Light Treatment for Sleep Disorders: Consensus Report. II. Basic Properties of Circadian Physiology and Sleep Regulation

Abstract The rationale for the treatment of sleep disorders by scheduled exposure to bright light in seasonal affective disorder, jet lag, shift work, delayed sleep phase syndrome, and the elderly is, in part, based on a conceptual framework developed by nonclinical circadian rhythm researchers working with humans and other species. Some of the behavioral and physiological data that contributed to these concepts are reviewed, and some pitfalls related to their application to bright light treatment of sleep disorders are discussed. In humans and other mammals the daily light-dark (LD) cycle is a major synchronizer responsible for entrainment of circadian rhythms to the 24-h day, and phase response curves (PRCs) to light have been obtained. In humans, phase delays can be induced by light exposure scheduled before the minimum of the endogenous circadian rhythm of core body temperature (CBT), whereas phase advances are induced when light exposure is scheduled after the minimum of CBT. Since in healthy young subjects the minimum of CBT is located approximately 1 to 2 h before the habitual time of awakening, the most sensitive phase of the PRC to light coincide