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Circadian Rhythms in the Martian Environment

Principal Investigator:
Charles A. Fuller, Ph.D.

University of California, Davis

Human physiology and behavior are precisely regulated to the Earth’s light intensity, day length and gravitational pull. Astronauts can be adversely affected by space’s dissimilar environment. Dr. Charles A. Fuller is examining primates’ circadian responses under exposure to the simulated light spectrum and day length of Mars, and in altered gravity. He will also determine whether timed light pulses will help the primates adapt to the Martian environment.

NASA Taskbook Entry

Technical Summary

To maintain health and homeostasis, an organism must regulate each of its physiological systems in concert with all of the others and with the external environment. The Circadian Timing System (CTS) has evolved to allow coordination of an organism's physiology and behavior both internally and with the external 24-hour (h) terrestrial day. The mammalian CTS is adapted to the lighting environment found on Earth. As we move toward exploration-class space missions, we will be exposing astronauts to non-Earth environments for increasing lengths of time. Changes may include altered gravity and spectral, intensity and day-length differences. This raises the concern of whether or not humans will be able to synchronize to such an alien environment. For example, a Mars-type exploration would entail stays on Mars of one to two years.

Compared with the Earth, the Martian environment has a photic spectrum shifted to the red, low illumination level, a periodicity of 24.62-h, and a 0.38-g gravitational field. The mammalian CTS is most sensitive to light of the blue-green wavelengths and adapted to synchronize to a 24.0 hr day. In addition, light must be relatively bright to affect the CTS of primates, especially humans. Further, altered CTS function - including rhythm amplitude and wave form, sensitivity to light and CTS period - have been reported in both the microgravity environment of space flight and in hyperdynamic fields on the Earth. This program will examine the ability of primates (male and female rhesus monkeys) CTS to cope with the Martian environment.

The first three experiments will examine responses to the Martian day, while the last experiment will examine the effects of gravity on the period of the circadian pacemaker. Experiment 1 will examine the ability of the CTS to synchronize to the Martian photic (spectrum and period) environment. We will examine long-term (four month) physiological and behavioral responses. Experiment 2 will similarly examine long-term responses to a photic environment composed of a Martian day and Earth-light spectrum. Experiment 3 will use the primate model to initiate the development of countermeasures to assure optimum entrainment of the CTS. This experiment will examine the effects of timed, bright-light pulses on CTS entrainment.

Using the forced desynchrony protocol, Experiment 4 will examine the effects of one-, one and a half- and two-g on the period of the circadian pacemaker. We will develop a G vs. period model to predict the effect of the 0.38-g Martian environment on the period of the circadian pacemaker. This model will be used to develop countermeasure requirements to be tested in Experiment 3. Thus, this program will develop a primate model to evaluate physiological and behavioral consequences of long-term exposure of male and female subjects to altered lighting and gravitational environments.

This project's funding ended in 2004