1997/01/07 by Scott A. Rivkees, Paul L. Hofman, Jeffrey D Fortman · 2 citations
Medicine · Neuroscience · #Biology #Circadian clock #Circadian rhythm #Circadian rhythm and melatonin #Endocrinology #Entrainment (biomusicology) #Evolutionary biology #Internal medicine #Light Cycle #Light effects on circadian rhythm #Light intensity #Medicine #Neuroscience #Non human primate #Optics #Photoreceptor and optogenetics research #Physiology #Primate #Rhythm #Sleep and Wakefulness Research #Suprachiasmatic nucleus
paper · doi:10.1073/pnas.94.1.292
openalex publication_date 1997/01/07 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/25
At the present time we do not know when the circadian timing system of human infants becomes responsive to light. Because of human study limitations, it is not currently possible to address this issue in clinical studies. Therefore, to provide insights into when the circadian system of humans becomes responsive to light, baboons were studied. We first assessed if the biological clock located in suprachiasmatic nuclei (SCN) is responsive to light at birth. When term newborn infants were exposed to bright light at night (5000 lux), SCN metabolic activity and c-fos mRNA expression increased, indicating the presence of photic responsiveness. When photic entrainment of developing rhythmicity was examined in infants, low intensity (200 lux) cycled lighting was sufficient to entrain circadian phase. However, low intensity lighting was not sufficient to induce changes in SCN metabolic activity or c-fos mRNA expression. Phase-response studies indicated that light exposure (200 lux) before the onset of activity most effectively shifted circadian phase. These data provide direct evidence that the SCN are responsive to visually mediated light information in a primate at birth. Further consideration of lighting conditions that infants are exposed to is therefore warranted.