood and behaviors, thus enhancing positive adaptation and mitigating negative mood symptoms and possible decrements in performance.10 These findings highlight the complexity of human adaptation to such environments and reinforce the need for additional studies utilizing analogs and high-fidelity simulations. Research on factors that might facilitate astronaut habituation to (and thereby partially offset the deleterious effects of) the harsh space capsule environment should be investigated in such analog environments. Examples of analog and simulation settings on Earth of relevance to human space missions include the following, as listed in Kanas and Manzey:11
• Arctic and Antarctic expeditions,
• Mountain climbing expeditions,
• Submarines and ships at sea,
• Remote sea-based oil drilling platforms,
• Underwater simulators (e.g., marine science habitats),
• Land-based simulators (e.g., hyperbaric chambers),
• Aircraft cockpit simulators, and
• Hypodynamia (bed rest) study settings.
TABLE 5.1 Psychological Symptoms Reported During Space Missions and an Analogous Setting: Polar Expeditions
|Psychological Symptoms Noted During Spaceflighta||Psychological Symptoms During Polar Expeditionsb|
|Stress-related cardiac arrhythmias||
Rheumatic aches and pains
Difficulty falling asleep
Difficulty staying asleep
Loss of slow-wave sleep
Loss of rapid eye movement sleep
Reduced accuracy and increased response time for cognitive tasks of memory, vigilance, attention, and reasoning
Easily hypnotized and susceptible to suggestion
Spontaneous fugue states (Antarctic stare)
Anger and irritability
|Interpersonal tension and conflict|
Toward group members
Toward people external to the group
aN. Kanas and D. Manzey, Space Psychology and Psychiatry, 2nd Edition, Microcosm Press, El Segundo, Calif., and Springer, Dordrecht, The Netherlands, 2008.
bL.A. Palinkas and P. Suedfeld, Psychological effects of polar expeditions, Lancet 371(9607):153-163, 2008.
The possibility of mental disorders developing in space is a significant concern. Both psychological and biological approaches are being pursued to identify vulnerability to psychological dysfunction. Based on extended experience with long-duration missions, the Russian space program has identified a psychophysiological condition termed asthenia, evident in approximately 60 percent of cosmonauts who have flown in space.12 This syndrome is characterized by symptoms of fatigue and exhaustion, physical weakness, cardiovascular problems, emotional lability and irritability, concentration difficulties, and other decrements in cognitive function,13 suggesting a disorder similar to chronic fatigue syndrome and including both psychological and physiological symptoms. Interdisciplinary research is needed to better understand and document the etiology of this condition and to inform the development of effective countermeasures. In addition, the development of strategies for managing agitation is particularly important for long-duration flight in tightly confined quarters.
As missions extend beyond low Earth orbit, crews will become more autonomous, and two-way communication with Earth will be delayed (around 40 min for signals sent from Mars). Consequently, direct communication between a troubled crew member and a mental health specialist will become increasingly difficult as missions travel farther from Earth. It is therefore necessary to develop alternative, evidence-based, effective methods to prevent or alleviate mental health problems. Computer-interactive intervention and treatment programs may be
more “user friendly” for astronauts than self-disclosure of personal problems by talking with a specialist. Treatment outcome and follow-up findings demonstrate that computer-based cognitive behavior therapy and other types of problem-solving intervention programs, either free-standing or with minimal additional therapist input, have proven effective.14 Research is underway to develop multimedia computer-based, self-directed treatment programs for astronauts to autonomously manage problems with depression,15 stress, and anxiety.16 It is important to bring the programs to a technology readiness level (TRL) that will enable effectiveness to be systematically evaluated in comparative treatment outcome studies.
Psychoactive medications have been part of the formulary used onboard crewed space vehicles.17 Indeed, diverse drugs acting on the central nervous system (sedative hypnotics, anxiolytics, anti-nausea agents) are the most widely used medications consumed in space. However, physiological changes due to microgravity and other effects of space may change the pharmacokinetic characteristics of medications, influencing both dosage and route of administration. These possibilities need to be studied more fully.
Also, recent medical research shows that efficacy of interventions and therapies can sometimes be enhanced by taking into account individual differences among patients. For example, increased efficacy can sometimes be achieved by customizing medications based on the individual patient’s genetic profile.18 It is likely that similar benefits will accrue with development of empirically validated, individually tailored countermeasures to prevent or mitigate psychological dysfunctions during space missions.
Integrating behavioral health evaluations into the annual flight physical examination could help identify, and perhaps even prevent, behavioral and mental health problems and would support the astronaut throughout his/her career.19 Routine psychological evaluations may also enhance participation in behavioral research by virtue of familiarizing astronaut personnel with the nature and importance of these issues and concomitantly reducing the stigma associated with them. The post-flight period can be particularly stressful; post-flight personality changes have been reported, although in both positive and negative directions. In addition, it is important to provide psychosocial support to the astronaut’s family. More comprehensive data are needed to assess the long-term psychological health of the astronaut and family.
1. Mission performance measures should be developed and empirically evaluated to provide criteria for assessing optimal functioning on exploration missions. The required research could be completed in the near term if personality data already collected from the NASA space program are used in addition to current data. Such research enables space missions.
