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When children first meet a stranger, there is great variation in how much they will approach and engage with the stranger. While individual differences in this type of behavior-called social wariness-are well-documented in temperament research, surprisingly little attention has been paid to the social groups (such as race) of the stranger and how these characteristics might influence children's social wariness. In contrast, research on children's social bias and interracial friendships rarely examines individual differences in temperament and how temperament might influence cross-group interactions. The current study bridges the gap across these different fields of research by examining whether the racial group of an unfamiliar peer or adult moderates the association between temperament and the social wariness that children display. Utilizing a longitudinal dataset that collected multiple measurements of children's temperament and behaviors (including parent-reported shyness and social wariness toward unfamiliar adults and peers) across early childhood, we found that 2- to 7-year-old children with high parent-reported shyness showed greater social wariness toward a different-race stranger compared to a same-race stranger, whereas children with low parent-reported shyness did not. These results point to the importance of considering racial group membership in temperament research and the potential role that temperament might play in children's cross-race interactions. RESEARCH HIGHLIGHTS: Previous research on temperament has not considered how the race of strangers could influence children's social wariness. We find evidence that 2- to 7-year-old children with high parent-reported shyness show greater social wariness toward a different-race stranger compared to a same-race stranger. These results point to the importance of considering racial group membership in temperament research. Our findings also suggest temperament may play a role in children's cross-race interactions.

BackgroundPolicy debates over anti-poverty programs are often marked by pernicious stereotypes suggesting that direct cash transfers to people residing in poverty encourage health-risking behaviors such as smoking, drinking, and other substance use. Causal evidence on this issue is limited in the U.S. Given the prominent role of child allowances and other forms of cash assistance in the 2021 American Rescue Plan and proposed Build Back Better legislation, evidence on the extent to which a monthly unconditional cash gift changes substance use patterns among low-income mothers with infants warrants attention, particularly in the context of economic supports that can help improve early environments of children.MethodWe employ a multi-site, parallel-group, randomized control trial in which 1,000 low-income mothers in the U.S. with newborns were recruited from hospitals shortly after the infant's birth and randomly assigned to receive either a substantial ($333) or a nominal ($20) monthly cash gift during the early years of the infant's life. We estimate the effect of the unconditional cash transfer on self-report measures of maternal substance use (i.e., alcohol, cigarette, or opioid use) and household expenditures on alcohol and cigarettes after one year of cash gifts.ResultsThe cash gift difference of $313 per month had small and statistically nonsignificant impacts on group differences in maternal reports of substance use and household expenditures on alcohol or cigarettes. Effect sizes ranged between - 0.067 standard deviations and + 0.072 standard deviations. The estimated share of the $313 group difference spent on alcohol and tobacco was less than 1%.ConclusionsOur randomized control trial of monthly cash gifts to mothers with newborn infants finds that a cash gift difference of $313 per month did not significantly change maternal use of alcohol, cigarettes, or opioids or household expenditures on alcohol or cigarettes. Although the structure of our cash gifts differs somewhat from that of a government-provided child allowance, our null effect findings suggest that unconditional cash transfers aimed at families living in poverty are unlikely to induce large changes in substance use and expenditures by recipients.Trial registrationRegistered on Clinical Trials.gov NCT03593356 in July of 2018.

We have performed an investigation into the optical conductivity and magnetotransport properties of top-gated devices patterned on the topological insulator Bi2Se3 in order to determine the relative effects of the different carrier species that exist within these novel materials. We find that the topologically protected surfaces within our samples are partially screened from the action of the gate by trivial band-bending states formed at the top surface of the topological insulator. Despite this, the mobility of the topological surface carriers is significantly affected by the application of an external gate bias. Additionally, we find that the optical conductivity response is dominated by the topologically protected surface states, and that the optical conductivity is particularly sensitive to the scattering caused by the topological surfaces coupling to trivial states, arising from the bulk or band-bending induced surface states. These results will have interesting applications to the design of future plasmonic devices that incorporate topological materials.

