2.3.1 Genetic Basis of Temperament

The genetic basis of temperament traits has been theorized and supported empirically across developmental periods. Behavioral genetics studies suggest that 20–60 percent of variability in temperamental reactive (e.g., activity level, sociability, positive and negative affect) and regulatory (e.g., inhibitory control, attentional focusing) traits can be explained by genetic factors (e.g., Reference Saudino, Wang, Zentner and ShinerSaudino & Wang, 2012). In infancy, frustration, fear, and activity have been explained largely by additive genetic effects (combined effects of alleles on a single gene or two or more genes on a phenotype; Reference Goldsmith, Lemery, Buss and CamposGoldsmith et al., 1999). Reference Lemery‐Chalfant, Doelger and GoldsmithLemery-Chalfant et al. (2008) reported heritability ranging from 68–79 percent for parental reports of effortful control, and a heritability estimate of 83 percent for observer ratings of attentional control in middle childhood. In adolescence and adulthood, strong genetic contributions to harm avoidance, sensation-seeking, and reward dependence have been reported (e.g., Reference Heiman, Stallings, Hofer and HewittHeiman et al., 2003; Reference Heiman, Stallings, Young and HewittHeiman et al., 2004).

Studies have also considered associations between behavioral traits and “candidate” genes, typically considering variants of single nucleotide polymorphisms (SNP). Although there was considerable excitement about linking candidate SNPs with temperament variability, the utility of this work has been called into question because of the complexity of the human genome and genome-wide association studies (GWAS) becoming more prominent. For example, the 5-HTTLPR polymorphism in the promoter region of the serotonin transporter gene SLC6A4 has been described as demonstrating consistent and strong links with a large array of temperament tendencies as well as depression (Reference Licht, Mortensen and KnudsenLicht et al., 2011; see Reference Saudino, Wang, Zentner and ShinerSaudino & Wang, 2012 for review). Yet, a meta-analysis of data from large population-based and case-control samples (Ns ranging from 62,138 to 443,264 across subsamples), as well as preregistered analyses examining candidate gene polymorphism main effects and gene-by-environment interactions, indicated that depression candidate genes were no more associated with depression phenotypes than noncandidate genes (Reference Border, Johnson, Evans, Smolen, Berley, Sullivan and KellerBorder et al., 2019). More recent research suggests complex genetic interactions with genes critical to fetal neurodevelopment playing a role in the origins of psychopathology, wherein not only do multiple genes have synergistic effects as networks, but a single gene can have multiple effects in terms of psychological symptoms or disorders. For example, pleiotropic (i.e., associated with more than one disorder) loci within genes that show heightened expression in the brain beginning in utero and playing prominent roles in neurodevelopmental processes have been implicated in disorders such as major depression (Cross-Disorder Group of the Psychiatric Genomics Consortium, 2019), and should be considered with respect to temperament.

2.3.2 Behavioral Activation and Inhibition Systems

Approach (fight), inhibition (flight), and freeze systems rooted in the sympathetic branch of the autonomic nervous system, as well as parasympathetic and prefrontal cortex (PFC) brain systems, provide much of the biological foundation for temperament, contributing to reactivity and emotion regulation. These systems coordinate different areas of the brain as well as peripheral activity (e.g., of the vagus nerve) as a foundation for motivation, emotion, and behavior. Although some aspects of these systems and the mechanisms behind their coordination remain elusive, a great deal has been learned by relying on neuroimaging techniques.

Work examining the inhibition (flight) system is both theoretical and empirical in nature. Withdrawal motivational responses were theorized to be part of an avoidance system, which has acquired a number of different names, including behavioral inhibition system, fight–flight system (sometimes referred to as fight–flight–freeze system), and threat avoidance system. Regardless of the specific terms used, they share a common focus on responses to signals of punishment and nonreward, that is, the potential for a negative consequence. This responsiveness to punishment and nonreward includes readiness for action (arousal level) and heightened attention to cues of threat or danger. Behavioral inhibition is a tendency of some children to withdraw or react negatively in response to novelty or uncertainty, including people, places, events, and objects (Reference Garcia Coll, Kagan and ReznickGarcia Coll et al., 1984). Behavioral inhibition is typically experienced together with fear on the emotional level. Thus, the BIS is thought to support fear and avoidance, orient to cues of punishment and nonreward, and to be capable of arresting behavior that serves to achieve approach or reward-related goals (Reference Gray, McNaughton and HopeGray & McNaughton, 1996). Jerome Kagan’s work focused on behavioral inhibition, generally defined as hesitancy to approach new or unfamiliar objects or situations (Reference Kagan, Damon and EisenbergKagan, 1998). Inhibited children can be described as shy, cautious, fearful, and motorically tense, whereas uninhibited children tend to be social and outgoing (extraverted) in novel situations, and do not show as much motor restraint as inhibited children. Kagan and colleagues viewed these temperament types as reflecting individual differences in underlying biological processes, reporting a number of physiological differences between inhibited and uninhibited youngsters (e.g., Reference Kagan, Fox, Eisenberg, Damon and LernerKagan & Fox, 2006). Specifically, Kagan proposed that inhibited and uninhibited temperament types were a function of differences in the reactivity of the limbic system, and the amygdala in particular (Reference Kagan and SnidmanKagan & Snidman, 2004).

Biological models of sensitivity to reward and approach invoke the BAS in their explanations and definitions. This system is responsible for positive emotional experiences including joy, delight, or pleasure in the anticipation of reward and positive outcomes, as well as anger or frustration when reward approach and attainment are blocked, potentially resulting in aggression (Reference Gray, McNaughton and HopeGray & McNaughton, 1996). This appetitive–motivational system motivates approach behavior, including goal-directed actions and risk-taking. The neurobiological foundations for reward approach and threat-sensitive systems are described in the next subsection.

2.3.3 Left/Right Frontal Asymmetry

Well-established models describing neurobiological foundations of the BAS and the fight side of the fight–flight system, as well as the BIS and flight (and/or freeze) aspect, have focused on asymmetrical activation of the frontal cortex and lateralization of approach/avoidance activity (Reference FoxFox, 1994) using electroencephalogram (EEG) technologies to measure electrical activity. The left and right frontal cortical regions are asymmetrically related to approach and avoidance motivational and emotional tendencies. Greater trait approach and reward sensitivity are reflected in relatively stronger left-frontal activation, whereas a greater tendency toward inhibition and withdrawal is reflected in dominant right-frontal activation (e.g., Reference Calkins, Fox and MarshallCalkins et al., 1996; Reference GartsteinGartstein, 2019; Reference Hane, Fox, Henderson and MarshallHane et al., 2008). Behavioral inhibition system activation involves the amygdala, basal ganglia, and hypothalamus, all parts of the limbic system, as well as the right dorsolateral PFC and the right temporal region, associated with right-hemisphere dominance discerned via an asymmetric pattern of frontal EEG activity (Reference Kagan and SnidmanKagan & Snidman, 2004; Reference Sutton and DavidsonSutton & Davidson, 1997). The BAS recruits the corticolimbic–striatal–thalamic network and relies on dopamine pathways from the ventral tegmental area to the subcortical and frontal cortical regions, favoring left-frontal activation. Dopamine pathways involve a variety of critical functions, such as movement and neuroendocrine control, as well as reward motivation and executive functions (Reference Coan and AllenCoan & Allen, 2004; Reference Depue and CollinsDepue & Collins, 1999). Although EEG asymmetry measures electrical activity at the cortex, the pattern of lateralization – right- versus left-frontal dominance – is reflective of underlying brain activity that involves limbic structures critical to emotional processes (e.g., amygdala). The BIS and BAS are thought to work in tandem (Reference FoxFox, 1994), and this mutual regulation was recently examined across development, indicating coordinated action across the two hemispheres and links between developmental shifts in brain activity and temperament (Reference Gartstein, Hancock, Potapova, Calkins and BellGartstein et al., 2020).

