Sleep, performance, circadian rhythms, and light-dark cycles during two space shuttle flights

Area of Science:

• Space Medicine
• Chronobiology
• Neuroscience

Background:

• Astronauts face unique challenges to sleep and circadian regulation in space.
• Spaceflight alters light-dark cycles and rest-activity patterns, impacting physiological rhythms.

Purpose of the Study:

• To investigate the effects of space missions on astronaut sleep, circadian rhythms, and neurobehavioral performance.
• To assess the impact of altered light-dark and rest-activity cycles on astronaut health.

Main Methods:

• Collected sleep, circadian rhythm, and neurobehavioral data from astronauts before, during, and after space missions.
• Utilized questionnaires, actigraphy, and polysomnography for sleep assessment.
• Monitored body temperature and urinary cortisol rhythms.

Main Results:

• Space missions led to shorter rest-activity cycles and variable light-dark exposure.
• Reduced amplitude of body temperature rhythm and misaligned cortisol rhythm were observed.
• Astronauts exhibited decreased neurobehavioral performance, reduced sleep duration (approx. 6.5 h/day), and diminished sleep quality.
• Polysomnography showed increased wakefulness and less slow-wave sleep.
• Melatonin administration did not improve sleep; REM sleep increased post-flight.

Conclusions:

• Spaceflight significantly disrupts astronaut circadian rhythms and sleep patterns.
• These disruptions result in impaired neurobehavioral performance and altered sleep architecture.
• Post-flight REM sleep increase suggests a rebound effect from sleep deprivation during the mission.