Fetuses and neonates have different heart rate responses to low-intensity stimulation in quiet sleep

A sustained heart rate (HR) deceleration, elicited by low-intensity stimula tion, is considered part of Sokolov's generalized orienting reflex and is a useful measure of information processing in nonverbal subjects, This study was undertaken to investigate developmental changes in the perinatal perio d in information processing during quiet sleep (QS). Twenty-six infants wer e tested as fetuses at 36-40 weeks and again as neonates at a postnatal age of 2 weeks. Quiet sleep was defined in the same way for fetuses and neonat es, and the same airborne sound was used for fetal and neonatal testing. We found that stimulation elicited a sustained, monophasic HR deceleration in the majority of fetuses. However, the response was more heterogenous when these infants were tested after birth, with approximately half the 2-week-o ld infants exhibiting a prolonged HR deceleration and half exhibiting a HR acceleration. These data provide evidence that a developmental change may o ccur, between the prenatal and postnatal periods, in information processing during QS. (C) 2000 Elsevier Science Inc. All rights reserved.