2.3.4 Respiratory Sinus Arrhythmia

Respiratory sinus arrhythmia (RSA) is a widely used cardiac indicator of parasympathetic activation that has been linked to reactivity and emotion regulation in childhood (Reference BeauchaineBeauchaine, 2015). Variability in heart rate in response to respiration is mediated primarily by activity of the vagus nerve. Vagal influence diminishes during inhalation, resulting in heart rate acceleration, and increases during exhalation, causing heart rate deceleration. The characteristic respiratory rhythm of RSA provides a noninvasive measure of cardiac vagal tone and peripheral regulation (Reference PorgesPorges, 1997). Both trait-like or baseline RSA and changes in RSA in response to challenges are related to temperament. In infants, higher baseline RSA occurs with lower negativity and the need for less calming from parents (Reference Huffman, Bryan, del Carmen, Pederson, Doussard-Roosevelt and PorgesHuffman et al., 1998). In older children, high RSA is related to better social skills, more efficient mental processes, and better behavioral regulation (Reference Doussard-Roosevelt, Porges, Scanlon, Alemi and ScanlonDoussard-Roosevelt et al., 1997). Changes in cardiac vagal tone in response to challenges reflect the vagal brake through which rapid inhibition and disinhibition of vagal tone to the heart (i.e., via the sinoatrial node, which is the heart’s pacemaker) can rapidly mobilize or calm an individual. Infant research has shown the importance of the vagal brake in the regulation of social and attentional behaviors that require an awareness of the environment and the ability to engage or disengage (Reference Graziano and DerefinkoGraziano & Derefinko, 2013). Overall, trait-like RSA reflects reactive tendencies, whereas decreases in RSA during challenging encounters are markers of attention-based regulation of emotion and behavior (Reference PorgesPorges, 1997, Reference Porges2011).

2.3.5 Executive Control

Effortful control is conceptualized as the executive-based core of self-regulation, and there is considerable overlap in the conceptualization and operationalization of effortful control and executive function. Effortful control plays a role in top-down regulation of cognition, emotion, and behavior, with executive attention serving as a core mechanism (Reference Tiego, Bellgrove, Whittle, Pantelis and TestaTiego et al., 2020). Executive functioning includes attention regulation, inhibitory control, and cognitive flexibility, components that overlap with effortful control, but executive functioning also includes higher-order functions such as planning, decision-making, and problem-solving, that is, complex cognitive strategies that can arise from the application of basic executive-control processes (Reference NiggNigg, 2017). Thus, conceptually, effortful control represents the attention regulation and inhibitory core of executive functions that emerge in early childhood and serve as the basis for more complex cognitive and behavioral self-regulation capacities that develop later. Studies that simultaneously examine effortful control and executive function identify substantial overlap, including evidence of an underlying common factor (Reference Kälin and RoebersKälin & Roebers, 2021; Reference Lin, Liew and PerezLin et al., 2019; Reference Schmidt, Daseking, Gawrilow, Karbach and Kerner auch KoernerSchmidt et al., 2022; Reference Tiego, Bellgrove, Whittle, Pantelis and TestaTiego et al., 2020) composed of attentional and inhibitory control (Reference Kim-Spoon, Deater-Deckard, Calkins, King-Casas and BellKim-Spoon et al., 2019) and shared genetic influence explained by executive attention (Reference Rea-Sandin, Clifford, Doane, Davis, Grimm, Russell and Lemery-ChalfantRea-Sandin et al., 2023).

Attention processes present in infancy contribute to executive-control development (Reference Marcovitch, Clearfield, Swingler, Calkins and BellMarcovitch et al., 2016). This executive attention-based regulatory capacity emerges in early childhood, with marked increases occurring from two to six years of age (e.g., Reference Carlson, Davis and LeachCarlson et al., 2005) and continued growth at a moderate rate throughout childhood (Reference LenguaLengua, 2006; Reference Lensing and ElsnerLensing & Elsner, 2018; Reference PoonPoon, 2018). A critical milestone involves a shift away from reliance on the alerting attention network, which is primarily externally driven (e.g., responding to salient visual and auditory cues, like a sudden loud noise; Reference Posner, Rothbart, Sheese and VoelkerPosner et al., 2012; Reference Rothbart, Ellis, Rosario Rueda and PosnerRothbart et al., 2003), to a more flexible executive-attention network, including the anterior cingulate cortex (ACC), basal ganglia, and areas of the PFC under dopamine modulation, with which attention becomes more internally driven and goal-directed. This shift in the dominance of attention systems is accompanied by physical maturation of brain structures, network connectivity changes, and a shift in predominant neurotransmitters involved, supporting advanced self-regulation (Reference Rothbart, Ellis, Rosario Rueda and PosnerRothbart et al., 2003). The executive network provides the foundation for control of working memory, monitoring conflict and conflict resolution, response to error, and selecting preferred responses between alternative options (e.g., Reference Posner, Rothbart, Sheese and VoelkerPosner et al., 2012; Reference Rothbart, Ellis, Rosario Rueda and PosnerRothbart et al., 2003).

Studies link effortful control with brain activation in several domains. In a meta-analysis, EEG alpha power, a measure of engagement in self-regulatory processes, was related to executive functions in infants and young children (Reference Hofstee, Huijding, Cuevas and DekovićHofstee et al., 2022). Parent-reported effortful control in four- to five-year-old children was related to better performance on a cognitive flexibility task and less activation of the dorsolateral PFC (Reference Quiñones-Camacho, Fishburn, Camacho, Wakschlag and PerlmanQuiñones-Camacho et al., 2019). In children aged six and older, as well as in young adults, N2 and P3 event-related potential (ERP) components reflect activity in the ACC and PFC and represent executive attention and inhibitory control. Recognition of conflict or the inhibition of a prepotent response is reflected in N2 (Reference Buss, Dennis, Brooker and SippelBuss et al., 2011; Reference Zordan, Sarlo and StablumZordan et al., 2008), and P3 is related to attentional monitoring and evaluation of stimuli (e.g., Reference Rueda, Posner, Rothbart, Baumeister and VohsRueda et al., 2004). In middle childhood, the development of effortful control is linked with the maturation of resting state networks, in particular the default-mode (DMN) and task-positive networks (TPN). The DMN has been proposed to play a critical role in preplanned behaviors, executive behavior, and reward processing, and the TPN is important for behavioral control. Development of these systems appears to be a prerequisite for the development of attentional and behavioral control (Reference Knyazev, Savostyanov, Bocharov, Slobodskaya, Bairova, Tamozhnikov and StepanovaKnyazev et al., 2017).