2. To improve the selection process, a standardized core battery of robust psychological measures with established reliability and validity should be developed with adequate norms for each nation participating in exploration missions. The test battery should assess both personality and social skill characteristics and pay greater attention to the assessment of personality patterns. This research enables space missions.
3. Mission control personnel should also complete the personality test battery. Their test results will contribute to a scientific understanding of individual characteristics that influence the interactions between space crews and ground personnel and the consequent effects on mission performance, particularly under conditions of high autonomy. This research enables space missions.
4. Comprehensive training programs should be developed and standardized to provide and empirically assess the effectiveness of stress management and other training procedures for astronauts, mission control personnel, and family members across all phases of the mission, including the post-mission period. Such research enables space missions.
5. Interdisciplinary research should be undertaken to better understand asthenia and to develop and assess the effectiveness of countermeasures to prevent or alleviate this condition. This research both enables and is enabled by space missions.
6. Additional research should be performed to study the biological and psychological factors that mediate adaptation and psychological resilience to the space environment. This research both enables and is enabled by space missions.
7. The influence of microgravity on the psychopharmacology, efficacy, and side effect profile of psychoactive medications should be studied. Recent findings suggest a genetic basis for individual differences in the pharmacokinetic profile of certain drugs. For example, the apolipoprotein E epsilon 4 variant, which is a known marker for susceptibility to Alzheimer’s disease, is also associated with relatively exaggerated cognitive impairment following administration of benzodiazepines—a class of medications that is frequently used in space.20 This research both enables and is enabled by space missions.
8. Research should be conducted to identify and prevent or mitigate decrements in individual functioning. The effectiveness of verbal content analysis and other telemedicine-based techniques to identify stress and the development of mental disorders and to treat them through onboard counseling or computer-interactive programs should be studied. A variety of computer-interactive intervention programs should be developed and compared in head-to-head trials to identify the most effective and astronaut-compatible programs for use in space. Systematic research needs to be conducted during space missions and in analog environments to evaluate the effectiveness of the currently available prevention and intervention programs, with development of new, astronaut-specific versions/programs as needed. This research both enables and is enabled by space missions.
9. In addition to astronauts, future crewed space activities may include space tourists or scientific payload specialists. Careful attention should be given to selection characteristics of such individuals as well as to the extent of their training for the space environment. While some guidelines are currently available for short-term space tourists, it is likely that more stringent selection criteria and training will be necessary for non-astronaut crew who are participating in longer space missions.
In the 2001 Institute of Medicine report Safe Passage: Astronaut Care for Exploration Missions,21 the following was noted: “Perhaps the matter of highest priority in the performance and general living conditions domain is the development of an evidence-based approach to the management of harmonious and productive, small, multinational groups who must live and work together in isolated, confined, and hazardous environments” (p. 145). Factors that mediate group functioning are depicted in Figure 5.2.
Despite the progress made in the past decade, continued research is required to identify individual, interpersonal, cultural, and environmental determinants of crew cohesion, crew performance, and ground-crew interaction and to develop and evaluate evidence-based programs and interventions that promote optimal group functioning and prevent threats to crew cohesion and productivity.
Analog studies and surveys of astronaut personnel have identified individual characteristics that are predictors of social compatibility. These positive characteristics include low extraversion and high introversion,22 high positive instrumentality (goal-oriented, active, self-confident), high expressiveness (kind, aware of others’ feelings), low negative instrumentality (not arrogant, hostile, boastful, egotistical), and low communion (self-subordinating, subservient, unassertive).23,24 However, more research is required to determine the influence of individual personality and performance on group functioning and vice versa.25 In this regard, there is considerable overlap between research to be conducted on group functioning and research on individual functioning. Such research would include observational and experimental studies of the phenomena of “approach and avoidance”—i.e., when do individual crew members need to be a part of the larger group, and when should they be apart from the group? A better understanding of strategies for dealing with crew-imposed ostracism and marginality or self-imposed isolation and withdrawal is also required, since such understanding will be the key to development of effective countermeasures that promote crew cohesion and prevent conflict.
A number of important social characteristics that affect group functioning in space have been identified. One factor relates to the homogeneity and heterogeneity of crews with respect to social (e.g., age, gender, cultural background), psychological (need for achievement, aggressiveness, autonomy), and other (e.g., interest in leisure activities) characteristics that have been shown to predict crew cohesion and conflict, team decision making, and response to crises. For example, as noted by Kanas and colleagues,26 in a situation where astronauts from one country are treated as guests in a facility or craft that is nominally under control of another (host) country, such individuals may feel subordinate and marginalized, leading to increased tension, reduced communication, and increased risk of failing to appropriately coordinate activities when performing routine assignments or responding to crises.27
Crews of future long-duration missions (whether for exploration or colonization) will most likely be composed of a heterogeneous mix of national, organizational, and professional cultures. Studies of cultural issues that may enhance or degrade performance among such blended groups are scarce to nonexistent. Because of large cultural differences in preferred leadership styles among likely mission participants, the question of how to optimize leadership for such a group in isolation is critical.
Culture, often described as the software of the mind, is a major determinant of performance and adjustment behavior in endeavors that require individuals to work harmoniously in teams, especially under conditions of isolation and danger.28 Three kinds of cultures have been identified: national, organizational, and professional. National cultures are the internalized attitudes and normative beliefs associated with being a citizen of a particular country. Organizational cultures consist of norms and practices associated with membership in an organization such as a space agency or research group. Finally, professional cultures are those norms and practices internalized when achieving membership in an occupation such as physician, scientist, engineer, or astronaut.
