Ultra-Short Light Pulses as Efficient Countermeasures for Circadian Misalignment and Objective Performance and Subjective Alertness Decrements

Lighting protocols have been recognized by NSBRI (National Space Biomedical Research Institute), NASA, and NIH (National Institutes of Health) as important countermeasures for circadian rhythm and sleep disruptions and their associated effects on performance and alertness for both crews in space and workers on Earth. The current light-based countermeasures involve one or more hours of bright light exposure. We have recently demonstrated significant circadian phase shifting with an ultra-short 2-minute bright light stimulus. The use of such a short duration stimulus as a countermeasure would significantly preserve the ability to work in the International Space Station (ISS) lighting environment and reduce crew resource requirements. We proposed to test the relative efficacy of both ultra-short and longer-duration light protocol countermeasures using the newly approved ISS lighting system to induce both adaptive circadian resetting and direct alerting effects. Experiments were conducted jointly with Dr. S. Lockley and his NSBRI project "The ISS Dynamic Lighting Schedule: An in-flight lighting countermeasure to facilitate circadian adaptation, improve sleep and enhance alertness and performance on the International Space Station." These studies will further our understanding of the physiologic mechanisms that mediate exposure-duration-dependent and wavelength-dependent effects of photic stimuli on circadian phase and performance. Furthermore, results from these experiments will be added to our validated physiologically-based mathematical models of light, sleep/wake and circadian rhythms effects on performance and alertness, including a software application used for determining the optimal timing of light exposure to be employed as a countermeasure for predicted times of poor performance and alertness. The experimental and modeling results will have direct Earth-based applications for workers on early-rising, night, or rotating schedules, as well as for people experiencing jet lag. The work directly addresses one of the NSBRI NASA Research Announcement (NRA) research objectives and two NASA Human Research Program Integrated Research Plan (IRP) Risks. This proposal will also address other NSBRI goals: training of future scientists, collaboration among NSBRI investigators, and a combination of basic science with space-based applications and potential commercial applications.

NOTE: Follow-on continues as a directed research project as "Ultra-Short Light Pulses as Efficient Countermeasures for Circadian Misalignment and Objective Performance and Subjective Alertness Decrements--HFP00006."

Light is the major environmental time cue that resets the circadian pacemaker in the the mammalian hypothalamus. Light information is captured exclusively by the eyes using specialized cells containing a blue-light sensitive photopigment. Each day the light-dark cycle resets the internal clock, which in turn synchronizes the physiology, psychology, and behavior controlled by the clock. Failure to receive this light-dark information, as experienced for example by totally blind individuals, causes the circadian pacemaker to revert to its endogenous non-24-hour period and possibly become desynchronized from the 24-hour light-dark cycle. Exposure to irregular light-dark cycles, as experienced for example by psychiatric patients with irregular sleep-wake cycles, can also disrupt circadian rhythms. Light also suppresses the hormone melatonin and has a direct arousal effect on the brain, improving alertness and performance. This property of light can be useful as a non-pharmacological treatment for fatigue in a number of conditions, and if timed appropriately, these effects can complement the circadian phase resetting effects of light, for example in treating shiftwork and jet-lag disorders, to help maintain alertness at the correct time and subsequently improve sleep. The results of our experiments in which gradual vs. slam-shift changes in schedule along with continuous or intermittent light exposure are tested for their effects on circadian rhythms, sleep, hormones, subjective alertness, and objective performance will be applicable to conditions such as jet lag, and shift-work or night-work. Millions of workers in the safety, security, transportation, healthcare, and industrial sectors are affected by these conditions yearly, with effects on health and safety.

The development of (i) mathematical models of circadian rhythms, sleep, alertness, and performance, and (ii) software based on these models to facilitate schedule design, can improve performance and alertness and thereby effectiveness and public safety for people who work at night, on rotating schedules, on non-24-hr schedules, or on extended duty schedules (e.g., pilots, train and truck drivers, shift workers, healthcare workers, public safety officers). Attempting to sleep at adverse circadian phases is difficult, resulting in poor sleep efficiency. Similarly, attempting to work at adverse circadian phases, and/or after a long time awake, results in poor worker performance and productivity and leads to an increase in errors. For example, the accidents at the Chernobyl and Three Mile Island nuclear reactors and the Exxon Valdez grounding were all partially attributed to employees working at adverse circadian phases and the FAA (Federal Aviation Administration) reports of air traffic controllers sleeping while scheduled to work at night are related to their work schedule. The mathematical models and the available software that implements these models can be used to simulate and quantitatively evaluate different work and light exposure schedules to predict the expected circadian phase, subjective alertness, and performance in an individual.

Our software has been requested by members of NASA, academia, government, and industry, including airline, safety, medical, and military applications. Its use could help produce improved work schedules for both astronauts and ground-crew. The mathematical modeling efforts and software have also been used in educational programs and in the popular press to teach students and teachers about circadian rhythms and sleep and their effects on alertness and performance. NIRS monitoring may be useful in identifying individuals who might be at increased risk of sleep-related errors and occupational injuries. The cost-effective and minimally intrusive NIRS (Near Infrared Spectroscopy) assessment of regional brain activity may be applicable in personnel in safety-sensitive occupations, for better understanding the physiology underlying attentional failures, and for developing countermeasures for these failures.

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