The implications of activity in these neural systems for children’s social, emotional, and behavioral adjustment might be accounted for by the interplay between executive and emotion processes. Both hyper- and hypo-arousal of reactivity systems are associated with lower attentional and affective control (Reference WassWass, 2021). Greater relative right-frontal cortical activity is associated with withdrawal motivation and negative affect, but it is also associated with greater regulatory control (Reference Gable, Neal and ThreadgillGable et al., 2018), and greater relative right activation may be associated with effortful control of emotions rather than negative affectivity itself (Reference Lacey, Neal and GableLacey et al., 2020). Neural activity related to greater executive control is expected to underlie regulation of emotional reactions, particularly negative emotions, by facilitating attentional shifting away from threatening stimuli, inhibitory control of cognitive biases, and minimizing prepotent or impulsive cognitive and behavioral responses, particularly in response to stressful experiences and contexts.

2.3.6 HPA Axis

Activity of the stress-sensitive HPA system has been linked with temperament, with the primary focus on modulating the effects of exposure to stress (e.g., Reference Gunnar, Sebanc, Tout, Donzella and van DulmenGunnar et al., 2003). Activation of the HPA axis results in the release of cortisol, and minimally invasive procedures allow for its measurement, making cortisol the most frequently studied component of the psychobiology of stress responsiveness. The HPA axis displays a diurnal rhythm with the highest levels of cortisol typically occurring in the morning and decreasing across the day, with the lowest levels near bedtime (Reference Kirschbaum, Ehlert, Piedmont and HellhammerKirschbaum et al., 1990). Laboratory-induced stressors have been used widely to examine HPA reactivity through measuring cortisol prior to and again following an experimental manipulation in research with infants, children, and adults. Research has also leveraged changes in the diurnal cortisol rhythm in response to stressors encountered in everyday life to understand HPA functioning and the role of temperament in stress responses – for example, at the beginning of the school day (Reference Turner-Cobb, Rixon and JessopTurner-Cobb et al., 2008).

In preschool-age children, higher surgency and lower effortful control were associated with elevated cortisol, with aggressive behaviors and peer rejection mediating this association (Reference Gunnar, Sebanc, Tout, Donzella and van DulmenGunnar et al., 2003). Specifically, more surgent children with lower effortful control tended to exhibit more aggression; this translated into peer rejection, which was in turn linked with higher cortisol levels. Low positive emotionality was also associated with higher morning cortisol for preschool-age children whose mothers reported a history of depression (Reference Dougherty, Klein, Olino, Dyson and RoseDougherty et al., 2009). Reference Spinrad, Eisenberg, Granger, Eggum, Sallquist, Haugen and HoferSpinrad et al. (2009) measured salivary cortisol levels in preschoolers before and after a frustrating task. Engaging in the task resulted in an elevation of cortisol for a portion of the preschool sample (52 percent) and higher cortisol reactivity scores – the difference between cortisol levels at pretest and at the end of the laboratory visit (approximately forty minutes posttest). These patterns were associated with greater mother-reported effortful control.

Stressful experiences, such as child maltreatment, influence the development of stress-responsive neurobiological systems, especially if the stressful experiences occur during periods of rapid brain development (Reference Loman and GunnarLoman & Gunnar, 2010; Reference Shannon, Champoux and SuomiShannon et al., 1998). Lower socioeconomic status (SES) is associated with both elevated and blunted diurnal cortisol patterns in children and adolescents (Reference Dowd, Simanek and AielloDowd et al., 2009), suggesting that either form of altered HPA-axis functioning may indicate a disrupted or inflexible stress-response system (Reference Blair, Granger, Willoughby, Mills-Koonce, Cox, Greenberg, Kivlighan and FortunatoBlair et al., 2011; Reference Bruce, Fisher, Pears and LevineBruce et al., 2009).

Importantly, consistently high levels of cortisol are thought to have detrimental effects on the functioning of the HPA system by damaging the regulatory mechanism which appears to lose the sensitivity required for effective control, no longer increasing and decreasing concentrations dependent on environmental circumstances. In fact, long-term exposure to adversity seems to result in hypocortisolism, or consistently low levels of cortisol, attributed to this HPA dysregulation (Reference Heim, Ehlert and HellhammerHeim et al., 2000; Reference Koss, Mliner, Donzella and GunnarKoss et al., 2016). The relation of HPA reactivity or cortisol concentrations with top-down control afforded by executive functions may be bidirectional, as high cortisol concentrations appear to disrupt the development of executive control, whereas deficient executive functions have been linked with excessive HPA reactivity (Reference Blair, Granger, Willoughby, Mills-Koonce, Cox, Greenberg, Kivlighan and FortunatoBlair et al., 2011; Reference Lengua, Thompson, Moran, Zalewski, Ruberry, Klein and KiffLengua et al., 2020; Reference Wagner, Cepeda, Krieger, Maggi, D’Angiulli, Weinberg and GrunauWagner et al., 2016). This disruption of executive function development may be one important mechanism behind the contribution of environmental adversity to poor self-regulation. Parenting has been shown to mediate the impact of adversity, especially poverty-related chronic stress, on HPA-axis functioning. For example, maternal negativity accounts for the effect of cumulative family risk on lower morning cortisol levels for preschool-age children (Reference Zalewski, Lengua, Kiff and FisherZalewski et al., 2012). The latter is important because evidence of the effects of modifiable mediators, such as parenting, provides an avenue for potential prevention or early intervention, wherein, for example, parents could be supported to respond to their children with warm, sensitive, and consistent parenting behaviors.

5.1.1 Fear Reactivity and Emerging Effortful Control

Many important developmental milestones are achieved in the first two years of life. With regard to aspects of temperament reactivity and regulation, fear development at the end of the first year and the emergence of attention-based regulation in the second year are likely two of the most critical. Both developmental processes are context dependent, with family and parenting factors playing a role in shaping their unfolding.

There are normative increases in fear in infancy, particularly during the latter half of the first year of life, as inhibition of approach toward novel or intense stimuli emerges (Reference Carranza, Pérez-López, Salinas and Martínez-FuentesCarranza et al., 2000; Reference RothbartRothbart, 1986, Reference Rothbart1988). Growth modeling studies indicate nonlinear increases in fearfulness across infancy (Reference Braungart-Rieker, Hill-Soderlund and KarrassBraungart-Rieker et al., 2010; Reference Gartstein, Hancock and IversonGartstein et al., 2018). These intensive longitudinal evaluations of behavioral fear provide evidence of a rapid increase between eight and ten months of age, which is consistent with earlier studies (Reference RothbartRothbart, 1988). Individual variation in growth in fear related to temperament differences have implications for later outcomes. For example, steeper increases in fearfulness are associated with greater toddler anxiety (Reference Gartstein, Bridgett, Rothbart, Robertson, Iddins, Ramsay and SchlectGartstein et al., 2010). In addition, inhibited temperament in the second year of life predicts increased social anxiety in adolescence (Reference Schwartz, Snidman and KaganSchwartz et al., 1999), and “high reactive” infants demonstrated a greater functional magnetic resonance imaging (fMRI) signal response in the amygdala to a presentation of novel faces (associated with anxiety) two decades later (Reference Schwartz, Wright, Shin, Kagan and RauchSchwartz et al., 2003).