National culture is likely to be influential in long-duration spaceflight or colonization with crews of diverse origin. Differences in organizational and professional cultures are also likely to mediate team performance. Helmreich and Merritt29 examined cultural dimensions in organization groups such as pilots and physicians. Their results confirmed the ubiquity of cultural dimensions revealing, for example, a professional culture in medicine that stresses the need for perfection and a strong denial of the effects of stress and fatigue on performance. NASA and other space agencies have their own organizational cultures and, of course, contain diverse professional cultures, including those of astronauts and ground personnel.
Some characteristics likely to influence group functioning are environmental in nature. Such features may include the physical environment (e.g., a lunar or martian base, spacecraft) and the organizational environment (e.g., military versus civilian control, multinational administration versus administration by predominately one organization or nation). One salient aspect of the organizational environment noted in the Safe Passage report is crew autonomy: the extent to which crews will be required to, or allowed to, act as autonomous entities.30 The degree of crew autonomy will vary as a function of mission parameters (e.g., distance from Earth, length of time) and the ability of ground control systems to provide and offer timely support to the crew. However, other factors—such as the individual need for control, expression of crew hostility and stress displaced to mission control personnel, and the benefits of autonomy for team-building—must also be considered in both planning for autonomy and developing training programs to promote autonomy.
Leadership is a critical predictor of team functioning in isolated and confined environments. Leadership issues are intimately connected with issues of crew autonomy,31 and leadership style is significantly associated with measures of team cohesion and conflict.32,33,34 However, additional research is required to determine whether cultural differences in the exercise of leadership are likely to produce crew tension when leaders and followers belong to different cultural groups. Additional research is also required to determine whether distributed leadership in the form of team decision making is facilitated by homogeneous crews that foster cohesion and reduce conflict or by heterogeneous crews that avoid groupthink and are therefore more likely to produce innovative solutions in emergencies.
Research is needed to develop additional, robust measures of group processes that provide specificity and sensitivity to subtleties of group interactions and their effects on team performance. A balance of research in naturally occurring analog settings (e.g., polar and undersea research facilities) and rigorously designed experimental simulations (e.g., long-duration chamber studies) that faithfully mirror actual mission parameters (e.g., isolation, confinement, workload, long and uncertain duration, communication delays, disruption of diurnal sleep-wake cycles) will be critical.
Development of evidence-based countermeasures designed to facilitate group functioning and prevent decrements in group functioning due to inadequate communication and coordination or due to increased tension and conflict will remain a high priority for the next decade. The issue of crew member selection also remains a primary focus, as there are currently no evidence-based guidelines for selection of individuals who will be expected to live and work together for extended periods of time. Presumably, many of the requirements for the development of such guidelines will come from studies in which optimally and non-optimally functioning crews are compared. Characteristics that distinguish crew members from one another (age, gender, cultural background, personality, interest in leisure activities) and characteristics that make crew members similar (mission identity, shared sense of purpose, socioeconomic status) are likely to be important. Identification of individual characteristics associated with the assumption of statuses and roles that facilitate or promote group cohesion (i.e., a mediator or culture broker) or exacerbate group conflict (i.e., by an instigator or nonconformist) will also be necessary.
Evidence-based training programs are needed to promote behaviors that facilitate crew cohesion, conflict management, and utilization of prosocial skills under conditions of prolonged isolation and confinement. Some training may involve adaptation and evaluation of existing evidence-based practices like social-skills training under a specific set of circumstances (long-duration missions characterized by prolonged isolation and confinement).
For instance, social-skills training may include modules that enable astronauts to identify when to approach other crew members to address individual or group decrements in performance and when to avoid such interactions.
Although a number of multinational, multicultural organizations have instituted training programs to increase cultural awareness and help personnel deal with potential cultural conflicts, the efficacy of these programs has not been well validated.
Finally, more research on noninvasive techniques for monitoring group functioning and administration of support to ensure optimal functioning during extended-duration missions is recommended. Strategies for assessing and monitoring the status and performance of individual crew members should be complemented by strategies for assessing and monitoring team performance.
To achieve an understanding of fundamental mechanisms underlying group functioning that will be critical to the success of long-duration missions and to facilitate development of countermeasures that promote optimal group functioning and prevent or defuse group tension and conflict that might lead to a decline in performance, the panel offers the following recommendations:
1. NASA should develop new or adapt existing evidence-based tools for crew selection and for training astronauts to assume roles that facilitate crew cohesion, conflict management, and utilization of social skills under conditions of prolonged isolation and confinement. This research both enables and is enabled by space missions.
2. Research should be conducted to identify individual, interpersonal, cultural, and environmental determinants of crew cohesion, crew performance, and ground-crew interaction. Such determinants include but are not limited to the reciprocal influence of individual personality and performance on group functioning; the phenomena of approach and avoidance and strategies for dealing with crew-imposed ostracism and marginality or self-imposed isolation and withdrawal; heterogeneous and homogeneous social, personality, and cultural characteristics of crew members associated with optimally functioning crews; the costs and benefits to group functioning of crew heterogeneity, formation of dyads or subgroups on the basis of shared interests, and increased crew autonomy; the impact of cultural differences in the exercise of leadership on crew cohesion and tension; and crew size dynamics for both smaller (n = 3) and larger crews. The efficacy of cultural training programs should be investigated using multicultural teams as subjects in relevant environments. This research both enables and is enabled by space missions.
