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Overview

Mathematical Model for Scheduled Light Exposure: Circadian/Performance Countermeasure

Principal Investigator:
Megan E. Jewett, Ph.D.

Organization:
Harvard - Brigham and Women's Hospital

Effective human performance is dependent on the body’s synchronization of its circadian rhythm with the work schedule. This synchronization is thrown off by the space environment, but carefully scheduled light exposures can realign astronauts’ circadian rhythms to match their sleep-wake schedules. Dr. Megan E. Jewett is developing a mathematical model to predict circadian rhythms under various lighting conditions. This model will then be formatted into a computer program that can help determine appropriate lighting schedules for astronauts on extended missions and for people who do shift work or travel across time zones.

NASA Taskbook Entry

Technical Summary

The Original Aims of our Project:
  • Specific Aim 1: To further develop and refine our 'Dynamic Stimulus Processing' Light Model so that it can accurately predict the phase and amplitude of the human circadian system under any lighting conditions, especially those that occur in space. This will be done using data from four completed studies of the effects on the human circadian system of: i) three-cycles of brief bright light pulses; ii) three-cycles of extended bright light pulses; iii) three-cycles of extended low- and moderate-intensity light pulses; and iv) single- and double-cycles of amplitude-suppressing critically-timed extended bright light pulses.
     
  • Specific Aim 2: To validate the Light Model refined above in Specific Aim 1 using data from four other completed studies of the effects on the human circadian system of: v) single-cycle patterns of brief bright light pulses; vi) single-cycle extended bright light pulses; vii) single-cycle extended light pulses across a wide range of intensities; and viii) sleep-wake/light-dark schedules with a wide range of periods (11-h, 20-h, 23.5-h, 24-h, 24.6-h, 28-h, 42.85-h), different light intensities during wake (1, 8, or 15 lux), and with or without a single exposure to an extended bright light stimulus (in the 11-h condition only).
     
  • Specific Aim 3: To incorporate the Light Model refined and validated above in Specific Aims 1 and 2 into our mathematical Neurobehavioral Performance Model, which will then be validated against experimental performance data collected under the wide variety of lighting conditions encompassed in the eight studies described above in Specific Aims 1 and 2.
     
  • Specific Aim 4: To develop a user-friendly Circadian Performance Simulation Software (CPSS) package that can be used to specify appropriate light schedules as a countermeasure to the poor performance and sleep quality associated with circadian misalignment in space.
The Key Findings of the Project:
  1. We refined and validated our current circadian pacemaker model to predict the effects of different stimuli on entrainment and phase resetting of pacemaker at low light levels.
     
  2. We characterized the amplitude recovery dynamics of the endogenous pacemaker as well as identified different excitation regions of the pacemaker.
     
  3. Our user-friendly Circadian Performance Simulation Software (CPSS) package was tested with actual mission schedule to evaluate our predictions of performance and alertness during pre and post-launch conditions.
     
  4. A preliminary algorithm for schedule assessment and countermeasure design was developed based on the analysis of different schedules using CPSS.

The Impact of these Findings:

  1. The impact of finding 1 above suggests that the circadian pacemaker can be entrained using different stimuli and the current mathematical model can be used for simulating the effect of flight on pacemaker dynamics during long duration space missions.
     
  2. The impact of finding 2 above suggests the rate of recovery from amplitude reduction is slower and therefore returns to equilibrium conditions may take longer. This has implications for the rate of recovery after disruption of the pacemaker (e.g. by different shift schedules or lighting conditions). Amplitude reduction of the pacemaker may affect the influence of circadian pacemaker on sleep consilidation or neurobehavioral performance during the daytime.
     
  3. The impact of finding 3 is that there is now available a software package to evaluate our predictions of the performance and alertness of crewmembers during long-duration space missions
     
  4. The impact of finding 4 is that the algorithm can be incorporated into our software package to assess the schedules of long duration space missions in order to design appropriate countermeasures to improve the performance and alertness of crewmembers on these missions.

 

Earth Applications

This research focuses on the further development of mathematical models and software that aid in schedule design to improve performance (and thereby public safety) for people who work at night, on rotating schedules or on non-24-hour schedules (pilots, train and truck drivers, shift workers, health care workers, etc.). This research also aids in the specification of lighting requirements aboard spacecraft and in other work conditions to insure proper entrainment and circadian phase of these workers, even if they work at night or on rotating schedules.
This project's funding ended in 2004