The regulatory domain of temperament is typically conceptualized as effortful control (Reference Bridgett, Burt, Edwards and Deater-DeckardBridgett et al., 2015; Reference Gartstein, Putnam, Aaron, Rothbart and MatzmanGartstein et al., 2016). Origins of effortful control coincide with maturation of the frontal lobes and advances in executive functions. According to Reference RothbartRothbart (2011), effortful control is based on the development of the executive-attention system and provides children with self-regulation and flexibility to approach objects or situations that elicit fear, or to avoid others that appear rewarding, as needed. Characteristics reflective of effortful control (e.g., flexible, voluntary control of attention, inhibitory control) are associated with development of the executive-attention system (Reference Spinrad, Eisenberg and GaertnerSpinrad et al., 2007). Whereas the orienting attention network dominant during early infancy is modulated by the cholinergic system, the executive-attention network begins to exert its influence at the end of the first year of life and is primarily moderated by dopaminergic input from the ventral tegmental area (Reference Posner, Rothbart, Sheese and VoelkerPosner et al., 2012). A number of conceptual distinctions have been made in regard to emotion regulation, and effortful control is understood to broadly support such efforts, be they focused on modulating emotion itself or on its outward expression starting at the end of the first year of life (Reference Eisenberg, Spinrad, Fabes, Reiser, Cumberland, Shepard and ThompsonEisenberg et al., 2004; Reference RothbartRothbart, 2011).

Earlier regulatory capacity dependent on orienting attention sets the stage for development of effortful control (Reference Gartstein, Bridgett, Young, Panksepp and PowerGartstein et al., 2013; Reference Putnam, Rothbart and GartsteinPutnam et al., 2008). Specifically, infants who persist in attending to stimuli, as well as soothe more easily in response to parental efforts, enjoy physical contact with caregivers and more low-intensity activities or stimuli, and show more advanced flexible and voluntarily controlled attentional skills associated with executive functions. Approach and avoidance tendencies have also been implicated in the development of effortful control and the establishment of closely linked executive functions. According to Reference Kochanska and KnaakKochanska and Knaak (2003), fearfulness may facilitate the development of effortful control. However, a negative relation between executive functions and shyness has been demonstrated (Reference Blankson, O’Brien, Leerkes, Marcovitch and CalkinsBlankson et al., 2011), suggesting a complex pattern of effects mixed in direction, with positive and negative associations between fear/shyness and executive functions contributing to effortful control. Approach-related findings also lack consistency, insofar as infant surgency is linked with higher effortful control; however, surgency at eighteen months predicts later effortful control in the negative direction (Reference Gartstein, Slobodskaya, Putnam and KinshtGartstein et al., 2009; Reference Putnam, Rothbart and GartsteinPutnam et al., 2008). This pattern of results could be a function of not adequately capturing dynamic developmental processes or the components of surgency operating differently. The variability may also be a function of moderation effects conferred by parenting, which alter the nature of approach and avoidance links with effortful control.

5.1.2 Parent–Infant Interactions and Relationship

Parent–infant interactions represent a critical aspect of the infant’s social milieu that contributes to the development of effortful control and self-regulation. The brain undergoes dramatic changes during the first years of life, including an overproduction of synapses followed by pruning. The synapses that remain are thought to be experience-dependent (Reference KolbKolb, 2018), and parents play a central role in structuring infants’ experiences, including social interactions. Reference Bernier, Calkins and BellBernier et al. (2016) found that maternal positive affect was associated with EEG markers relevant to cognitive and emotional functioning, namely, higher baseline frontal theta (4–6 Hz) and alpha (6–9 Hz) at ten and twenty-four months of age. Importantly, maternal positive affect was observed at five months of age, at which time links between brain development and maternal behavior had not emerged. This “sleeper” effect likely reflects the accumulation of parent–infant interaction influences on the child’s brain over time and underscores the need to investigate relations between parent–infant exchanges and children’s brain development longitudinally. As noted, parent–child interactional factors, critical because of their ubiquitous nature, can be expected to moderate links between approach/avoidance and emerging regulation in infancy and across early childhood, modulating their contributions to the development of top-down control enabled by executive function. The dynamics driven by these factors are experienced on a daily basis over “multiple trials” shaping developmental changes that serve to establish self-regulation and related processes.

Parent–child interactions represent critical contributors to the development of approach and avoidance systems and their affective components (Reference Buss, Kiel, Vasa and RoyBuss & Kiel, 2013; Reference Fox, Henderson, Rubin, Calkins and SchmidtFox et al., 2001), with most studies examining parental sensitivity or responsiveness. For example, infants with more sensitive mothers show slower increases in fear between four and sixteen months of age (Reference Braungart-Rieker, Hill-Soderlund and KarrassBraungart-Rieker et al., 2010). High infant reactivity to novelty predicts toddler anxiety when mothers are less sensitive at six months of age (Reference Crockenberg and LeerkesCrockenberg & Leerkes, 2006). Maternal sensitivity also appears to serve a protective function relative to fear and right-frontal activation early in infancy (e.g., Reference Hardin, Jones, Mize and PlattHardin et al., 2021). Reference Glöggler and Pauli-PottGlöggler and Pauli-Pott (2008) found that children of more sensitive mothers engaged in greater active regulation in a fear-eliciting situation, which could explain this protective effect. With respect to other elements of mother–infant interactions, reciprocity has been linked with slower increases in fearfulness across the first year of life, and the tempo of interactions with lower levels of fear at four months (Reference Gartstein, Hancock and IversonGartstein et al., 2018). In examining approach systems, reciprocity and positive emotional tone of mother–infant interactions predict positive affectivity in four-month-old infants, whereas tempo of interactions is associated with steeper growth of positive affectivity across infancy (Reference Gartstein, Hancock and IversonGartstein et al., 2018).

Protective effects of sensitive, responsive parent–child interactions have been noted with respect to fear and avoidance. However, these effects do not appear to be uniform. Sensitivity to distress and nondistress both appear to be protective earlier in infancy (Reference Leerkes, Blankson and O’BrienLeerkes et al., 2009, Reference Leerkes, Weaver and O’Brien2012). However, maternal sensitivity to distress tends to promote later fearful behavior, as older infants exhibiting behavioral inhibition are more likely to remain inhibited when mothers are consistently sensitive to their negative affect (Reference Arcus, Wachs, McCrae and KohnstammArcus, 2001; Reference Buss, Kiel, Vasa and RoyBuss & Kiel, 2013). Similarly, Reference Park, Belsky, Putnam and CrnicPark et al. (1997) reported that sensitive, nonintrusive parenting contributed to increased fearfulness for infants high in negative emotionality, and oversolicitious maternal behavior to increased inhibition for already-fearful children (Reference Rubin, Hemphill, Chen, Hastings, Sanson, Coco and & CuiRubin et al., 2006). Highly responsive mothers, who are not intrusive or overprotective, may nonetheless inadvertently decrease opportunities for internal modulation of affect by externally regulating infant distress; this is more critical later in infancy as flexible attention-based self-regulation begins to emerge (Reference Posner, Rothbart, Sheese and VoelkerPosner et al., 2012). The most convincing evidence that excessive sensitivity facilitates rather than dampens behavioral inhibition, increasing the risk of anxiety, comes from work with toddlers that examined maternal reactions to fear displays (Reference Buss and KielBuss & Kiel, 2011; Reference Kiel and BussKiel & Buss, 2012). Moderate levels of maternal sensitivity may be optimal, as both very high and low levels are likely to increase anxiety-related risk for children already demonstrating considerable fearfulness (e.g., Reference Buss, Kiel, Vasa and RoyBuss & Kiel, 2013).

