Bye Bye Baby

Sleep and wake mechanisms of infants

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) There are many chemical factors at work in our bodies when we sleep and awaken. The hormone cortisol is a major factor that contributes to waking up.

For the first time, research has shown that this cortisol awakening response (CAR) is very different for infants than adults - in fact, it is the opposite.

"Babies wake up differently than adults."

Researchers at the University of Georgia studied the CAR effect in babies, something that hasn't been widely studied. Calling cortisol the "Swiss Army knife of hormones," the university's research report says that just when scientists think they understand what cortisol does, another function pops up.

In the infant study, 32 mother-baby pairs were used, with infants ranging in age from 7.8 to 17.4 months. Mothers collected saliva samples from their baby's mouth using a cotton swab four times a day: after waking in the morning, 30-45 minutes after awakening, after waking from the first nap of the day, and 30-45 minutes after that. The mothers also collected saliva samples from themselves.

Researchers observed that, unlike in adults, cortisol levels didn't increase for infants from the time they awoke or for half an hour afterward, in the morning or after naps. Melissa Bright, who led the study, concluded that the adult pattern of cortisol response isn't present at birth. Rather than increasing and decreasing the way it does in adults, cortisol levels remained stable in babies.

Interestingly, the study also revealed a mother-infant cortisol association called "psychological attunement," confirming recent research that cortisol levels between mothers and infants are correlated.

The findings could have implications for how infants handle stress and why proper care from their mothers could affect how growing children react to cortisol in later life.

Other research has found that women who as infants or children were subjected to maltreatment and inconsistency of care showed higher than normal levels of cortisol on awakening as adults.

"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.

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Review Date: 
December 6, 2011
Last Updated:
December 10, 2011