Life on Earth has developed to be in tune with the cycles of daylight and darkness that stem from our planet's 24 hour rotation. Like other animals, human beings have an internal biological "clock" which acts as a biological timekeeper. For diurnal creatures like ourselves, the clock prepares the body and mind for restful sleep at night and active wakefulness during the day. The clock also regulates many, if not all, essential body functions such as body temperature, glandular secretion, heart rate and urine excretion to name a few. This clock is referred to as the Circadian Timing System (CTS) and requires time cues from the environment in order to keep it synchronized with the 24 hour rotation of the Earth.

This experiment, which consisted of three sleep investigations combined into one experiment, was designed to study the effects of space flight on the CTS of crewmembers before, during, and after space flight. Sleep patterns and reports on crewmember dreams were recorded over a prolonged exposure to microgravity. These data were correlated with physiological adaptations to microgravity. Changes in rapid eye movement (REM) sleep with adaptation to microgravity and readaptation to a 1-G environment were studied. This study also explored specific biochemical changes in the immune system during sleep, and how they are affected in microgravity.

Experiment Objectives

A. Human Circadian Rhythms and Sleep in Space

Principal Investigator: Timothy H. Monk, Ph.D.

The specific aim of this experiment was to evaluate sleep, mood and activation, body temperature, and performance in crewmembers during long-duration space flight.

B. Sleep and Vestibular Adaptation

Principal Investigator: J. Allan Hobson, M.D.

The objectives of this study were to look at variations in sleep and dreaming over an extended period of space flight, with special attention to changes in sleep and dreaming associated with the vestibular adaptation that occurs with transition to and from microgravity conditions.

C. Microgravity, Sleep/Wake Immune Functions (SWIF) in Humans

Principal Investigator: Harvey Moldofsky, M.D.

This study assessed changes in the immune system coincident with sleep physiology during extended space flight and related any changes to preflight and postflight conditions. In particular, researchers wanted to determine if there are any long-term adverse effects of microgravity on the immune system that can be related to the sleep-wake cycle. Such disturbances in neuroendocrine system and immune system functions might have an impact on the risk for ill health, especially infectious disease.

Shuttle-Mir Missions

Mir-23/NASA-4, Mir-24/NASA-5

Approach

During NASA-4/Mir-23, three crewmembers completed measurements relating to the combined sleep protocol. The experiment was divided into three 12-day segments called measurement "blocks" spread throughout the mission. During each of the three 12-day blocks (early, middle, and late mission), the crewmembers completed pre- and postsleep questionnaires, measured body temperature (orally) 5 times per day, completed mood and activation tests (5 per day), and completed a performance test (1 per day). Dr. Monk's research team used this information to test the hypothesis that space flight causes changes in the CTS resulting in bouts of sleep disruption and impairments in daytime mood, alertness and functioning.

Also on each of the three 12-day blocks, crewmembers monitored sleep by wearing an apparatus called a Night Headband Monitor (NHM). The NHM was specifically designed to measure the various stages of sleep by recording brain wave activity, eye movement and head movement. The headband was connected to a computer and all data stored on disk. Dr. Hobson's research team used the data to determine the quantity and quality of sleep, especially REM sleep, in the test subjects.

On days 4 and 5 of the second and third blocks, crewmembers attached electrodes and wore a Medilog Sleep Research Recorder (MSRR) skull cap prior to sleep. This piece of hardware was used to assess the relationship of brain waves during sleep to immune functions. Blood samples were also drawn on days 4 and 5 of the second and third blocks. The samples were collectd in the early afternoon (approximately 2 PM) and prior to sleep. Dr. Moldofsky's team used the blood samples to measure blood immune parameters. After flight, the blood analyses and MSRR data were compared to test that changes in sleep, particularly between wakefulness and sleep, are indices of causal mechanisms that produce changes in immune parameters.

This investigation was conducted for the first time during the NASA-4/Mir-23 mission. The experiment protocols were repeated on NASA-5/Mir-24 mission with two additional crewmembers.

Results

One astronaut and four cosmonauts wore the Night Headband Monitor for a total of 317 nights of sleep data. Subjects recorded an average of 26 nights of sleep during the preflight period, 24 nights in flight, and 14 nights during the postflight recovery period. All told, 120 nights of sleep data were collected in flight, between the 24th and 171st day in orbit. Sixty of the 120 nights were recorded more than three months into the flight.