Although maternal contributions to temperament development have been studied most extensively in infancy, other family members, of course, play a role as well. Fathers and extended family, as well as broader community structures including day-care facilities, provide important support for early social–emotional development. Mothers and fathers have been described as providing similar temperament ratings across the first year of life (Reference Sechi, Vismara, Rollè, Prino and LucarelliSechi et al., 2020), and there is also evidence that symptoms of anxiety and depression for mothers and fathers have similar associations with greater infant negative emotionality (e.g., Reference Sechi, Vismara, Rollè, Prino and LucarelliSechi et al., 2020). However, some mother–father differences are notable. For example, Reference Ventura and StevensonVentura and Stevenson (1986) reported that the temperament ratings of one parent accounted for less than 50 percent of variance in the other parent’s scores. In that study, mothers described their infants as more soothable and less fearful than fathers described them. Reference Sechi, Vismara, Rollè, Prino and LucarelliSechi et al. (2020) also identified differences in maternal and paternal ratings of infant temperament, with mothers reporting more motor activity compared to fathers at three months of age, whereas at twelve months mothers perceived their infants as higher in positive affectivity compared to fathers. Fathers may be more influenced by their child’s gender than mothers when providing temperament ratings (Reference Bayly and GartsteinBayly & Gartstein, 2013; Reference Parade and LeerkesParade & Leerkes, 2008) and may also respond differentially to child temperament attributes in terms of their parenting (Reference Padilla and RyanPadilla & Ryan, 2019). Whereas mothers appeared less sensitive, more intrusive, and more detached with children who scored low in sociability, fathers unexpectedly engaged in more educational activities with children higher in negative emotionality.

The quality of paternal interactions with young children depends on broader paternal involvement as well as child temperament (Reference Cerniglia, Cimino and BallarottoCerniglia et al., 2014). Specifically, a better quality of father–infant interactions was associated with greater involvement overall, but only in the context of higher child social orientation. Reference Mehall, Spinrad, Eisenberg and GaertnerMehall et al. (2009) reported that marital satisfaction mediated the association between infant regulation and parental involvement, contemporaneously for mothers and longitudinally for fathers. It was noted that fathers begin to engage with their children later in infancy, and contextual factors such as marital quality become more important over time, impacting the level of their involvement.

Another important domain of the parent–child relationship has to do with the development of secure attachment – linked with more sensitive and responsive parent–child interactions (Reference AinsworthAinsworth, 1979) and shown to predict a number of important child outcomes, such as social competence (Reference Goldsmith and HarmanGoldsmith & Harman, 1994). There is a modest association between negative temperament (negative emotional reactivity) and infants’ attachment security with mothers, with an insecure attachment characterized by resistance being more strongly related to temperament than secure or avoidant attachment (Reference Groh, Narayan, Bakermans‐Kranenburg, Roisman, Vaughn, Fearon and van IJzendoornGroh et al., 2017). No significant association was found between negative temperament and father–child attachment (Reference Groh, Narayan, Bakermans‐Kranenburg, Roisman, Vaughn, Fearon and van IJzendoornGroh et al., 2017). Multiple intervention approaches for enhancing sensitivity and responsiveness in parent–child interactions are available. Some of these approaches target infants high in negative emotionality in particular, as these children have been shown to be at an increased risk of insecure attachment (Reference Calkins and FoxCalkins & Fox, 1992). An early example of such an approach was implemented by Reference van den Boomvan den Boom (1995), who delivered a brief intervention to mothers with infants high in irritability to enhance mothers’ sensitivity and responsiveness to their cues. This intervention not only increased the security of attachment for participating infants, it resulted in lasting benefits, with improved child cooperation and peer interactions in later years (Reference van den Boomvan den Boom, 1995). In another study, an intervention aimed at enhancing infant secure attachment had moderated effects such that the intervention had the intended effect for highly irritable infants only, indicating a particular benefit of sensitive, responsive parenting to irritable infants’ attachment security (Reference Cassidy, Woodhouse, Sherman, Stupica and LejuezCassidy et al., 2011).

5.1.3 Family Relationships

Infant temperament has also been examined in a broader family context, although this work has been somewhat limited to date. In one study, three-and-a-half-month-old infants’ temperamental characteristics (fussiness and unadaptability) were assessed along with marital satisfaction and co-parenting behaviors (Reference Schoppe-Sullivan, Mangelsdorf, Brown and SokolowskiSchoppe-Sullivan et al., 2007). Associations between infant temperament and co-parenting behaviors varied as a function of marital quality, so that for families with high marital quality more optimal co-parenting was observed in the context of a challenging temperament profile, whereas at low levels of marital quality co-parenting behavior when caring for a challenging infant was less effective.

Reference Wong, Mangelsdorf, Brown, Neff and Schoppe-SullivanWong et al. (2009) examined parental beliefs about the importance of the paternal caregiving role, infant temperament, and marital quality as predictors of attachment security with both parents, after accounting for their sensitivity. For mothers, describing the paternal caregiving role as important was associated with less secure attachment, but only at high levels of infant fussiness. For fathers, the pattern of results was different: Their view of the paternal caregiving role as important was associated with a greater likelihood of having securely attached infants when levels of infant fussiness or marital quality were also rated as high. Child effects in this context are also notable; for example, mothers and fathers of infants with greater regulatory capacity express higher levels of marital satisfaction (Reference Mehall, Spinrad, Eisenberg and GaertnerMehall et al., 2009). There is also evidence that fathers are more engaged in parenting when their daughters are higher in sociability (Reference McBride and MillsMcBride & Mills, 1993) and their sons are described as “easy” in terms of their temperament (Reference Manlove and Vernon-FeagansManlove & Vernon-Feagans, 2002). A more nuanced understanding of the role of temperament in early childhood development is obtained when multiple family relationships are considered simultaneously.

