Biological Cycles Affect Development of Fetuses, Infants

By Henderson, Zorika Petic | Human Ecology Forum, Spring 1995 | Go to article overview

Biological Cycles Affect Development of Fetuses, Infants


Henderson, Zorika Petic, Human Ecology Forum


Research on fetal and infant behavior leads to a better understanding of the complexities of early human development. This knowledge is the basis for future advances in the identification, prevention, and treatment of developmental disorders.

Sometimes infants will stare at a person with such intensity, it's as though they're spellbound. Then in a blink they'll lose all interest.

No insult is intended. They're likely being prodded into exploring and interacting with the rest of the world by bursts of activity within their central nervous system. These bursts, which have irregular cycles, may play an important role in neural and mental development.

"Most living systems have cycles that govern their behavior," says Steven S. Robertson, associate professor of human development and family studies. "If humans and other animals didn't have circadian cycles built into their systems, for example, they'd be thrown for a loop each time the sun rose or set. They wouldn't be anticipating or preparing for what was about to happen.

"Within the longer cycles of sleep and wakefulness, there are shorter cycles, both regular and irregular. The significance of some of these shorter cycles, such as breathing and cardiac cycles, are obvious. The importance of other cycles that are less than 24 hours has been a mystery for a long time. But we're starting to get clues that some of them may affect an organism's ability to process information from the environment."

In research on the human fetus and infant, Robertson has discovered that bursts of activity followed by rest occur every one to four minutes.

Studies Robertson did on six-week- and twelve-week-old infants revealed that a surge in motor activity ended their intense visual concentration.

As part of the studies, infants were allowed to look as long as they liked at brightly colored pictures or stuffed animals. Their body movements were monitored through sensor pads placed beneath them, and their visual exploration of the interesting sights was monitored by videotapes of their eye movements.

"The videotapes showed that visual attention is more likely to be disengaged when motor activity is increasing or accelerating," Robertson says. "This may lead infants to explore the complex visual world that surrounds them by interrupting their long fixations on a single object.

"It is also possible that in some infants these otherwise beneficial interruptions are too frequent and disruptive. This may, in fact, be the developmental origin of some types of attention disorders."

The same cycles of motor activity followed by pauses were found by Robertson in several studies of human fetuses between 25 and 41 weeks of gestation.

Such cycles are known to be affected by the mother's medical status, but to what extent isn't clear. Robertson conducted a study of diabetic mothers in their third trimester of pregnancy to find out if the cycles were adversely affected.

Poorly controlled diabetes can have serious consequences for the fetus and infant, including neurological problems and excessive growth, and Robertson suspected that it would also influence the patterns of motor activity. The study showed that cycles of motor activity were temporarily absent in 55 percent of the fetuses, compared to 10 percent of fetuses of nondiabetic mothers. The absence of cycles was most pronounced in the mothers whose diabetes was least well controlled.

In a second study, Robertson found that fetal behavior was sensitive to short-term (30 to 60 minutes) fluctuations in the mothers' blood sugar levels, By the end of gestation, however, the cycles of motor activity appeared normal. A follow-up study after birth confirmed that the newborn infants, who as fetuses had been exposed to an abnormal metabolic environment, showed normal patterns of spontaneous activity.

"Whatever mechanisms are responsible for the cyclic fluctuations in activity seem to be buffered from any lasting effects of the mother's diabetes," Robertson observes. …

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