Infants' brain responses to pupillary changes in others are affected by race

Infants' salivary oxytocin and positive affective reactions to people

Oxytocin is a neuropeptide positively associated with prosociality in adults. Here, we studied whether infants' salivary oxytocin can be reliably measured, is developmentally stable, and is linked to social behavior. We longitudinally collected saliva from 62 U.S. infants (44 % female, 56 % Hispanic/Latino, 24 % Black, 18 % non-Hispanic White, 11 % multiracial) at 4, 8, and 14 months of age and offline-video-coded the valence of their facial affect in response to a video of a smiling woman. We also captured infants' affective reactions in terms of excitement/joyfulness during a live, structured interaction with a singing woman in the Early Social Communication Scales at 14 months. We detected stable individual differences in infants' oxytocin levels over time (over minutes and months) and in infants' positive affect over months and across contexts (video-based and in live interactions). We detected no statistically significant changes in oxytocin levels between 4 and 8 months but found an increase from 8 to 14 months. Infants with higher oxytocin levels showed more positive facial affect to a smiling person video at 4 months; however, this association disappeared at 8 months, and reversed at 14 months (i.e., higher oxytocin was associated with less positive facial affect). Infant salivary oxytocin may be a reliable physiological measure of individual differences related to socio-emotional development.

A novel(ty) perspective of fear bias

Grossmann presents an exciting and interesting theory on the function of fearfulness. In this commentary it is argued that fearfulness may be a byproduct of a larger executive functioning network and these early regulatory skills considered more broadly may be key building blocks for later cooperative behaviors.

Examining the Role of Socioeconomic Status and Maternal Sensitivity in Predicting Functional Brain Network Connectivity in 5-Month-Old Infants

Infancy is a sensitive period of human brain development that is plastically shaped by environmental factors. Both proximal factors, such as sensitive parenting, and distal factors, such as socioeconomic status (SES), are known predictors of individual differences in structural and functional brain systems across the lifespan, yet it is unclear how these familial and contextual factors work together to shape functional brain development during infancy, particularly during the first months of life. In the current study, we examined pre-registered hypotheses regarding the interplay between these factors to assess how maternal sensitivity, within the broader context of socioeconomic variation, relates to the development of functional connectivity in long-range cortical brain networks. Specifically, we measured resting-state functional connectivity in three cortical brain networks (fronto-parietal network, default mode network, homologous-interhemispheric connectivity) using functional near-infrared spectroscopy (fNIRS), and examined the associations between maternal sensitivity, SES, and functional connectivity in a sample of 5-month-old infants and their mothers (N = 50 dyads). Results showed that all three networks were detectable during a passive viewing task, and that maternal sensitivity was positively associated with functional connectivity in the default mode network, such that infants with more sensitive mothers exhibited enhanced functional connectivity in this network. Contrary to hypotheses, we did not observe any associations of SES with functional connectivity in the brain networks assessed in this study. This suggests that at 5 months of age, maternal sensitivity is an important proximal environmental factor associated with individual differences in functional connectivity in a long-range cortical brain network implicated in a host of emotional and social-cognitive brain processes.

Processing third-party social interactions in the human infant brain

The understanding of developing social brain functions during infancy relies on research that has focused on studying how infants engage in first-person social interactions or view individual agents and their actions. Behavioral research suggests that observing and learning from third-party social interactions plays a foundational role in early social and moral development. However, the brain systems involved in observing third-party social interactions during infancy are unknown. The current study tested the hypothesis that brain systems in prefrontal and temporal cortex, previously identified in adults and children, begin to specialize in third-party social interaction processing during infancy. Infants (N = 62), ranging from 6 to 13 months in age, had their brain responses measured using functional near-infrared spectroscopy (fNIRS) while viewing third-party social interactions and two control conditions, infants viewing two individual actions and infants viewing inverted social interactions. The results show that infants preferentially engage brain regions localized within the dorsomedial prefrontal cortex when viewing third-party social interactions. These findings suggest that brain systems processing third-party social interaction begin to develop early in human ontogeny and may thus play a foundational role in supporting the interpretation of and learning from social interactions.

Individual differences in pupil dilation to others' emotional and neutral eyes with varying pupil sizes

Sensitivity to others' emotional signals is an important factor for social interaction. While many studies of emotional reactivity focus on facial emotional expressions, signals such as pupil dilation which can indicate arousal, may also affect observers. For example, observers' pupils dilate when viewing someone with dilated pupils, so-called pupillary contagion. Yet it is unclear how pupil size and emotional expression interact as signals. Further, examining individual differences in emotional reactivity to others can shed light on its mechanisms and potential outcomes. In the current study, adults' (N = 453) pupil size was assessed while they viewed images of the eye region of individuals varying in emotional expression (neutral, happy, sad, fearful, angry) and pupil size (large, medium, small). Participants showed pupillary contagion regardless of the emotional expression. Individual differences in demographics (gender, age, socioeconomic status) and psychosocial factors (anxiety, depression, sleep problems) were also examined, yet the only factor related to pupillary contagion was socioeconomic status, with higher socioeconomic status predicting less pupillary contagion for emotionally-neutral stimuli. The results suggest that while pupillary contagion is a robust phenomenon, it can vary meaningfully across individuals.

