Sex differences in newborns with special reference to differences in the organization of oral behavior

Sex Differences in the Development of a Separate Sense of Self During Infancy: Directions for Future Research

Women have been characterized as having more difficulty than men in developing a separate sense of self. This sex difference is held to have its origins in infancy in the differential response of mothers to sons and daughters. While there is clinical evidence for this sex difference, as yet there is no clear support for it in the experimental literature. In this paper we provide a foundation for future experimental research on the origins in mother-infant interaction of sex differences in the development of a separate sense of self. Using Mahler's description of the separation-individuation process as a general framework, we specify behavioral indicators of differential progress in the development of a separate sense of self at each subphase of separation-individuation and define the particular maternal behaviors relevant to that progress. An examination of existing experimental studies that employ these measures suggests that sex differences in the experience of a separate sense of self begin to emerge in early infancy and that mothers engage in different types of contact with sons and daughters in ways that facilitate the achievement of separation more for boys than for girls. The implications of these findings for future research are discussed.

Sex Differences in Response to Marijuana in a Social Setting

Due to the failure to include women in the subject samples of most experimental investigations of the effects of cannabis, the possibility exists that the data obtained on this social intoxicant are applicable to only 49% of the population. Those few studies that have compared males and females have focused on performance variables and have demonstrated very few differences. It was hypothesized that the most likely area for male/female marijuana differences would be that of social interactions and behaviors related to these interactions.

In a relaxed, informal atmosphere, Es videotaped the social interactions of groups of female friends, female strangers, male friends, or male strangers as they smoked coltsfoot, placebo, and marijuana. In addition to social-condition and drug-condition differences, we obtained statistically significant effects indicating that the women responded both to the social situations and to the drug differently from the men. In general, the women interacted with each other more positively than did the men. These effects were paralleled by sex differences in mood, person perception, and even in how pleasurable or annoying the experimental tasks were.

These data are of import not only in the area of cannabis research but in the field of social interactions and the study of female/male differences as well.

Sex differences in newborn interaction with mother or father during skin-to-skin contact after Caesarean section

AIM

To investigate differences between the breast-seeking and crying behaviour of girls and boys in skin-to-skin contact (SSC) with their mother or their father after Caesarean section as well as the point-in-time for the first breastfeeding and to compare mothers' and fathers' interactive behaviour with their newborn girl or boy.

METHODS

Twenty girls and 17 boys were randomized to 25 min of SSC with one or the other parent immediately after birth. The interaction was videotaped.

RESULTS

Girls started rooting movements earlier than boys in SSC with either parent (p = 0.027). Infants started to breastfeed significantly earlier if having been in SSC with mothers compared with SSC with fathers during the first 5-30 min (p = 0.018). Girls cried more than boys in SSC with either parent (p = 0.02). Mothers used more touching behaviour towards their newborn infant than fathers (p = 0.001). Mothers touched girls less than boys (p = 0.038). Fathers directed less speech towards girls compared with boys (p = 0.042).

CONCLUSION

Early mother-infant SSC immediately after Caesarean section should be promoted until the occurrence of the first breastfeed. If the mother is unable to provide SSC immediately after birth, the father-infant SSC is a valuable alternative because it enhances paternal interaction.

Sexing the baby: Part 1--What do we really know about sex differentiation in the first three years of life?

The most common paradigm used to analyze health differences between men and women, is to divide the body from the social environment. In such a model, the bodily contribution and the social contribution add up to 100%. A few health science researchers offer more sophisticated approaches. None, however, offer an intensive study of the first several years of life in order to offer a model which integrates biology and culture in a fashion that demonstrates the productive processes by which gender itself emerges. In this article, we identify the earliest known sex-related biological and behavioral differences in young infants, toddlers and their parents and indicate how these might relate to health and disease. We frame these differences using unifying concepts from the study of neuroplasticity and dynamic systems theory.

