Nonnutritive Sucking and Response Thersholds in Young Infants

The motor response to tickling of 24 4-day-old healthy neonates was tested during ordinary restful sleep, when the infants were sucking on a pacifier in sleep, and during sleep when they had a pacifier in their mouth but were not sucking. The results indicate that sucking renders the sleeping infant unresponsive to an external stimulus. A similar but less marked rise in response thresholds was observed when a pacifier was in the baby's mouth but the baby was not sucking. In this condition, the infant usually responded to the stimulus with a new burst of sucking rather than a burst of difuse motility, as in ordinary sleep. Various interpretations for these findings are considered.