"Taken together, these findings raise an interesting possibility," said Frick. "In infancy, cortisol responses may be less dependent on hard-wired biological rhythms and more influenced by the HPA axis activity of the baby's immediate caregivers."
The team conducted the research using 32 baby-mother pairs. Nineteen of the babies were female and 13 were males, and they ranged in age from 7.8 to 17.4 months. After agreeing to participate, mothers were instructed to collect saliva samples using cotton swabs from inside the mouths of their infants and then themselves four times on a single day: when the infants awoke in the morning, 30-45 minutes after the baby awoke, when the baby awoke from its first nap of the day and 30-45 minutes after that. Other requirements applied, but they weren't difficult for the mothers to follow, said Bright.
No one knows at precisely what age the CAR begins in humans, though it had previously been predicted to be present sometime in the first year. The current data indicates that it emerges at a much older age, however. Why babies don't emit rising amounts of cortisol in response to awakening isn't clear, either.
"It is possible that the CAR is absent or more difficult to detect in early childhood because of the developmental stage of the hippocampus and related structures," said Bright.
Understanding how the CAR develops in infants could offer clues as to how adults respond to such things as stress in later life. Other scientists have found, for instance, that women who as infants or children were subjected to maltreatment and inconsistency of care showed higher than normal levels of cortisol on
|Contact: Melissa Bright|
University of Georgia