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Synchronization to a Non-24-Hour Day Reveals Flexibility within the Human Biological Clock

August 10, 2007

Boston, MA – Researchers from Brigham and Women’s Hospital’s (BWH) Division of Sleep Medicine successfully entrained, or synchronized, individuals to a light/dark cycle that correctly aligned their biological clock to the 24.65-hour day of the planet Mars and to the 23.5-hour day often experienced by astronauts flying in low orbit. Additionally, the entrainment to the Martian day resulted in long-term changes to the individuals’ circadian period of the biological clock, showing for the first time plasticity of, or flexibility within, this system in humans. These findings have important implications for human space exploration and circadian rhythm sleep disorders, and appear in the August 8, 2007 issue of Public Library of Science ONE.

Circadian rhythm sleep disorders – such as jet lag disorder, shift work disorder and advanced sleep phase disorder – are caused by misalignment between the biological clock and the rest/activity cycle. These can be caused by interindividual differences in circadian periods – a measure of how long it takes to complete one daily cycle.

“Understanding how our biological clock can be adjusted is a critical step in developing therapy for circadian rhythm sleep disorders, which disturb sleep at night and compromise daytime cognitive functioning,” said lead author Frank A. J. L. Scheer, PhD, associate director of the Medical Chronobiology Program at BWH.

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