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Physiological effects of light on the human circadian pacemakerThe physiology of the human circadian pacemaker and its influence and on the daily organization of sleep, endocrine and behavioral processes is an emerging interest in science and medicine. Understanding the development, organization and fundamental properties underlying the circadian timing system may provide insight for the application of circadian principles to the practice of clinical medicine, both diagnostically (interpretation of certain clinical tests are dependent on time of day) and therapeutically (certain pharmacological responses vary with the time of day). The light-dark cycle is the most powerful external influence acting upon the human circadian pacemaker. It has been shown that timed exposure to light can both synchronize and reset the phase of the circadian pacemaker in a predictable manner. The emergence of detectable circadian rhythmicity in the neonatal period is under investigation (as described elsewhere in this issue). Therefore, the pattern of light exposure provided in the neonatal intensive care setting has implications. One recent study identified differences in both amount of sleep time and weight gain in infants maintained in a neonatal intensive care environment that controlled the light-dark cycle. Unfortunately, neither circadian phase nor the time of day has been considered in most clinical investigations. Further studies with knowledge of principles characterizing the human circadian timing system, which governs a wide array of physiological processes, are required to integrate these findings with the practice of clinical medicine.
Document ID
Document Type
Reprint (Version printed in journal)
Shanahan, T. L.
(Brigham and Women's Hospital, Harvard Medical School Boston, MA 20115, United States)
Czeisler, C. A.
Date Acquired
August 22, 2013
Publication Date
August 1, 2000
Publication Information
Publication: Seminars in perinatology
Volume: 24
Issue: 4
ISSN: 0146-0005
Subject Category
Aerospace Medicine
Funding Number(s)
Distribution Limits
Review, Tutorial
Non-NASA Center
NASA Discipline Regulatory Physiology
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