Preliminary analyses showed that REM sleep was severly diminished during flight for all five subjects. Both REM time and REM % (of total sleep time) were significantly diminished. On average, REM time was greatly reduced in flight compared to preflight. In contrast, postflight rates were essentially the same as preflight, showing on average a slight increase in REM time as compared to the preflight period. There was also a decrease in total sleep time in flight. All subjects showed decreases in average nightly total sleep time. This did not result from a decrease in time in bed; subjects spent on average 4% longer in bed while in flight. Rather, it resulted from a decreased sleep efficiency.

Preflight, inflight and postflight subjects answered questions on sleepiness, fatigue, pain and mood as well as performance that had been incorporated into a battery of questions. Detrimental effects were observed in alertness, mood and preceived work performance on the day following sleep episodes of five hours duration or less.

Immunologic and endocrine assays were carried out on the blood samples collected preflight, in flight, and postflight. The relationship between sleep activity to immune functions was examined. The preflight baseline data collection from all crewmembers were compared to a group of healthy male volunteers to determine if sleep/wake age-related immune and endocrine functions were present in the middle-aged male crewmembers during baseline conditions before flight on Mir versus young healthy males.

Middle-aged crewmembers in preflight baseline conditions differed from young healthy males in the timing of the diurnal pattern of NK cytotoxicity, hGH and cortisol. They also secreted less hGH and more cortisol over a 24-hour period. These hypothalamic-pituitary-adrenocortical (HPA) axis endocrine differences in healthy middle-aged men were similar to those seen in healthy older men. While the dynamic structure of NK cytotoicity differed, there was no overall mean difference from young males.

The Night Headband Monitor (NHM) permitted more extensive sleep recording during space flight than has been previously possible. The data collected over 6 months of flight indicated that extended space flight leads to a consistent and pronounced decrease in sleep eficiency, time spent in REM sleep, and the percent total sleep time spent in REM sleep as measured by the NHM. Neither the causes nor the consequences of these alterations are clear, but the continued reduction in these values might well lead to diminished performance of crewmembers in space.

Earth Benefits

Night workers and people who travel rapidly across time zones run into problems that arise from their circadian systems. Sleep is often interrupted or shortened and daytime mood, alertness and performance impaired. Study of sleep, circadian rhythms, and performance in space allows us to understand what happens to people when they are removed from most of the time cues on Earth. Findings from Dr. Monk's experiment will thus help us to understand the actions of time cues on the human circadian system, and will help us in providing useful coping strategies to night workers and those suffering from jet-lag. His findinges will also be useful in determining what happens to sleep, circadian rhythms and performance when individuals have to respond to major events, be they expected (e.g. extra crew onboard) or unexpected (e.g. a fire). Dr. Hobson's experiment will provide the most extensive recording of sleep over prolonged exposure to microgravity yet obtained and the first collection of dream reports from space. This research will provide additional insight to the effects of sleep posture on the quality and quantity of sleep and even dreaming. Dr. Moldofsky's experiment has significant implications not only for the success, safety, and productivity of space missions, but also on the health and well-being of astronauts. Findings from the experiment will help researchers understand the actions of time cues on the human circadian system, and will help doctors provide useful coping strategies for astronauts and others who experience disturbances in the circadian timing system.

Publications

Monk TH, Buysse DJ, and Rose LR. Wrist actigraphic measures of sleep in space. J Sleep (in press).

Monk TH, Buysse DJ, Billy BD, Kennedy KS, Willrich LM. Sleep and circadian rhythms in four orbiting astronauts. J Biol Rhythms;1998(13)3:188-201.

Leslie, K.R., Stickgold, R.A., DiZio, P., Lackner, J., and Hobson, J.A. ''Sleep and vestibular adaptation: Implications for function in microgravity.'' J. Vestib. Res., vol. 8, no. 1, 81-94 (1998).

Principal Investigators

Timothy H. Monk, Ph.D.

University of Pittsburgh

J. Allan Hobson, M.D.

Harvard University Medical School

Harvey Moldofsky, M.D.

University of Toronto, Canada

Irina Ponomareva

Institute of Biomedical Problems

Co-Investigators

Irina Larina, M.D.

Kathy S. Kennedy, B.A.

Bart D. Billy, M.S.

Timothy Hoffman, M.S.T.

Lynda R. Rose

Linda M. Willrich, B.S.

Franklin A. Lue, M.S.E.E.

A.W. MacLean, Ph.D.

R.M. Gorczynski, Ph.D., M.D.

James MacFarlane, Ph.D.

C.G. Jiang, M.D.

Robert Strickgold, Ph.D.