3. Development should be undertaken of additional, robust measures of group processes that could provide greater sensitivity and specificity in the measurement of the subtleties of group interactions and their relationships to team performance. Such measures could be employed to identify potential problems early and facilitate the timing of interventions to prevent frictions from escalating into overt problems. This line of research both enables and is enabled by space missions.
4. NASA should develop a balanced research portfolio in analog settings (e.g., the ISS, polar and undersea research facilities) and rigorously designed experimental simulations (e.g., long-duration chamber studies) that faithfully mirror actual space mission parameters (e.g., isolation, confinement, workload, long and uncertain duration, communication delays, disruption of diurnal sleep-wake cycles). This research enables space missions. This research in analog environments can be accomplished in the intermediate term, that is, the next 3 to 5 years. The ISS also offers several advantages that allow it to function as an analog setting for future expeditionary missions to the Moon or Mars, including small crews of similarly trained and employed individuals and prolonged exposure to microgravity and radiation.
5. Development and validation should be conducted for noninvasive techniques for monitoring group functioning and support to ensure optimal functioning during extended-duration missions. This research enables space missions.
Historically, NASA has recognized the importance of sleep and circadian rhythms for the sustainment of cognitive functioning and has funded and conducted seminal studies in the relevant areas of sleep loss, circadian rhythms,
alertness, and performance. Studies including objective measures of sleep (i.e., polysomnography and/or wrist actigraphy) have generally revealed that sleep is altered during space missions, with reduced sleep duration35-38 and evidence of circadian desynchrony39,40,41 that may become more severe as the duration of the space mission is extended (beyond 90 days).42 Consistent with these findings, sleep architecture has been found to be affected during spaceflight, with some studies showing a shift in the timing of slow wave (deep) sleep toward the latter third of the sleep period43,44 and others finding reduced slow wave sleep during the last third of the sleep period.45 Rapid eye movement (REM) sleep is also affected, with reduced REM onset latency46,47 and an increased amount of stage REM sleep upon return to Earth (i.e., evidence of possible REM rebound, which typically occurs in response to REM deprivation).48 Subjective ratings of fatigue have been found to increase during some spaceflights,49,50 but subjective fatigue is not always evident during space missions.51 This discrepancy may reflect variations in the intensity and timing of operational demands across missions (factors that can mediate sleep duration, timing, and quality in operational environments on Earth as well), suggesting that at least some sleep and circadian rhythm-related disturbances during space missions may be amenable to work scheduling-related interventions.52
A variety of neurobehavioral performance deficits have been found during spaceflight, and those deficits have clear implications for astronaut safety and mission success (for a review, see Mallis and DeRoshia53). Although it is difficult to specify the extent to which sleep loss and fatigue have contributed to actual errors and accidents during missions in space, sleep loss and fatigue have been recognized as likely contributory factors in incidents such as the Mir-Progress collision on June 25, 1997.54
NASA’s long-term focus on sleep research has been, and remains, appropriate since it is clear that adequate sleep, by means of physiological processes that are not yet understood, constitutes a necessary precondition for normal cognitive functioning—and thus for safe and successful space exploration.
Prior studies have shown that performance on a variety of cognitive tasks ranging from simple reaction time to situation awareness and problem solving varies as a function of sleep duration, time since awakening, and phase of the circadian rhythm of alertness.55 The biochemical processes that underlie the alertness and cognitive performance deficits that accrue with acute sleep loss—and the complementary biochemical processes by which alertness and mental agility are restored during subsequent sleep—are as yet unknown.56 However, functional brain imaging studies have shown that sleepiness is characterized by deactivation of regional brain activity, with the greatest deactivations occurring in the thalamus (which mediates alertness and attention); the inferior parietal/superior temporal cortex (a heteromodal association area that mediates arithmetic problem solving); and, most notably, the prefrontal cortex, which mediates virtually all higher-order mental abilities including judgment, planning, and problem solving (see Figure 5.3).57 It is clear that such regional deactivations underlie, or at least reflect, specific performance deficits, since it is possible to actually predict specific sleep-loss-induced performance deficits based on this pattern of regional brain deactivation.58
Many sleep-loss studies have been conducted over the past century. Typically, the behavioral and physiological effects of one to three nights without any sleep (total sleep deprivation) were measured in these studies. However, only recently have the potential effects of chronic (weeks, months, or longer) sleep restriction become a focus of scientific research—despite the fact that chronic sleep restriction is far more prevalent, and therefore potentially a bigger problem, than total sleep deprivation in both Earth- and space-based operational environments.
Although relatively few in number, sleep restriction studies have revealed two important consequences: First, subjects do not realize that their performance is affected—i.e., subjective habituation to chronically inadequate sleep can occur—although no objective adaptation occurs and their cognitive performance and alertness remain decremented for the duration of the sleep restriction period.59 Second, long-term changes occur in brain physiology and hormonal profiles, and these changes can have potentially detrimental effects on health. For example,
evidence is accruing that individuals who habitually get less sleep tend to gain weight faster, which is thought to be the result of sleep-restriction-induced changes in leptin and ghrelin levels and a slowed metabolic rate.60
Clearly, adequate sleep is a basic physiological need that is necessary for sustaining optimal mental functioning. During extended space missions, adequate sleep will therefore be part of the foundation that must be maintained to ensure that crew members are at least nominally prepared to deal with those challenges requiring cognitive agility and astuteness.
