Symposium
Chair: Elliott M. Blass
This symposium draws on research on the integration of biologicalstate, changes in the central nervous system, maturation, and specificclasses of experience. We will identify how these factors determine human,rat, and rhesus monkey infants state and motor characteristics atparticular times during development, and how they contribute tocharacteristics as diverse as: induction of analgesia, learning aboutparticular sounds, development of face recognition, and social reciprocitybetween infants and familiar adults, especially mothers. The genetic andneurochemical changes underlying some of these characteristics will beidentified and discussed as will future directions in developmentalresearch that take into consideration new genetic and neuroimaging advancesthat can be used to further understanding of traditional developmentalissues.
Details of individual items:
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In efforts to identify the contribution of different facets of thenursing-suckling interaction on stress and pain relief, previous studieshave demonstrated analgesias induced by different forms of gustatorystimulation and by nonnutritive suckling in rat and human infants. Thepresent report places stress reduction and analgesia within the largercontext of the mother holding her infant in skin-to-skin contact. When soheld, newborns essentially do not cry during an otherwise painful heelstick procedure, nor do they emit facial gestures that normally signifypain. Heart rate is not increased suggesting stress relief as well asanalgesia. Thus, all three domains of mother-infant interactions conferanalgesia in both rats and humans. Moreover, all three classes arerewarding in rats, and support learning about some of her specificfeatures. Because the mechanisms underlying suckling and its consequencesare remarkably well preserved, we determined whether certain facets of thesuckling act would support learning about and preferring particular faces.We will demonstrate that 9- and 12-week - old infants learn about andprefer a face to which they had been exposed for only 3-min. if they hadreceived either sucrose, alone or on a pacifier, during eye-to-eye contact.The bases of face recognition, affective change and face preference will bediscussed.
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Variance in biobehavioral traits is always the product of both genetic andenviornmental factors -- and their interactions, and the relative influence ofthese factors can change throughout development. We assessed the relativecontribution of such factors on measures of orientation, motor maturity,activity, and state control in 322 laboratory-born rhesus monkey neonatesbelonging to a single pedigree throughout their first month of life, using astandardized Brazelton-like neonatal examination administered on Days 14 and 30of life. Heritability was estimated using variance components methods, in whichregression was employed to simultaneously estimate the effects of sex andrearing condition (mother- vs. nursery-rearing). Significant heritability wasdemonstrated for the state control, orientation, and activity, but not the motormaturity, clusters on Day 14. These heritability patterns changed with age, suchthat the state control and orientation heritabilities increased, the activitycluster heritability decreased, and the motor maturity cluster value remainedrelatively stable from 14 to 30 days of age. Significant effects of rearingcondition were found for all four clusters at both ages, except for Day 30 motormaturity scores; significant sex differences were detected for Day 30 activity(males higher) and motor maturity (females higher) clusters only. A second setof analyses involving 115 of these rhesus monkey neonates used associationtechniques to compare infants homozygous for the long variant of the serotonintransporter gene regulatory region polymorphism (5-HTTLPR) or heterozygous forthe long and short form of the allele. Significant influences of genotype andrearing condition were demonstrated for orientation, state control, andactivity, but not for motor maturity cluster scores. Importantly, specificgene-environment interactions were demonstrated for the first 3 clusters, suchthat the genotypic effects were generally more pronounced in the nursery-rearedthan in the mother-reared infants, and these differences became more dramaticwith increasing age.