Early childhood poverty is a risk factor for lower school achievement, reduced earnings, and poorer health, and has been associated with differences in brain structure and function. Whether poverty causes differences in neurodevelopment, or is merely associated with factors that cause such differences, remains unclear. Here, we report estimates of the causal impact of a poverty reduction intervention on brain activity in the first year of life. We draw data from a subsample of the Baby's First Years study, which recruited 1,000 diverse low-income mother-infant dyads. Shortly after giving birth, mothers were randomized to receive either a large or nominal monthly unconditional cash gift. Infant brain activity was assessed at approximately 1 y of age in the child's home, using resting electroencephalography (EEG; n = 435). We hypothesized that infants in the high-cash gift group would have greater EEG power in the mid- to high-frequency bands and reduced power in a low-frequency band compared with infants in the low-cash gift group. Indeed, infants in the high-cash gift group showed more power in high-frequency bands. Effect sizes were similar in magnitude to many scalable education interventions, although the significance of estimates varied with the analytic specification. In sum, using a rigorous randomized design, we provide evidence that giving monthly unconditional cash transfers to mothers experiencing poverty in the first year of their children's lives may change infant brain activity. Such changes reflect neuroplasticity and environmental adaptation and display a pattern that has been associated with the development of subsequent cognitive skills.

Childhood economic disadvantage is associated with lower cognitive and social-emotional skills, reduced educational attainment, and lower earnings in adulthood. Despite these robust correlations, it is unclear whether family income is the cause of differences observed between children growing up in poverty and their more fortunate peers or whether these differences are merely due to the many other aspects of family life that co-occur with poverty. Baby's First Years is the first randomized controlled trial in the United States designed to identify the causal impact of poverty reduction on children's early development. A total of 1000 low-income mothers of newborns were enrolled in the study and began receiving a monthly unconditional cash gift for the first several years of their children's lives. Mothers were randomly assigned to receive either a large monthly cash gift or a nominal monthly cash gift. All monthly gifts are administered via debit card and can be freely spent with no restrictions. Baby's First Years aims to answer whether poverty reduction in early childhood (1) improves children's developmental outcomes and promotes healthier brain functioning, and (2) improves family functioning and better enables parents to support child development. Here we present the rationale and design of the study as well as potential implications for science and policy.

Behavioral inhibition is a temperamental disposition to react warily when confronted by unfamiliar people, objects, or events. Behaviorally inhibited children are at greater risk of developing anxiety disorders later in life. Previous studies reported that individuals with a history of childhood behavioral inhibition exhibit abnormal activity in the hippocampus and amygdala. However, few studies have investigated the structural differences that may underlie these functional abnormalities. In this exploratory study, we evaluated rhesus monkeys exhibiting a phenotype consistent with human behavioral inhibition. We performed quantitative neuroanatomical analyses that cannot be performed in humans including estimates of the volume and neuron number of distinct hippocampal regions and amygdala nuclei in behaviorally inhibited and control rhesus monkeys. Behaviorally inhibited monkeys had larger volumes of the rostral third of the hippocampal field CA3, smaller volumes of the rostral third of CA2, and smaller volumes of the accessory basal nucleus of the amygdala. Furthermore, behaviorally inhibited monkeys had fewer neurons in the rostral third of CA2. These structural differences may contribute to the functional abnormalities in the hippocampus and amygdala of behaviorally inhibited individuals. These structural findings in monkeys are consistent with a reduced modulation of amygdala activity via prefrontal cortex projections to the accessory basal nucleus. Given the putative roles of the amygdala in affective processing, CA3 in associative learning and CA2 in social memory, increased amygdala and CA3 activity, and diminished CA2 structure and function, may be associated with increased social anxiety and the heritability of behavioral inhibition. The findings from this exploratory study compel follow-up investigations with larger sample sizes and additional analyses to provide greater insight and more definitive answers regarding the neurobiological bases of behavioral inhibition.