The potential effects of chronic sleep loss on those aspects of cognitive functioning that mediate individual and group functioning (cohesiveness and cooperation) are less clear than the effects on alertness and simple cognitive processes discussed above. Because group cohesion and cooperation will be far more challenging to sustain during extended-duration space missions, research that explores these effects will be particularly important during the next decade.
Sleep disturbance is a common complaint in (and perhaps an integral component of) disorders such as depression and post-traumatic stress disorder (PTSD). In fact, sleep disturbance is among the most common complaints of PTSD patients.61 However, it is not yet known whether chronic sleep disturbance prior to stressor exposure sensitizes individuals (thus making them more susceptible to developing PTSD) and/or whether PTSD-associated sleep disturbance exacerbates symptoms and interferes with recovery.
Of particular interest is the possibility that chronic sleep difficulties in space could lower psychological resil-
ience and increase the incidence of stressor-induced psychophysiological symptoms/problems such as asthenia. Among the arguments in favor of this hypothesis are that (1) emotional lability is a prominent symptom of asthenia (and a known effect of sleep loss)62 and (2) increased ambient light intensity (which could strengthen the circadian rhythm of alertness) is thought to help reverse symptoms of asthenia.
1. NASA should continue to support studies to determine and quantify the extent to which sleep plays a role in maintaining mental, physical, and cognitive resilience during space missions and the extent to which sleep-enhancing interventions reverse stress-related symptoms and restore or sustain mental resilience. This research both enables and is enabled by space missions. In addition, this research can be accomplished in the short term.
2. Given the importance of sleep for sustaining cognitive performance, NASA should support research to determine whether stressors unique to the space environment impact restorative sleep processes, and if so, to what extent. Stressors of interest include, but are not limited to, microgravity, exposure to radiation, environmental pollution, and lack of privacy/personal space. This research both enables and is enabled by space missions.
3. NASA should support research to determine the efficacy of interventions (both pharmacological and nonpharmacological) for improving and sustaining adequate sleep in the space environment. This research both enables and is enabled by space missions.
4. NASA should sponsor research to determine the utility of sleep monitoring during extended missions in space. Sleep not only impacts mental state and cognitive abilities but also can be a sensitive barometer that reflects emotional health status. This research is important to ensure that adequate sleep is obtained and also to gauge how well astronauts are coping with stressors during missions of extended duration. This research both enables and is enabled by space missions.
5. Comprehensive, multidisciplinary, extended-duration simulation studies in the ISS and/or in high-fidelity analog settings should be conducted to determine and model the potentially complex, bidirectional interactions among sleep, cognitive functioning, individual functioning, and group dynamics. These variables will ultimately determine the chances for success in extended-duration space missions. This research enables space missions.
6. Sleep-related research programs should continue to explore the physiological mechanisms by which exposure to light resets and maintains the circadian rhythm of alertness and sleep/wake cycles. Alignment with current and future NASA missions and goals should be considered. This research enables space missions.
Research imperatives for the next decade should include studies aimed at (1) determining the potential effects of stressors likely to be encountered during extended space missions, alone and in combination, on astronauts’ general psychological and physical well-being—with particular emphasis on sustaining astronauts’ capacity to perform mission-related tasks, both as individuals and as members of a team; and (2) developing interventions to prevent, minimize, or reverse deleterious effects of such stressors.
The panel selected and prioritized the following recommendations on the basis of (1) a logical progression from assessment to monitoring to intervention and (2) the level of existing knowledge and potential for important discoveries. In particular, research is needed to look at the interactive effects of all space exploration-relevant stressors on the psychological status and performance of astronauts. Although such studies are logistically difficult, they are critical for understanding and predicting stress in astronauts and for devising and testing interventions. Recommendations 1, 2, and 3 enable space missions. Recommendation 4 both enables and is enabled by space missions.
1. Development of sensitive, meaningful, and valid measures of mission-relevant performance for both astronauts and mission control personnel. A combination of embedded performance measures (e.g., indicators of performance capacity that are maximally unobtrusive by virtue of being obtained/monitored during completion of actual mission-related tasks) and sensitive, well-validated (against actual mission tasks) cognitive tests is a basic requirement. This major gap in assessment must be filled in order to achieve both the research-related
goals of understanding and quantifying the effects of stressors on mission-critical performance capacity and the mission-related need for sensitive tools to monitor cognitive performance, detect problems, and facilitate timely and effective interventions. It is estimated that significant progress toward accomplishment of this research goal could be achieved in 2 to 5 years. (B1)
2. Integrated translational research in which long-duration missions are simulated (in analogs or on the ISS) specifically for the purpose of studying interrelationships among individual functioning, cognitive performance, sleep, and group dynamics. The ultimate research aim would be to build predictive models of astronaut performance and well-being during extended missions in space that can be used to plan and manage such missions. It is estimated that significant progress toward accomplishment of this research goal could be achieved in 5 to 8 years. (B2)
3. Research to determine genetic, physiological (e.g., sleep-related), and psychological underpinnings of individual differences in resilience to stressors during extended missions in space, with development of an “individualized medicine-like” approach to sustaining astronauts during such missions. It is estimated that significant progress toward accomplishment of this research goal could be achieved in 5 to 10 years. (B3)
4. Research to enhance the cohesiveness, team performance, and effectiveness of multinational crews, especially under conditions of extreme isolation and autonomy. It is estimated that significant progress toward accomplishment of this research goal could be achieved in 2 to 5 years. (B4)
The preceding estimates of time required to achieve significant scientific progress are based on the presumption that most astronauts will agree to participate in the relevant studies. More detailed research priorities within the areas of cognitive performance, sleep, individual functioning, and group functioning are described elsewhere in this chapter.
