LIGHT TREATMENT FOR SLEEP DISORDERS - CONSENSUS REPORT .4. SLEEP PHASE AND DURATION DISTURBANCES

Advanced and delayed sleep phase disorders, and the hypersomnia that c an accompany winter depression, have been treated successfully by appr opriately timed artificial bright light exposure. Under entrainment to the 24-h day-night cycle, the sleep-wake pattern may assume various p hase relationships to the circadian pacemaker, as indexed, for example , by abnormally long or short intervals between the onset of melatonin production or the core body temperature minimum and wake-up time. Adv anced and delayed sleep phase syndromes and non-24-h sleep-wake syndro me have been variously ascribed to abnormal intrinsic circadian period icity, deficiency of the entrainment mechanism, or-most simply-pattern s of daily light exposure insufficient for adequate phase resetting. T he timing of sleep is influenced by underlying circadian phase, but ps ychosocial constraints also play a major role. Exposure to light early or late in the subjective night has been used therapeutically to prod uce corrective phase delays or advances, respectively, in both the sle ep pattern and circadian rhythms. Supplemental light exposure in fall and winter can reduce the hypersomnia of winter depression, although t he therapeutic effect may be less dependent on timing.