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Objective and Design. Prototypical components of infant caretaking include provision of nutrients and contact. Here we investigate a potential role of nutrients on infant memory. We conducted a controlled trial of glucose effects on memory for repeated auditory word stimuli in 50 2-3 day old human newborns. Infants were randomized to receive a 2 gm/kg 20% (w/v)glucose, or water, feed 20 minutes prior to an infant controlled information processing procedure consisting of Orientation--Habituation, Delay (100 seconds), Spontaneous Recovery and Novelty phases. Per cent of trials with head turns (>45 degrees for 3 sec.) toward a word stimulus ('tinder' or 'beagle') was the principle dependent measure. Number of trials to reach criteria for orientation was taken as a measure of attention; trials to reach criteria for habituation as a measure of rate of learning; and % trials with head turns toward during Spontaneous Recovery (following delay) as a measure of memory. Infants who did not remember the stimulus were expected to increase head turns towards the stimulus following the delay (that is, to treat the prior stimulus word as 'new' again) whereas infants who remembered the stimulus were expected not to. Per cent head turns toward a different word during Novelty was required to assure responsiveness and rule out neuronal fatigue.Results. Blood glucose determined following the procedure was significantly higher in infants receiving a glucose feed (Glucose vs Water: Mean +/- 1 SD; 6.3+/-0.9 vs 4.0+/-0.4 mmoles/L, t3D9.0; P<0.001). There was no difference in trials to orientation (4.1+/-1.6 vs 5.0+/-2.1, t3D1.7; P3D0.10) or trials to habituation (10.6+/-2.7 vs 11.0+/-3.3, t3D0.4; P3D0.69) implying similar attention to the stimuli and rates of learning in both groups. However, during SpontaneousRecovery, % trials with head turns toward were 31.8+/-27.4 % (similar to % head turns towards during habituation) for infants receiving glucose and 57.7+/-31.5% (similar to % head turns towards during orientation) for infants receiving water (t3D2.8; P<0.01). There was no difference in % head turns towards to a new word during Novelty (63.7+/-29.7 vs 71.0+/-25.2, t3D0.9; P3D0.40).Conclusions and Interpretation. The results imply that infants receiving glucose, but not infants receiving water, remembered the word stimulus following the 100 second delay. This difference was specific to memory for the stimulus, and not attributable to differences in attention to the stimulus, rate of learning or responsiveness to word stimuli following the delay. A meandifference of 2.3 mmoles/L in blood glucose concentration was sufficient to enhance memory, but whether it is the difference, absolute level, or rate of change in glucose that is required to enhance memory remains to be determined. Since levels of glucose achieved following a 2 gm/kg glucose feed overlap those following a standard milk feeding, typical infant feeding may enhance memory for auditory stimuli as part of everyday caregiving interaction.
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The cradle of emotional and social cognitive development is construed as the meeting of newborns' attentional predisposition toward faces and the uncontrollable propensity of caretakers to maintain infants manifestly happy. Based on a body of recent research, changes in the nature of early face-to-face exchanges in the course of the first 9 months are considered. Therole of mothers as conversational partners changes markedly at around 2 months with the emergence of socially elicited smiling. From this developmental transition, mothers start scaffolding the affective state of their infant beyond calming and interventions to suppress cry. While maintaining long bouts of eye-to-eye contacts, mothers typically provide repetitive and well defined protoconversational narratives (e.g., peek-a-boo, patty cake, 'I am going toget you' games) to their attentive infants. These narratives are used as dynamic scaffolds of infants' happy state, ultimate interactive devices to control infants' positive mood when in an alert and awake state. These narratives are also the objective means used by caretakers to establish and develop intersubjectivity with young infants: the primary sense of shared feelings and experience which is at the origin of social cognition. The mechanisms by which infants develop intersubjectivity in early face-to-face exchanges and within the context of well defined protoconversational narratives remain to a large extent unknown. Infancy researchers have tried for some years to provide evidence of an early, if not innate sensitivity to social contingency. From as young as 2 months of age, infants are sometimes shown to detect whether their mothers are timely responding to their own behavior. However, the early sensitivity to temporal contingency is not specific to the social domain, as infants from birth appear to detect the contingent consequences of their own action on inanimate objects. What is specific to the social domain is intersubjectivity and the sense of reciprocity with others. I shall argue that if it takes two to dance (e.g., mother and infant), it takes more than good timing to dance well. Based on a recent body of research, it appears that the development of a sense of reciprocity might well rest on the co-construction of protoconversational narratives between mothers and infants starting the second month of life, and not prior, as infants start unambiguously to smile in a social context. I present data suggesting that it is within this context that infants develop social expectations, selective affinities with strangers, and theories about the feelings of others in relation to their own.