1. U.S. Human Spaceflight Plans Committee. 2009. Seeking a Human Spaceflight Program Worthy of a Great Nation. NASA, Washington, D.C. Available at http://www.nasa.gov/pdf/396117main_HSF_Cmte_FinalReport.pdf.
3. Stern, Y. 2009. Cognitive reserve. Neuropsychologia 47(10):2015-2028.
4. Mallis, M.M., and DeRoshia, C.W. 2005. Circadian rhythms, sleep, and performance in space. Aviation, Space, and Environmental Medicine 76(6 Suppl.):B94-B107.
5. Mallis, M.M., and DeRoshia, C.W. 2005. Circadian rhythms, sleep, and performance in space. Aviation, Space, and Environmental Medicine 76(6 Suppl.):B94-B107.
6. National Research Council. 1998. A Strategy for Research in Space Biology and Medicine into the Next Century. National Academy Press, Washington, D.C.
7. Leon, G.R. 2008. Strategies to optimize individual and team performance. Proceedings of the 3rd International Association for the Advancement of Space Safety Conference (IAASS). October 22, 2008, Rome, Italy. International Association for the Advancement of Space Safety, Noordwijk, The Netherlands.
8. Kanas, N., Sandal, G.M., Boyd, J.E., Gushin, V.I., Manzey, D., North, R., Leon, G.R., Suedfeld, P., Bishop, S., Fiedler, E.R., Inoue, N., et al. 2009. Psychology and culture during long-duration space missions. Acta Astronautica 64:659-677.
9. Institute of Medicine. 2001. Safe Passage: Astronaut Care for Exploration Missions. National Academy Press, Washington D.C.
10. Palinkas, L.A., and Suedfeld, P. 2008. Psychological effects of polar expeditions. Lancet 371(9607):153-163.
11. Kanas, N., and Manzey, D. 2008. Space Psychology and Psychiatry. 2nd Edition. Microcosm Press, El Segundo, Calif., and Springer, Dordrecht, The Netherlands.
12. Gushin, V.I., Institute for Biomedical Problems (Russia), communication to the National Research Council’s Human Behavior and Mental Health Panel via teleconference, December 15, 2009.
13. Myasnikov, V.I., and Zamaletdinov, I.S. 1996. Psychological states and group interactions of crew members in flight. Pp. 419-432 in Space Biology and Medicine III: Humans in Spaceflight (C.S. Leach Huntoon, A.E. Nicogossian, V.V. Antipov, and A.E. Grigoriev, eds.). American Institute of Aeronautics and Astronautics, Reston, Va.
14. Gega, L., Marks, I., and Mataix-Cols, E. 2004. Computer-aided CBT self-help for anxiety and depressive disorders: Experience of a London clinic and future directions. Journal of Consulting and Clinical Psychology 60:147-157.
15. Carter, J.A., Buckey, J.C., Greenhalgh, L., Holland, A.W., and Hegel, M.T. 2005. An interactive media program for managing psychosocial problems spaceflights. Aviation, Space, and Environmental Medicine 76(6 Suppl.):B213-B223.
16. Craske, M.G., Rose, R.D., Lang, A., Welch, S.S., Campbell-Sills, L., Sullivan, G., Sherbourne, C., Bystritsky, A., Stein, M.B., and Roy-Byrne, P.P. 2009. Computer-assisted delivery of cognitive behavioral therapy for anxiety disorders in primary-care settings. Depression and Anxiety 26:235-242.
17. Saivin, S., Pavy-Le Traon, A., Soulez-LaRiviere, C., Guell, A., and Houin, G. 1997. Pharmacology in space: Pharmacokinetics. In Advances in Space Biology and Medicine (S.L. Bonting, ed.). Volume 6. JAI Press, Greenwich, Conn.
18. Langreth, R., and Waldholz, M. 1999. New era of personalized medicine: Targeting drugs for each unique genetic profile. Oncologist 4(5):426-427.
19. NASA. 2007. NASA Astronaut Health Care System Review Committee Report to the Administrator. February-June. Available at http://www.nasa.gov/pdf/183113main_NASAhealthcareReport_0725FINAL.pdf.
20. Pomara, N., Willoughby, L., Wesnes, K., Greenblatt, D.J., and Sidtis, J.J. 2005. Apolipoprotein E epsilon4 allele and lorazepam effects on memory in high-functioning older adults. Archives of General Psychiatry 62(2):209-216.
