The circadian time-keeping system is the neural system that allows predictive adaptation of
individuals to the reproducible 24-hour day/night alternations of our planet. A biological
clock, the suprachiasmatic nucleus, receives environmental information and imposes a
circadian pattern to physiological functions. Since the suprachiasmatic nucleus develops
early in gestation and circadian rhythms are present in the fetus and newborn, the circadian
system seems to be functional in fetal life and can receive circadian inputs through the …