Behavioral gender differences in the neonatal period according to the Brazelton scale

The aim of the present study was to analyze gender differences in neonatal behavior. A sample of 188 healthy full-term newborns (88 boys and 100 girls) was assessed. The behavioral evaluations were performed using the Brazelton Neonatal Behavioral Assessment Scale (NBAS), when the infants were between 48 and 80 hours old. Girls had higher scores than boys in 4 out of the 34 behavioral items of the NBAS. These are the following: Orientation Animate Auditory (t=2.486; P=0.014), Alertness (t=2.546; P=0.012), Quality of Alertness (t=3.091; P=0.002), and State Regulation (t=2,343; P=0.020). Boys had higher scores in the Irritability item (t=-2.186; P=0.030). We have analyzed also the possible effects of the medication during delivery because mothers of boys were more likely to have used this medication but no differences have been found among the mentioned items. These results appear to confirm that similarities between boys and girls are much more the norm than differences related to gender, but even though they are quite subtle, differences do exist in the way newborn infants react and behave in the neonatal period.

Sex differences in neonates' cuddliness

The authors undertook the present study to determine whether under ecologically valid, low-stress conditions, female and male neonates could be differentiated on cuddliness. Sixteen female and 15 male neonates were videotaped interacting briefly with both a female and a male adult who were blind to the sex of the neonate. Raters coded degree of cuddliness and activity level. Results showed that raters could discriminate the sex of the neonate on the basis of degree of cuddliness. Discussion focuses on the importance of theoretical and methodological considerations in assessing sex differences in behavioral characteristics of neonates.

Evidence of sex-specific differences in masticatory jaw movement patterns

The complexity of human oral functional movements has not been studied in detail quantitatively, and only recently have studies begun to evaluate whether such movements contain sex-specific characteristics. Therefore, the purposes of this study were: (1) to quantify in detail the jaw movements and associated masticatory electromyographic activity occurring during gum chewing, and (2) to explore these data for evidence of sex specificity. Fourteen male and 17 female subjects participated in the study. Approximately 11 right- and 11 left-sided chewing cycles and associated masticatory electromyographic activity were sampled from each subject. The samples were quantified into 165 variables per chewing cycle, averaged to create a single multivariate vector for each subject, and then analyzed by a step-wise discriminant analysis. With a combination of 6 variables, a jackknifed cross-validation test found the probability of correct classification to be 93.5%. These findings support the hypothesis that masticatory jaw movements contain sex-specific features.

Shock of birth. Evaluation of neurologic status of term newborn in the first 48 hours of life

The shock of birth is a transient depression of muscle tone and deep tendon reflexes seen in newborn babies shortly after birth. We evaluated the shock of birth in a sample of 313 consecutive term newborns at 4, 24 and 48 hours of life. We correlated neurologic findings on examination with maternal, obstetric and perinatal data. Special attention was given to the relationship between the mode of delivery and shock of birth. Of the maternal data, factors associated with the shock of birth were obstetric gestational age, previous gestations, abortion or previous vaginal deliveries. Presence of stained amniotic fluid at birth was associated with the shock of birth. There was also a correlation between shock of birth and newborn sex, birth weight, thoracic circumference and the Battaglia and Lubchenco classification. The shock of birth lasted less than 24 hours in 70% of the newborns and less than 48 hours in 84.3%. We conclude that the mode of delivery, vaginal or cesarean section, did not influence the shock of birth. We also established the duration and factors associated with this phenomenon.

Hemispheric specialization in infant chimpanzees (Pan troglodytes): evidence for a relation with gender and arousal

