Bright light affects human circadian rhythms
- 536 Downloads
The relative effectiveness of external zeitgebers synchronizing circadian rhythms can be evaluated by mesuring the size of the range of entrainment. The experimental approach to measure entrainment limits is the application of an artificial zeitgeber with slowly and steadily changing period. In human circadian rhythms, an absolute light-dark (LD) cycle with a light intensity during L of 100 lux or less, results in an upper entrainment limit of 26.91±0.24 hours. The same limit is reached in constant illumination when only informations are given to the subjects. Consequently, the LD cycle is effective mainly with its behavioral component characterized by the request of the light-dark alternation to go to rest. In experiments with the same experimental protocol but higher intensity of illumination during L (∼400 lux, i.e., exceeding the threshold beyond which melatonin excretion is suppressed in humans), human circadian rhythms can be synchronized within a much larger range; the upper entrainment limit is, with all overt rhythms measured, beyond 29 hours. This means that bright light has an effect on the human circadian system which is qualitatively different from that of dim light, and which is similar to the effect of light in most animal experiments. This finding has theoretical and practical implications.
Key wordsHuman circadian rhythms Limits of entrainment Bright light effects Melatonin threshold
Unable to display preview. Download preview PDF.
- Czeisler, C.A., Richardson, G.S., Zimmerman, J.C., Moore-Ede, M.C., Weitzman, E.D. (1981): Entrainment of human circadian rhythms by light-dark cycles: a reassessment. Photochem. Photobiol. 34:239–247.Google Scholar
- Lewy, A.J., Wehr, T.A., Goodwin, F.K., Newsome, D.A., Markey, S.P. (1980): Light suppresses melatonin secretion in humans. Science 210: 1267–1269.Google Scholar
- Menaker, M., Takahashi, J.S., Eskin, A. (1978): The physiology of circadian pacemakers. Ann. Rev. Physiol. 40: 501–526.Google Scholar
- Wever, R. (1969): Autonome circadiane Periodik des Menschen unter dem Einfluss verschiedener Beleuchtungs-Bedingungen. Pflügers Arch. 306: 71–91.Google Scholar
- Wever, R. (1970): Zur Zeitgeber-Stärke eines Licht-Dunkel-Wechsels für die circadiane Periodik des Menschen. Pflügers Arch. 321: 133–142.Google Scholar
- Wever, R.A. (1979): The Circadian System of Man. Springer-Verlag, New York-Heidelberg-Berlin.Google Scholar
- Wever, R.A. (1982a): Behavioral aspects of circadian rhythmicity. In: Rhythmic Aspects of Behavior (F.M. Brown and R.C. Graeber, eds.), pp. 105–171. L. Erlbaum Ass. Inc., Hillsdale N.J.Google Scholar
- Wever, R.A. (1982b): Organization of the human circadian system: internal interactions. In: Circadian Rhythms in Psychiatry (F.K. Goodwin and T.A. Wehr, eds.). Boxwood Press, Neurosciences Series, Los Angeles Cal. (in press).Google Scholar
- Wever, R.A. (1983): Fractional desynchronization of human circadian rhythms: a method for evaluating entrainment limits and functional interdependencies. Pflügers Arch. (in press).Google Scholar