Entrainment of a free-running human with bright light?
The case of a 40-year-old sighted woman with free-running sleep-wake and melatonin rhythms is presented. The subject was studied for 102 days. During the pre-treatment period, both the sleep-wake and melatonin rhythms had a period of 25.1 hr, similar to the average period of humans living in temporal isolation. Treatment consisted of bright artificial light exposure (2500 lx Vita-Lite) for 2 hr each day upon awakening. Clock time of light exposure was held constant for 6 days and then slowly advanced until the subject was arising at her desired time of day. The subject continued the light treatment at home and was able to live on a 24-hr day for the 30-day follow-up study. While other factors may be operating in this situation, it is possible that the light treatment caused the stabilization of the free-running rhythms, advancement to a normal phase and entrainment to the 24-hr day. We suspect that the tendency to free-run was related to sleep onsets that were abnormally delayed relative to the circadian phase response curve for light. By scheduling a 2-hr pulse of bright light each morning, this tendency to delay would be counteracted by light-induced advances, resulting in normal entrainment.
Hoban
T M
TM
Department of Psychiatry, Oregon Health Sciences University, Portland 97201.
Sack
R L
RL
Lewy
A J
AJ
Miller
L S
LS
Singer
C M
CM
D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology / Q000528:radiation effects*; D005260:Female; D006801:Humans; D008027:Light; D008550:Melatonin / Q000097:blood; D010789:Phototherapy; D012890:Sleep / Q000502:physiology / Q000528:radiation effects
D008550:Melatonin