Development of Circadian Sleep-Wake Rhythms in Preterm and Full-Term Infants

Abstract

ABSTRACT. We have compared the roles of neurologic maturity and environmental time cues in the development of the entrained circadian sleep-wake rhythm in the preterm and term human infant. The preterm infants (n = 19) spent some time after birth in a hospital nursery with no environmental time cues, whereas the term infants (n = 22) were exposed from birth to a cyclical light and dark environment with one major caregiver. The circadian sleepwake rhythm in the preterm infants entrained after a similar time of exposure to an environment with daily time cues but at an earlier postconceptional age when compared with the term group. We conclude, therefore, that it is the length of exposure to environmental time cues, rather than neurologic maturity, that determines the entrainment of the circadian rhythm of sleep and wakefulness in the human infant. (Pediarr Res 29: 381-384, 1991) The daily sleep-wake cycle in the adult is a circadian rhythm, i.e. it is a behavioral rhythm that is generated by an endogenous biologic clock and in the absence of external time cues it "freeruns" with a periodicity of approximately 25 h (1). Normally, however, the circadian sleep-wake pattern is entrained or synchronized to an exact 24-h period by external time cues that are known as zeitgebers. It has been proposed that the light-dark cycle and also social cues act as zeitgebers on the endogenous circadian pacemaker to synchronize the human sleep-wake cycle to a 24-h period ( 1 ).Although there is extensive literature that documents that sleep is consolidated toward the night by the 6th to 14th wk of life (2-6), there have been few attempts to define the factors that determine the timing of entrainment of the infant's circadian sleep-wake rhythm to the day-night cycle. It has been widely accepted that the emergence of an entrained circadian sleepwake pattern in the human infant is predominantly the result of maturation of the CNS (2-6). This is supported by the demonstration using spectral analysis that sleep-wake activity has a more prominent 24-h component in term infants when compared with preterm infants at the same postnatal age (7-13 wk),-.It may be misleading, however, to compare the development of circadian sleep-wake rhythms in pre-and full-term infants without taking into account the differences in the range of zeitgebers that these infants are exposed to after birth. A fullterm infant born at home or in hospital, where "rooming-in" with the mother is the normal practice, is exposed to a cyclical light-dark environment and the circadian behavioral and social patterns of a single caregiver. In contrast, the preterm infant will spend some time after birth in a hospital neonatal nursery where there is constant illumination and where there are several different caregivers in any 24-h period (8). Any difference between term and preterm infants in the timing of the development of an entrained circadian sleep-wake pattern may therefore not only be due to differences in maturity but also to exposure to a different range of zeitgeb...

Influence of light exposure during early life on the age of onset of bipolar disorder

“…Second, human preterm infants were able to entrain the circadian clock by exposure to low-intensity cycled lighting (Rivkees, 2003;Rivkees et al, 2004). When comparing term and preterm infant circadian entrainment, the length of exposure to a cyclical light-dark environment was more important than neurologic maturity (McMillen et al, 1991). Third, the timing of the association found in this study, over the first 3 months of life, is consistent with prior reports of the progressive development of the circadian system in humans.…”

Circadian and Sleep Development in Preterm Infants Occurs Independently From the Influences of Environmental Lighting

“…In support of our data, McMillen et al (23) also found the circadian rhythm of sleep in the preterm infants similar to term infants entrained after 6 to 10 wk of exposure to the home environment. However, because preterm infants were discharged home at approximately 35 wk PCA in their study, the entrainment to light-dark cycle took place at a significantly earlier PCA (47 wk) in these infants compared with the term group (49 wk).…”

Salivary cortisol as a tool for physiological studies and diagnostic strategies

“…The onset of the circadian rhythm of sleep was detected from 8 postnatal weeks in this preterm group. This age is similar to those previously reported for preterm (9.8 ± 2 weeks) and term (8.7 ± 2.7 weeks) babies (8). There was a parallelism between the appearance of such rhythm and the mean age at the onset of the salivary cortisol circadian rhythm.…”

“…In addition, this in-formation is not available for premature infants. The ontogenetic maturation of the circadian sleep-wake rhythms in preterm and full-term infants has been widely accepted as the result of the length of exposure to environmental time cues, rather than neurologic maturity (7)(8)(9). These observations prompted us to compare the effects of prematurity on the temporal evolution of the circadian variation in salivary cortisol and on the daily rhythm of sleep and wakefulness in preterm infants.…”