Motivation influences cognitive control, particularly in childhood and adolescence. Previous work finds that the error-related negativity (ERN), an event-related potential (ERP) linked to cognitive control following errors, is influenced by social motivation. However, it is unclear whether the influences of social motivation on the ERN extend to stimulus-locked neural correlates of cognitive control. This study reexamines how social motivation influences cognitive control in adolescence by exploring motivational influences on two stimulus-locked ERPs; the N2 and P3. Adolescent girls (8-17 years of age) completed a flanker task under two different conditions. In the social condition, girls were led to believe that they were evaluated by a peer during a flanker task. In the nonsocial condition, girls completed a flanker task while evaluated by a computer. Results revealed that all girls exhibited a larger P3 in social as compared to nonsocial contexts, whereas the N2 was not different between contexts. In addition, the largest P3 enhancements were observed among younger girls. These findings suggest that social motivation influences some ERP components related to cognitive control, and such influences change across development. Additionally, findings suggest the importance of including multiple ERPs when interpreting the functional significance of motivation on cognitive control.

Children at risk for anxiety display elevated threat sensitivity and may inaccurately classify safe stimuli as threatening, a process known as overgeneralization. Little is known about whether such overgeneralization might stem from altered sensory representations of stimuli resembling threat, especially in youth. Here we implement representational similarity analysis of fMRI data to examine the similarity of neural representations of threat versus ambiguous or safe stimuli in threat and perceptual neurocircuitry among children at varying levels of anxiety traits. Three weeks after completing threat conditioning and extinction, children underwent an fMRI extinction recall task, during which they viewed the extinguished threat cue (CS+), safety cue (CS-) and generalization stimuli (GS) consisting of CS-/CS+ blends. Multivoxel BOLD signal patterns were measured in seven regions of interest: four affective areas (ventromedial prefrontal cortex (vmPFC), anterior insular cortex (AIC), dorsomedial prefrontal cortex (dmPFC), and amygdala) and three perceptual areas (inferior temporal cortex (ITC) and visual areas V1 and V4). Compared to low anxious children, children with high trait anxiety evidenced less neural pattern differentiation between the CS+ and similar GS, particularly in the vmPFC. Together, these results demonstrate the utility of multivariate neuroimaging approaches in arbitrating the relative contributions of perceptual versus affective sources to threat generalization.

Theta oscillations (4-8 Hz) provide an organizing principle of cognitive control, allowing goal-directed behavior. In adults, theta power over medial-frontal cortex (MFC) underlies conflict/error monitoring, whereas theta connectivity between MFC and lateral-frontal regions reflects cognitive control recruitment. However, prior work has not separated theta responses that occur before and immediately after a motor response, nor explained how medial-lateral connectivity drives different kinds of control behaviors. Theta's role during adolescence, a developmental window characterized by a motivation-control mismatch also remains unclear. As social observation is known to influence motivation, this might be a particularly important context for studying adolescent theta dynamics. Here, adolescents performed a flanker task alone or under social observation. Focusing first on the nonsocial context, we parsed cognitive control into dissociable subprocesses, illustrating how theta indexes distinct components of cognitive control working together dynamically to produce goal-directed behavior. We separated theta power immediately before/after motor responses, identifying behavioral links to conflict monitoring and error monitoring, respectively. MFC connectivity was separated before/after responses and behaviorally-linked to reactive and proactive control, respectively. Finally, distinct forms of post-error control were dissociated, based on connectivity with rostral/caudal frontal cortex. Social observation was found to exclusively upregulate theta measures indexing post-response error monitoring and proactive control, as opposed to conflict monitoring and reactive control. Linking adolescent cognitive control to theta oscillations provides a bridge between non-invasive recordings in humans and mechanistic studies of neural oscillations in animal models; links to social observation provide insight into the motivation-control interactions that occur during adolescence.