21. Institute of Medicine. 2001. Safe Passage: Astronaut Care for Exploration Missions. National Academy Press, Washington D.C.
22. Palinkas, L.A., and Suedfeld, P. 2008. Psychological effects of polar expeditions. Lancet 371(9607):153-163.
23. Rose, R.M., Fogg, L.F., Helmreich, R.L., and McFadden, T. 1994. Psychological predictors of astronaut effectiveness. Aviation, Space, and Environmental Medicine 65:910-915.
24. McFadden, T.J., Helmreich, R.L., Rose, R.M., and Fogg, L.F. 1994. Predicting astronauts’ effectiveness: A multivariate approach. Aviation, Space, and Environmental Medicine 65:904-909.
25. Palinkas, L.A., Gunderson, E.K.E., Holland, A.W., Miller, C., and Johnson, J.C. 2000. Predictors of behavior and performance in extreme environments: The Antarctic Space Analogue Program. Aviation, Space, and Environmental Medicine 71:619-625.
26. Kanas, N., Sandal, G.M., Boyd, J.E., Gushin, V.I., Manzey, D., North, R., Leon, G.R., Suedfeld, P., Bishop, S., Fiedler, E.R., Inoue, N., et al. 2009. Psychology and culture during long-duration space missions. Acta Astronautica 64:659-677.
27. Gushin, V.I., Efimov, V.A., Smirnova, T.M., Vinokhodova, A.G., and Kanas, N. 1998. Subject’s perception of the crew interaction dynamics under prolonged isolation. Aviation, Space, and Environmental Medicine 69:556-561.
28. Kanas, N. 2009. Psychology and Culture During Long-Duration Space Missions. International Academy of Astronautics, Paris, France.
29. Helmreich, R.L., and Merritt, A. 1999. Culture at Work in Aviation and Medicine. Ashgate, New York.
30. Institute of Medicine. 2001. Safe Passage: Astronaut Care for Exploration Missions. National Academy Press, Washington D.C., pp. 146-147.
31. Kanas, N., Sandal, G.M., Boyd, J.E., Gushin, V.I., Manzey, D., North, R., Leon, G.R., Suedfeld, P., Bishop, S., Fiedler, E.R., Inoue, N., et al. 2009. Psychology and culture during long-duration space missions. Acta Astronautica 64:659-677.
32. Blair, S.M. 1992. Community Organization Under Differing South Pole Leaders. AIAA 92-1528. American Institute of Aeronautics and Astronautics, Washington, D.C.
33. Johnson, J.C., Palinkas, L.A., and Bosterm, J.S. 2003. Informal social roles and the evolution and stability of social networks. Pp. 121-132 in Dynamic Social Network Modeling and Analysis: Workshop Summary and Papers (R. Breiger, K. Corley, and P. Pattison, eds.). The National Academies Press, Washington, D.C.
34. Kanas, N.A., Salnitskiy, V.P., Boyd, J.E., Gushin, V.I., Weiss, D.S., Saylor, S.A., Kozerenko, O.P., and Marmar, C.M. 2007. Crewmember and mission control personnel interactions during International Space Station missions. Aviation, Space, and Environmental Medicine 78:601-607.
35. Dijk, D.J., Neri, D.F., Wyatt, J.K., Ronda, J.M., Riel, E., Ritz-De Cecco, A., Hughes, R.J., Elliott, A.R., Prisk, G.K., West, J.B., and Czeisler, C.A. 2001. Sleep, performance, circadian rhythms, and light-dark cycles during two space shuttle flights. American Journal of Physiology. Regulatory, Integrative and Comparative Physiology 281(5):R16747-R16764.
36. Monk, T.H., Buysse, D.J., Billy, B.D., Kennedy, K.S., and Willrich, L.M. 1998. Sleep and circadian rhythms in four orbiting astronauts. Journal of Biological Rhythms 13(3):188-201.
37. Gundel, A., Nalashiti, V., Reucher, E., and Zulley, J. 1993. Sleep and circadian rhythm during a short space mission. Clinical Investigation 71(9):718-724.
38. Gundel, A., Polyakov,V.V., and Zulley, J. 1997. The alterations of human sleep and circadian rhythms during spaceflight. Journal of Sleep Research 6(1):1-8.
39. Dijk, D.J., Neri, D.F., Wyatt, J.K., Ronda, J.M., Riel, E., Ritz-De Cecco, A., Hughes, R.J., Elliott, A.R., Prisk, G.K., West, J.B., and Czeisler, C.A. 2001. Sleep, performance, circadian rhythms, and light-dark cycles during two space shuttle flights. American Journal of Physiology. Regulatory, Integrative and Comparative Physiology 281(5):R16747- R16764.
40. Monk, T.H., Kennedy, K.S., Rose, L.R., and Linenger, J.M. 2001. Decreased human circadian pacemaker influence after 100 days in space: A case study. Psychosomatic Medicine 63(6):881-885.
41. Gundel, A., Polyakov, V.V., and Zulley, J. 1997. The alterations of human sleep and circadian rhythms during spaceflight. Journal of Sleep Research 6(1):1-8.
42. Monk, T.H., Kennedy, K.S., Rose, L.R., and Linenger, J.M. 2001. Decreased human circadian pacemaker influence after 100 days in space: A case study. Psychosomatic Medicine 63(6):881-885.