5.1.4 Childcare

Temperament-related effects have also been studied in the context of early childcare experiences. Reference Watamura, Donzella, Alwin and GunnarWatamura et al. (2003) showed that, while children cared for in their homes typically demonstrated decreases in cortisol levels from morning to afternoon, in a day-care setting cortisol levels increased for many infants and toddlers. Importantly, those described as higher in social fear compared to less fearful children exhibited elevated afternoon cortisol and larger cortisol increases across the day in a childcare setting. Other studies have taken advantage of the childcare context to examine whether children with different temperament profiles would be differentially susceptible to the quality of caregiving effects. Reference Pluess and BelskyPluess and Belsky (2009) reported that, compared to toddlers lower in negative emotionality, toddlers higher in negative emotionality exhibit more behavior problems and less social competence in low-quality childcare but fewer behavior problems and greater social competence in high-quality childcare settings. This pattern of results is consistent with the “for better and for worse” differential susceptibility hypothesis, wherein children with more challenging profiles perform poorly under conditions of adversity, yet demonstrate superior outcomes when exposed to enriched environments. However, such support has not been uniformly found across relevant studies. For example, contrary to expectations, children low in self-regulation (i.e., demonstrating dysregulated behavior) were no more vulnerable to relatively low-quality day care or more susceptible to day-care effects more generally, compared to their better-regulated counterparts (Reference Broekhuizen, van Aken, Dubas, Mulder and LesemanBroekhuizen et al., 2015). Higher levels of shyness, frustration, and soothability predict greater social competence and better social–emotional adjustment for infants and toddlers attending Dutch day care. Although supportive interactions between caregivers and children predicted child well-being and competence, no interaction effects indicative of differential susceptibility to day-care quality were observed (Reference FukkinkFukkink, 2022).

5.1.5 Physical Health

Temperament also contributes to important aspects of physical health, among them sleeping, feeding/eating, and risk of childhood obesity. Prior studies linking temperament to sleeping and eating/feeding in childhood have unearthed associations between temperament-related challenges and eating and sleeping problems. For example, fussy–difficult temperament is associated with sleeping problems (more frequent night wakings and difficulties settling down to sleep) at one year of age and persistent sleeping problems at two years of age (Reference Morrell and SteeleMorrell & Steele, 2003). Reference KelmansonKelmanson (2004) reported that more distress-prone infants were more likely to have problems sleeping throughout the night and needed parental interaction more frequently before falling back asleep.

Infants described as more challenging in terms of their temperament are also more likely to have difficulties with feeding. For infants in Barbados, difficult temperament was associated with feeding difficulties and greater parental involvement during feeding (Reference Galler, Harrison, Ramsey, Butler and FordeGaller et al., 2004). Infants with feeding disorders were more frequently rated as having a difficult temperament, with their caregivers describing these infants as fussy and difficult to soothe (Reference Feldman, Keren, Gross-Rozval and TyanoFeldman et al., 2004). More difficult temperament and higher levels of negative emotionality (frustration in particular) are associated with higher weight in cross-sectional studies and more significant weight gain in longitudinal investigations (Reference CareyCarey, 1985; Reference Darlington and WrightDarlington & Wright, 2006; Reference Hittner, Tripicchio and FaithHittner et al., 2016; Reference Niegel, Ystrom and VollrathNiegel et al., 2007). Surgency is also related to greater weight gain and higher BMI (Reference Burton, Wells, Kennedy, Nicholl, Khakoo and FewtrellBurton et al., 2011).

These findings have been interpreted to mean that infants and toddlers who present caregivers with temperament challenges may be at risk of sleeping and eating problems, as well as childhood obesity. With respect to sleep, these children may be particularly resistant to bedtime routines, struggling with returning to sleep when awakened at night. For feeding, displays of distress at mealtimes may lead to less effective parental efforts, or may involve more frequent feeding and reliance on calorically dense foods in order to soothe/lower the level of arousal, which can translate into risk of obesity. However, this literature is not entirely consistent; for example, Reference Worobey, Peña, Ramos and EspinosaWorobey and colleagues (2014) demonstrated that feeding frequency in infancy is not a function of difficult temperament displays.

Temperament and infant physical health may have reciprocal effects, as evidence suggests that health indicators have implications for temperament development. For example, one study showed that better sleeping behaviors in a sample of primarily Black and White infants and toddlers living in low-income homes were related to better effortful control (Reference Bates, Singletary, Dynia and JusticeBates et al., 2021). Another study showed that higher BMI was prospectively associated with lower effortful control in early childhood, mediating the effects of low income on effortful control (Reference Tandon, Thompson, Moran and LenguaTandon et al., 2015).

Taken together, the evidence consistently points to the parent–child relationship, parenting, and caregiving settings as both shaping and being shaped by infant temperament. These early relationships lay the foundation for emotional reactivity and self-regulation, as well as for social, emotional, and behavioral adjustment and physical health as children transition into middle childhood.

5.2.1 Parenting

Parenting and the parent–child relationship are key influences on children’s development in middle childhood and preadolescence. There is consistent evidence of reciprocal relations between parenting and children’s temperament, with temperament both shaping and being shaped by parent behaviors, supporting a transactional process (Reference Kiff, Lengua and ZalewskiKiff et al., 2011). With regard to children’s negative emotionality, harsh, unsupportive parenting predicts higher negative emotionality (e.g., Reference Scaramella, Sohr-Preston, Mirabile, Robison and CallahanScaramella et al., 2008), whereas warm and sensitive parenting is associated with decreases in negative emotionality (e.g., Reference Bates, Pettit, Grusec and HastingsBates & Pettit, 2007; Reference Bates, Schermerhorn, Petersen, Lewis and RudolphBates et al., 2014). At the same time, negative emotionality affects parenting. High reactivity in preschool children predicts more coercive parenting (Reference Gölcük and BerumentGölcük & Berument, 2021), and preschool “hard to manage” temperament predicts more power-assertive parenting in middle childhood, particularly when families are low in resources (parents who are younger, lower education, low income; Reference Kim and KochanskaKim & Kochanska, 2020). In addition, inconsistent discipline is related to increases in negative emotionality in children, while child irritability predicts increases in inconsistent discipline by parents (Reference Lengua and KovacsLengua & Kovacs, 2005). Infants classified as low reactive had mothers who were more likely to employ reasoning as a response to verbal conflict when children reached middle childhood (Reference Hardway, Kagan, Snidman and PincusHardway et al., 2013). There may be some differentiation of the relations of fear and frustration as components of negative emotionality with parenting. Fearfulness may draw for more warm and supportive parenting (Reference LenguaLengua, 2006), and make children easier to discipline, predicting more compliance in toddlers (Reference Kochanska, Coy and MurrayKochanska et al., 2001; Reference van der Mark, Bakermans-Kranenburg and van Ijzendoornvan der Mark et al., 2002). In contrast, frustration appears to consistently elicit more negative parenting (Reference Kiff, Lengua and ZalewskiKiff et al., 2011).

Clear or consistent limit-setting (Reference Taylor, Eisenberg, Spinrad and WidamanTaylor et al., 2013), scaffolding (Reference Lengua, Kiff, Moran, Zalewski, Thompson, Cortes and RuberryLengua et al., 2014), and warmth (Reference Klein, Lengua, Thompson, Moran, Ruberry, Kiff and ZalewskiKlein et al., 2018) support the development of effortful control. In turn, effortful control predicts parenting. Lower inhibitory control predicts increased maternal hostility (Reference Leve, Griffin, Natsuaki, Harold, Neiderhiser, Ganiban and … & ReissLeve et al., 2019), and higher effortful control predicts lower maternal negativity (Reference Klein, Lengua, Thompson, Moran, Ruberry, Kiff and ZalewskiKlein et al., 2018) and more positive parenting (Reference Soydan and AkalinSoydan & Akalin, 2022), indicating that more regulated children elicit more positive parent behaviors, leading to better developmental outcomes.

