Neonatal Startles, Smiles, Erections, and Reflex Sucks as Related to State, Sex, and Individuality

Frequencies of startles, reflex smiles, erections, and reflex sucks were recorded in the context of the state in which they occurred in 32, 2- to 3-dayold healthy neonates. States were monitored for each infant during 2 hours and 20 minutes divided in 6 observation periods. Observer agreements ranged from 80 percent to 100 percent on the infants' states and from 93 to 100 percent on the spontaneous behaviors. Results confirm Wolff's findings (1966) that there is a highly significant relation between state and the type and frequency of the spontaneous behaviors. The frequencies are highest during regular sleep when the infant is most deafferented and they diminish in direct proportion to the infant's closeness to wakefulness. Results on sex differences reflect a consistent trend that males startle more in all states and females engage more frequently in reflex smiles and bursts of rhythmical mouthing. Since the mean rate of the spontaneous behaviors is almost identical for males and females when erections are excluded, it appears that females make up in smiles and reflex sucks what they lack in startles. The data also suggest that erections are spontaneous behaviors which occur over and above the other discharge behaviors. Rank correlations showed that individual infants tend to rely heavily on specific discharge channels over states (e.g., .77 for erections, .53 for rhythmical mouthing). The discussion focuses on the possible function of the spontaneous behaviors for providing endogenous afferent stimulation under conditions of deafferentation, during a period when such stimulation may be critical for the developing central nervous system, and on the potential significance of these behaviors for later development.