The current study extends previous documentation of behavioral asymmetries in hand-to-mouth, self-consoling behaviors of infant chimpanzees. The underlying source of lateralized hand-to-mouth, self-calming behavior was investigated by comparing individual differences in neonatal arousal levels, regulatory ability, and motor performance with individual differences in the degree of laterality at 3 months. Asymmetrical hand-to-mouth, self-calming behaviors at 3 months of age were significantly related to general arousal at 2 days of age (i.e., the Range of State cluster scores measured by the Brazelton Neonatal Behavioral Assessment Scale). Simply stated, chimpanzees with a right-hand bias in hand-to-mouth behavior exhibited lower arousal at 2 days of age compared with nonright-handed individuals. The only item of the Range of State cluster to distinguish subjects was irritability: Right-handed subjects were less irritable. Previously, a trend was reported with respect to sex differences in the laterality of hand-to-mouth behavior. With the greater number of subjects in the present study, we found that females exhibited a significantly greater right-hand bias for hand-to-mouth behaviors (12 of 13) than did males (9 of 15). We conclude that neonatal arousability, and not regulatory capacity or motor performance, predicts the degree of laterality found in hand-to-mouth, self-calming behaviors in 3-month-old chimpanzees. These data are discussed from the standpoint of early pari-parturitional or intrauterine factors affecting lateralized development.

The analysis of sucking behaviour in newborn infants

A special video camera devised by the author and a fiberscope were used to film the neonatal sucking response of 50 low-risk full-term newborn infants on the 5th day after birth. Analysis of the sucking behaviour showed that the sucking movements consist mainly of a peristaltic tongue movement and two kinds of negative pressure; that the peristaltic tongue movements are synchronized with the jaw movements; that infants actively adapt to a varying environment; and that the sucking movements change to minimize the energy required.

Pain expression in neonates: facial action and cry

Pain expression in neonates instigated by heel-lance for blood sampling purposes was systematically described using measures of facial expression and cry and compared across sleep/waking states and sex. From gate-control theory it was hypothesized that pain behavior would vary with the ongoing functional state of the infant, rather than solely reflecting tissue insult. Awake-alert but inactive infants responded with the most facial activity, consistent with current views that infants in this state are most receptive to environmental stimulation. Infants in quiet sleep showed the least facial reaction and the longest latency to cry. Fundamental frequency of cry was not related to sleep/waking state. This suggested that findings from the cry literature on qualities of pain cry as a reflection of nervous system 'stress', in unwell newborns, do not generalize directly to healthy infants as a function of state. Sex differences were apparent in speed of response, with boys showing shorter time to cry and to display facial action following heel-lance. The findings of facial action variation across sleep/waking state were interpreted as indicating that the biological and behavioral context of pain events affects behavioral expression, even at the earliest time developmentally, before the opportunity for learned response patterns occurs. Issues raised by the study include the importance of using measurement techniques which are independent of preconceived categories of affective response.

Implications of sex differences in neonatal temperament for early risk and developmental/environmental interactions

Sex differences in neonatal temperament were examined in 30 pairs of full-term, opposite-sex twins. Behavior was assessed during feeding, during sleep, while awake for orienting responses, in response to a stressor, and for measures of spontaneous irritability and soothability. Composite and summary scales described irritability, resistance to soothing, reactivity, reinforcement value of the infant's behavior, activity during sleep, and activity while awake. Analyses of variance of paired comparisons performed separately for each behavioral area indicated that female neonates were more irritable and more difficult to soothe than male neonates. The results are discussed in terms of maturational effects on neonatal behavior, implications for infant-caregiver interaction, and their relation to environmental influences on development.

Mother-infant interaction; effects of sex of infant on feeding behaviour

Mother--child interaction was studied on the 2nd and 4th days after delivery. Mothers with girls showed more distal contact behaviour such as talking, smiling, and 'en face' responses. They also displayed more skin-to-skin contact behaviour (patting, rubbing, kissing, and touching) toward girl babies. Mothers with boys, on the other hand, showed more types of behaviours directed to clothed parts of the infant such as patting and adjusting clothes. These findings were statistically significant only on the 2nd day after delivery. On day 4 differences between male and female infants both in the frequency and in the pattern of sucking were observed.

Early behavioral differences: gender or circumcision?

In human studies, the possible long-term effects on behavior of early physical insult or pharmacological agents have received little attention. We present both circumstantial and direct evidence that circumcision of male infants leads to behavioral changes. In some American studies using circumcised infants, reported gender differences may instead be the result of the altered behavior of circumcised males. We suggest that circumcision requires more study in its own right, and that it requires description if not control in all neonatal and infancy studies.