Additionally, child temperament and parenting interact to predict child outcomes, with the influence of parenting increased or decreased in magnitude, or even altered in direction, by child temperament characteristics. Child frustration tends to be related to higher levels of problem outcomes over and above parenting effects and exacerbates the effects of negative parenting, whereas effortful control generally mitigates the effects of negative parenting (e.g., Reference Kiff, Lengua and ZalewskiKiff et al., 2011). For example, children with low effortful control show greater externalizing symptoms in response to more punishing parenting than children with higher effortful control (Reference Ezpeleta, Penelo, Osa, Navarro and TrepatEzpeleta et al., 2019). The goodness-of-fit model provides a nuanced understanding of how temperament interacts with the environment and experiences, articulating that children benefit from environments that match their temperament (Reference Chess, Thomas, Strelau and AngleitnerChess & Thomas, 1991). For example, gentle discipline predicts compliance and internalization of rules for fearful but not for low-fear children (Reference KochanskaKochanska 1995, Reference Kochanska1997), whereas fearful temperament exacerbates the negative effects of power-assertive or harsh parenting; low-fear children, however, do not seem to be adversely affected by these parenting behaviors (e.g., Reference Kochanska, Aksan and JoyKochanska et al., 2007). Also, more inhibited children at age three who receive more structured parenting at age five show lower internalizing symptoms (Reference Liu, Kryski, Smith, Joanisse and HaydenLiu et al., 2019), whereas more overprotective behaviors toward fearful children predict an increase in internalizing problems (Reference Buss, Zhou and TrainerBuss et al., 2021). Additionally, children who are high in surgency or impulsivity may benefit more from parental guidance in the development of effortful control, and struggle more when they are less supported or receive less structure (Reference Shimomaeda, Thompson and LenguaShimomaeda et al., 2023; Reference Suor, Sturge-Apple, Davies and Jones-GordilsSuor et al., 2019). Temperament alters children’s responses to parent behaviors, with effective parenting varying based on child temperament.

5.2.2 Family Relationships

Family relationships, including family conflict and cohesion, as well as sibling relationships, represent key socialization experiences in middle childhood and preadolescence. Low family cohesion, that is a family’s emotional bonds and sense of closeness (Reference Goodrum, Smith, Hanson, Moreland, Saunders and KilpatrickGoodrum et al., 2020; Reference Haddad, Barocas and HollenbeckHaddad et al., 1991), and high family conflict disrupt family stability, straining the parent–child relationships as well as sibling–sibling relationships. Child temperament influences how a child contributes and responds to the family environment. Children with more vulnerable or difficult temperament characteristics, such as higher negative emotionality or impulsivity, might struggle to cope effectively in a context of high conflict. Preschool children with more difficult temperaments exhibit greater internalizing and externalizing problems in high-conflict families compared to children with easy temperaments, who had fewer problems regardless of level of family conflict (Reference Tschann, Kaiser, Chesney, Alkon and BoyceTschann et al., 1996). Similarly, interparental conflict is related to children’s problem behaviors for children high in irritability, but not for those low in irritability (Reference Hentges, Davies and CicchettiHentges et al., 2015). Negative emotionality also moderates the relation between family cohesion and child well-being, with children higher in negative reactivity showing lower well-being in a context of low family cohesion than children lower in negative reactivity (Reference Myerberg, Rabinowitz, Reynolds and DrabickMyerberg et al., 2019). Family context also shapes children’s temperament. For example, lower family cohesion and greater conflict predict higher levels of child fearfulness (Reference Lucia and BreslauLucia & Breslau, 2006). Finally, children contribute to these family dynamics. For example, higher effortful control is associated with increased positive involvement and communication between parents and children, regardless of parents’ level of marital satisfaction (Reference Ato, Galián and Fernández-VilarAto et al., 2015).

5.2.3 Siblings

Sibling relationships, which are affected by family cohesion and conflict (Reference Brody, Stoneman and McCoyBrody et al., 1994; Reference Zemp, Friedrich, Schirl, Dantchev, Voracek and TranZemp et al., 2021) and by marital hostility (Reference Dunn, Deater-Deckard, Pickering and GoldingDunn et al., 1999), also relate to children’s temperament (Reference Brody, Stoneman and McCoyBrody et al., 1994; Reference Stocker, Dunn and PlominStocker et al., 1989), which in turn interacts with birth order and differential parental treatment (e.g., Reference Qian, Chen, Jiang, Guo, Tian and DouQian et al., 2022; Reference Stocker, Dunn and PlominStocker et al., 1989). In older siblings, shyness is associated with more positive sibling relationships (i.e., less control and competitiveness), whereas degree of emotional upset is associated with more negative relationships (Reference Stocker, Dunn and PlominStocker et al., 1989). In younger siblings, the degree of emotional upset is associated with a negative sibling relationship, whereas sociability is associated with less cooperation but a more positive relationship overall (Reference Stocker, Dunn and PlominStocker et al., 1989). For both older and younger siblings, differential parental treatment directed at one sibling is related to poorer sibling relationships (e.g., Reference Stocker, Dunn and PlominStocker et al., 1989). Furthermore, child gender may moderate associations between temperament and sibling relationships. In a sample of same-sex siblings, emotional intensity and low persistence were both associated with increased agonistic behavior between sisters, and each sibling’s temperament contributed equally to this dynamic. For brothers, only the younger brother’s high activity and low persistence predicted more agonistic behavior (Reference Brody, Stoneman and McCoyBrody et al., 1994).

5.2.4 Neighborhood

There has been relatively little research on how neighborhood context shapes temperament in middle childhood or preadolescence. One exception is Reference Hart, Atkins and MatsubaHart et al. (2008), who used two waves of data from the child sample of the National Longitudinal Survey of Youth (National Longitudinal Surveys, n.d.), the first when children were three to four years of age, and again two years later. Neighborhood economic disadvantage was associated with children’s undesirable personality/temperament change (decreases in resiliency and overcontrol and increases in undercontrol) after controlling for family-level characteristics. These investigators further tested whether maternal depression, Head Start participation, cognitive and emotional support in the home, or maternal trust in the neighborhood mediated the relation between neighborhood economic deprivation and temperament change, but no evidence of mediation was found (Reference Hart, Atkins and MatsubaHart et al., 2008). Using data from the Longitudinal Study of Australian Children (Australian Institute of Family Studies, 2015) that followed children from four to fifteen years of age, Reference Strickhouser and SutinStickhouser and Sutin (2020) examined the joint associations of family and neighborhood socioeconomic disadvantage with three temperament traits (sociability, reactivity, and persistence). After controlling for family SES, greater neighborhood disadvantage at baseline was associated with children’s lower sociability and higher reactivity, and these relations were stable over time.