Although many studies have examined the location and function of the mirror neuron system (MNS) in human adults, we know relatively little about its development. The current study fills this gap by using fMRI to examine for the first time the development of the brain regions implicated in action execution, action observation, and their overlap. We examined age-related differences in brain activation by contrasting a group of children (n = 21) and adults (n = 18). Surfaced-based analyses of action execution and action observation revealed that brain activity for action observation and execution in children is similar to adults, though adults displayed greater activity than children within the right superior parietal lobe during action execution and the occipital lobe during action observation compared to control. Further, within-individual measures of overlapping activation between action observation and execution revealed age-related differences, such that adults, compared to children, displayed more spatial overlap. Moreover, the extent of the overlap in activation across conditions was related to better motor skills and action representation abilities in children. These data indicate that the MNS changes between middle childhood and adulthood. The data also demonstrate the functional significance of the putative MNS to motor skills and action representation during development.

Adolescence is a developmental period characterized by increased social motivation and a heightened concern of peer evaluation. However, little research has examined social influences on neural functioning in adolescence. One psychophysiological measure of motivation, the error-related negativity (ERN), is an ERP following an error. In adults, the ERN is enhanced by contextual factors that influence motivation, such as social observation and evaluation. The current study examined relations among age and neural responses in social contexts in adolescence. Seventy-six adolescent girls (9-17 years old) completed a flanker task under two different conditions. In the social condition, adolescent girls were informed that two other adolescents would be observing and providing feedback about their performance. In the nonsocial condition, adolescent girls completed a flanker task alone and were told feedback was computer generated. Results revealed that younger adolescents exhibited a larger ERN in social contexts than nonsocial contexts. In contrast, there were no differences in the ERN between contexts among older adolescents. In addition, enhancements of the ERN in social contexts among younger adolescents diminished the relation between the ERN and age. These findings suggest that the ERN is sensitive to social contexts in early adolescence, and developmental changes in the ERN may be partially explained by contextual factors that influence motivation.

ObjectiveBehavioral inhibition (BI) is a temperament identified in early childhood that is a risk factor for later social anxiety. However, mechanisms underlying the development of social anxiety remain unclear. To better understand the emergence of social anxiety, longitudinal studies investigating changes at behavioral neural levels are needed.MethodBI was assessed in the laboratory at 2 and 3 years of age (N = 268). Children returned at 12 years, and an electroencephalogram was recorded while children performed a flanker task under 2 conditions: once while believing they were being observed by peers and once while not being observed. This methodology isolated changes in error monitoring (error-related negativity) and behavior (post-error reaction time slowing) as a function of social context. At 12 years, current social anxiety symptoms and lifetime diagnoses of social anxiety were obtained.ResultsChildhood BI prospectively predicted social-specific error-related negativity increases and social anxiety symptoms in adolescence; these symptoms directly related to clinical diagnoses. Serial mediation analysis showed that social error-related negativity changes explained relations between BI and social anxiety symptoms (n = 107) and diagnosis (n = 92), but only insofar as social context also led to increased post-error reaction time slowing (a measure of error preoccupation); this model was not significantly related to generalized anxiety.ConclusionResults extend prior work on socially induced changes in error monitoring and error preoccupation. These measures could index a neurobehavioral mechanism linking BI to adolescent social anxiety symptoms and diagnosis. This mechanism could relate more strongly to social than to generalized anxiety in the peri-adolescent period.

Many psychological theories posit foundational links between two fundamental constructs: (1) our ability to produce, perceive, and represent action; and (2) our ability to understand the meaning and motivation behind the action (i.e. Theory of Mind; ToM). This position is contentious, however, and long-standing competing theories of social-cognitive development debate roles for basic action-processing in ToM. Developmental research is key to investigating these hypotheses, but whether individual differences in neural and behavioral measures of motor action relate to social-cognitive development is unknown. We examined 3- to 5-year-old children's (N = 26) EEG mu-desynchronization during production of object-directed action, and explored associations between mu-desynchronization and children's behavioral motor skills, behavioral action-representation abilities, and behavioral ToM. For children with high (but not low) mu-desynchronization, motor skill related to action-representation abilities, and action-representation mediated relations between motor skill and ToM. Results demonstrate novel foundational links between action-processing and ToM, suggesting that basic motor action may be a key mechanism for social-cognitive development, thus shedding light on the origins and emergence of higher social cognition.