Variability in Infants' Functional Brain Network Connectivity Is Associated With Differences in Affect and Behavior

Variability in functional brain network connectivity has been linked to individual differences in cognitive, affective, and behavioral traits in adults. However, little is known about the developmental origins of such brain-behavior correlations. The current study examined functional brain network connectivity and its link to behavioral temperament in typically developing newborn and 1-month-old infants (M [age] = 25 days; N = 75) using functional near-infrared spectroscopy (fNIRS). Specifically, we measured long-range connectivity between cortical regions approximating fronto-parietal, default mode, and homologous-interhemispheric networks. Our results show that connectivity in these functional brain networks varies across infants and maps onto individual differences in behavioral temperament. Specifically, connectivity in the fronto-parietal network was positively associated with regulation and orienting behaviors, whereas connectivity in the default mode network showed the opposite effect on these behaviors. Our analysis also revealed a significant positive association between the homologous-interhemispheric network and infants' negative affect. The current results suggest that variability in long-range intra-hemispheric and cross-hemispheric functional connectivity between frontal, parietal, and temporal cortex is associated with individual differences in affect and behavior. These findings shed new light on the brain origins of individual differences in early-emerging behavioral traits and thus represent a viable novel approach for investigating developmental trajectories in typical and atypical neurodevelopment.

Probing infants' sensitivity to pupil size when viewing eyes

Sensitive responding to eye cues plays a key role in human social interactions. Pupil size provides subtle cues regarding a social interaction partner's arousal states. The current study assessed infants' sensitivity to and preference for differences in pupil size. Specifically, we examined White 14-month-old infants' pupillary responses when viewing own-race and other-race (Asian) eyes with dilating, constricting, and static medium-sized pupils. Our results show that, independent of race, infants' pupils dilated more when viewing eyes with dynamically changing (dilating and constricting) pupils than when viewing eyes with non-changing, static, and medium-sized pupils. We also measured infants' looking preferences, showing that, independent of race, infants preferentially attended to eyes with dilated pupils. Moreover, our results show that infants orient more quickly to pupillary changes in own-race eyes than in other-race eyes. These findings demonstrate that infants detect, but do not mimic, changes in pupil size in others and show a preference for eyes with dilated pupils.

Gut microbiota composition is associated with newborn functional brain connectivity and behavioral temperament

The gut microbiome appears to play an important role in human health and disease. However, only little is known about how variability in the gut microbiome contributes to individual differences during early and sensitive stages of brain and behavioral development. The current study examined the link between gut microbiome, brain, and behavior in newborn infants (N = 63; M [age] = 25 days). Infant gut microbiome diversity was measured from stool samples using metagenomic sequencing, infant functional brain network connectivity was assessed using a resting state functional near infrared spectroscopy (rs-fNIRS) procedure, and infant behavioral temperament was assessed using parental report. Our results show that gut microbiota composition is linked to individual variability in brain network connectivity, which in turn mediated individual differences in behavioral temperament, specifically negative emotionality, among infants. Furthermore, virulence factors, possibly indexing pathogenic activity, were associated with differences in brain network connectivity linked to negative emotionality. These findings provide novel insights into the early developmental origins of the gut microbiome-brain axis and its association with variability in important behavioral traits. This suggests that the gut microbiome is an important biological factor to consider when studying human development and health.

Pupil mimicry in infants and parents

Changes in pupil size can reflect social interest or affect, and tend to get mimicked by observers during eye contact. Pupil mimicry has recently been observed in young infants, whereas it is unknown whether the extent and the speed of infants' pupil mimicry response are identical to that of adults. Moreover, the question of whether pupil mimicry in infants is modulated by the race of the observed other remains to be explored. In two studies, pupil mimicry was investigated in infants and their parents. In the first study, 6-, 12- and 18-month-olds (n = 194) and their parents (n = 192) observed eyes with dynamically dilating, constricting, or static pupils. Infants mimicked the pupil sizes of the observed eyes like their parents, but responded slower. Study 2 replicated these findings in a new sample of infants (n = 55, 12-month-olds) and parents (n = 64), and further showed that the pupil mimicry response was not significantly modulated by the race of the observed partner neither in infants nor in parents. We conclude that pupil mimicry is an ancient bonding mechanism that helps to connect people.

fNIRS for Tracking Brain Development in the Context of Global Health Projects

Over the past 25 years, functional near-infrared spectroscopy (fNIRS) has emerged as a valuable tool to study brain function, and it is in younger participants where it has found, arguably, its most successful application. Thanks to its infant-friendly features, the technology has helped shape research in the neurocognitive development field by contributing to our understanding of the neural underpinnings of sensory perception and socio-cognitive skills. Furthermore, it has provided avenues of exploration for markers of compromised brain development. Advances in fNIRS instrumentation and methods have enabled the next step in the evolution of its applications including the investigation of the effects of complex and interacting socio-economic and environmental adversities on brain development. To do this, it is necessary to take fNIRS out of well-resourced research labs (the majority located in high-income countries) to study at-risk populations in resource-poor settings in low- and middle-income countries (LMICs). Here we review the use of this technology in global health studies, we discuss the implementation of fNIRS studies in LMICs with a particular emphasis on the Brain Imaging for Global Health (BRIGHT) project, and we consider its potential in this emerging field.