43. Gundel, A., Nalashiti, V., Reucher, E., and Zulley, J. 1993. Sleep and circadian rhythm during a short space mission. Clinical Investigation 71(9):718-724.
44. Gundel, A., Polyakov, V.V., and Zulley, J. 1997. The alterations of human sleep and circadian rhythms during spaceflight. Journal of Sleep Research 6(1):1-8.
45. Dijk, D.J., Neri, D.F., Wyatt, J.K., Ronda, J.M., Riel, E., Ritz-De Cecco, A., Hughes, R.J., Elliott, A.R., Prisk, G.K., West, J.B., and Czeisler, C.A. 2001. Sleep, performance, circadian rhythms, and light-dark cycles during two space shuttle flights. American Journal of Physiology. Regulatory, Integrative and Comparative Physiology 281(5):R16747- R16764.
46. Gundel, A., Nalashiti, V., Reucher, E., and Zulley, J. 1993. Sleep and circadian rhythm during a short space mission. Clinical Investigation 71(9):718-724.
47. Gundel, A., Polyakov, V.V., and Zulley, J. 1997. The alterations of human sleep and circadian rhythms during spaceflight. Journal of Sleep Research 6(1):1-8.
48. Dijk, D.J., Neri, D.F., Wyatt, J.K., Ronda, J.M., Riel, E., Ritz-De Cecco, A., Hughes, R.J., Elliott, A.R., Prisk, G.K., West, J.B., and Czeisler, C.A. 2001. Sleep, performance, circadian rhythms, and light-dark cycles during two space shuttle flights. American Journal of Physiology. Regulatory, Integrative and Comparative Physiology 281(5):R16747- R16764.
49. Dijk, D.J., Neri, D.F., Wyatt, J.K., Ronda, J.M., Riel, E., Ritz-De Cecco, A., Hughes, R.J., Elliott, A.R., Prisk, G.K., West, J.B., and Czeisler, C.A. 2001. Sleep, performance, circadian rhythms, and light-dark cycles during two space shuttle flights. American Journal of Physiology. Regulatory, Integrative and Comparative Physiology 281(5):R16747- R16764.
50. Kelly, T.H., Heinz, R.D., Zarcone, T.J., Wurster, R.M., and Brady, J.V. 2005. Crewmember performance before, during, and after spaceflight. Journal of the Experimental Analysis of Behavior 84(2):227-241.
51. Monk, T.H., Buysse, D.J., Billy, B.D., Kennedy, K.S., and Willrich, L.M. 1998. Sleep and circadian rhythms in four orbiting astronauts. Journal of Biological Rhythms 13(3):188-201.
52. Stampi, C. 1994. Sleep and circadian rhythms in space. Journal of Clinical Pharmacology 34(5):518-534.
53. Mallis, M.M., and DeRoshia, C.W. 2005. Circadian rhythms, sleep, and performance in space. Aviation, Space, and Environmental Medicine 76(6 Suppl.):B94-B107.
54. Ellis, S.R. 2000. Collision in space. Ergonomics in Design: The Magazine of Human Factors Applications 8(1):4-9.
55. See, for example, T.J. Balkin, T. Rupp, D. Picchioni, and N.J. Wesensten, Sleep loss and sleepiness: Current issues, Chest 134(3):653-660, 2008.
56. Siegel, J.M. 2005. Clues to the functions of mammalian sleep. Nature 37(7063):1264-1271.
57. Thomas, M., Sing, H., Belenky, G., Holcomb, H., Mayberg, H., Dannals, R., Wagner, H., Thorne, D., Popp, K., Rowland, L., Welsh, A., Balwinski, S., and Redmond, D. 2000. Neural basis of alertness and cognitive performance impairments during sleepiness. I. Effects of 24 h of sleep deprivation on waking human regional brain activity. Journal of Sleep Research 9(4):335-352.
58. See, for example, W.D. Killgore, T.J. Balkin, and N.J. Wesensten, Impaired decision making following 49 h of sleep deprivation, Journal of Sleep Research 15:7-13, 2006; and W.D. Killgore and S.A. McBride, Odor identification accuracy declines following 24 h of sleep deprivation, Journal of Sleep Research 15:111-116, 2006.
59. Belenky, G.L., Wesensten, N.J., Thorne, D., Thomas, M., Sing, H., Redmond, D.P., Russo, M.B., and Balkin, T.J. 2003. Patterns of performance degradation and restoration during sleep restriction and subsequent recovery: A sleep dose-response study. Journal of Sleep Research 12:1-12.
60. Leproult, R., and Van Cauter, E. 2010. Role of sleep and sleep loss in hormonal release and metabolism. Endocrine Development 17:11-21.
61. Neylan, T.C., Marmar, C.R., Metzler, T.J., Weiss, D.S., Zatzick, D.F., Delucchi, K.L., Wu, R.M., and Schoenfeld, F.B. 1998. Sleep disturbances in the Vietnam generation: Findings from a nationally representative sample of male Vietnam veterans. The American Journal of Psychiatry 155:929-933.
62. Meerlo, P., Sgoifo, A., and Suchecki, D. 2008. Restricted and disrupted sleep: Effects on autonomic function, neuroendocrine stress systems and stress responsivity. Sleep Medicine Reviews 12(3):197-210.
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