Temperament can moderate the impact of neighborhood context on other domains of child development. For example, using an urban community sample of eight-to-twelve-year-old children, Reference Bush, Lengua and ColderBush and colleagues (2010) found that neighborhood problems (measured by parent and observer ratings) were more strongly related to lower social competence for more fearful than for less fearful children and for less irritable than for more irritable children. Moreover, neighborhood social organization was more strongly associated with higher social competence for low-fear children than higher-fear children. In a sample of youth aged ten to twelve years, selected on the basis of the presence or absence of a paternal history of substance use disorder or other psychiatric disorders, Reference Rabinowitz, Drabick and ReynoldsRabinowitz et al. (2016) found that youth temperamental withdrawal interacted with neighborhood processes in predicting their risks for internalizing symptoms. Specifically, youth with high withdrawal manifested higher anxiety/depressive symptoms than youth with low withdrawal in the context of low neighborhood crime but not in the context of high neighborhood crime. Youth with high withdrawal also manifested greater internalizing symptoms in the context of low neighborhood social cohesion but not in the context of high neighborhood social cohesion.

Although the patterns of temperament-by-neighborhood interactions reported in the literature have been mixed, these findings have provided evidence that temperament plays a significant role in shaping children’s socialization experience in neighborhood and community contexts. Further supporting this perspective, Reference Zhao, Ettekal, Nickerson, Schuetze, Shisler, Godleski and EidenZhao et al. (2022) identified two longitudinal trajectories of child exposure to community violence (CECV) reflecting high exposure and low exposure to CECV, using an at-risk sample of primarily low-income families with high rates of prenatal substance exposure. Child temperament and maternal harshness interacted in predicting children’s CECV trajectories: Children with high activity levels and experiencing high maternal harshness in early childhood had the highest likelihood of being in the high exposure-increasing trajectory (Reference Zhao, Ettekal, Nickerson, Schuetze, Shisler, Godleski and EidenZhao et al., 2022). This study illustrates the value of examining multiple system levels simultaneously, demonstrating the relevance of interactions and transactions across temperament, parenting, or family system variables, and broader contexts.

5.2.5 Peers

Because temperament emotional reactivity and regulation play central roles in the quality of children’s relationships in general, it is not surprising that they impact children’s peer relationships both directly, as children engage with peers differently and evoke different responses from them, and indirectly through children’s social skills (Reference Sanson, Hemphill, Yagmurlu, McClowry, Smith and HartSanson et al., 2011). Social or peer competence is the ability to initiate and maintain effective interactions and relationships with peers, which promotes a sense of belonging (e.g., Reference Rubin, Bowker, Kennedy, Rubin, Bukowski and LaursenRubin et al., 2009) and has implications for children’s social, emotional, behavioral, and academic adjustment over time, including predicting peer problems, personality, and psychopathology into adolescence (e.g., Reference Baardstu, Coplan, Karevold, Laceulle and von SoestBaardstu et al., 2020; Reference RapeeRapee, 2014).

Children’s higher effortful control predicts better social competence (Reference Lengua, Kiff, Moran, Zalewski, Thompson, Cortes and RuberryLengua et al., 2014; Reference Zhou, Main and WangZhou et al., 2010) and lower externalizing and aggression (Reference Zhou, Main and WangZhou et al., 2010). In particular, inhibitory control and attention focusing are related to lower peer conflict, and attention focusing is related to higher sociability, better communication and assertiveness in peer interactions (Reference Acar, Rudasill, Molfese, Torquati and ProkaskyAcar et al., 2015), and higher social confidence (Reference Beceren and ÖzdemirBeceren & Özdemir, 2019) in preschool-age children. Children higher in effortful control are more likely to modulate an emotional reaction, delay an impulsive response, attend to relevant cues in the situation, and, as a result, engage in more effective efforts at initiating and maintaining interactions.

Conversely, children who are higher in negative emotionality (Reference Brumariu and KernsBrumariu & Kerns, 2013), and anger or frustration in particular (Reference Zhou, Main and WangZhou et al., 2010), tend to exhibit lower social or peer competence and higher externalizing problems, which interfere with positive peer relationships. These children react more strongly and negatively during peer interactions, particularly during disagreements or conflicts, provoking negative reactions from peers and rupturing relationships. Furthermore, a bidirectional process contributes to the development of peer problems such that being higher in negative emotionality lowers peer status, which in turn increases negative emotionality (Reference Bengtsson, Arvidsson and NyströmBengtsson et al., 2022). One mechanism that accounts for this reciprocal association is an increased tendency to perceive and expect rejection from peers (Reference Araiza, Freitas and KleinAraiza et al., 2020). Children higher in negative emotionality and lower in regulation are more likely to be rejected by peers (Reference Ato, Fernández-Vilar and GaliánAto et al., 2020). In addition, children higher in anxiety–withdrawal and anger–aggression are also more likely to experience peer victimization, particularly if they are immigrants (Reference Pistella, Zava, Sette, Baumgartner and BaioccoPistella et al., 2020). Child inhibition or fearfulness also impacts peer relationships. For example, highly inhibited or risk-averse preschool-age children aged three to five are less socially integrated and less dominant than children who are average or highly exuberant or risk seeking, but they are not more likely to be rejected by peers (Reference Tarullo, Mliner and GunnarTarullo et al. 2011). In contrast, highly exuberant children are more dominant, more often exhibit anger, and have more conflictual relationships (Reference Tarullo, Mliner and GunnarTarullo et al., 2011).

Surgency, which is related to exuberance, also contributes to peer relationships. Surgency combines positive affect and impulsivity with low shyness and withdrawal, all behaviors that play a role in peer interactions. Whereas low-surgent children are likely to be shy and socially withdrawn (e.g., Reference Rubin, Bowker, Kennedy, Rubin, Bukowski and LaursenRubin et al., 2009), high-surgent children are likely to be socially engaged and outgoing (Reference Rubin, Coplan, Fox and CalkinsRubin et al., 1995) but are also likely to develop externalizing problems (Reference Stifter, Putnam and JahromiStifter et al., 2008) and be rejected by peers (e.g., Reference Gunnar, Sebanc, Tout, Donzella and van DulmenGunnar et al., 2003). Examining children’s surgency as they were entering grade school at 6–7 years of age, one study found that children high in surgency developed more negative peer-related behaviors, including initiating and maintaining negative interactions, whereas children low in surgency demonstrated more wariness with peers (Reference Dollar and StifterDollar & Stifter, 2012).

It appears that these associations depend on other moderating factors, such as children’s self-regulation or emotion-regulation capacities as well as the presence of supportive adults. Negative emotionality and effortful control interact in predicting social competence and peer relationship quality, with effortful control modulating the effects of emotionality (Reference Eisenberg, Fabes, Guthrie, Reiser, Pulkkinen and CaspiEisenberg et al., 2002). Similar patterns of association have been found in relation to aspects of social and peer competence. For example, moderate to high levels of self-regulation predict successful social functioning, particularly for children who are also high in negative emotionality (Reference Eisenberg, Fabes, Guthrie, Reiser, Pulkkinen and CaspiEisenberg et al., 2002). Attention focusing moderates the association between shyness and peer communication skills such that high shyness is related to poor communication only for children low in attention focusing. Low shyness is related to high peer conflict, but again only for children low in attention focusing (Reference Acar, Rudasill, Molfese, Torquati and ProkaskyAcar et al., 2015).

Children’s peer relationships most often occur in school or in other social contexts, and their relationships with parents, teachers, and other adults, such as coaches, appear to moderate associations of emotionality and self-regulation with peer relationships. For example, when children high in surgency also demonstrate support-seeking during a challenging task, they were rated as lower in aggression compared to those not seeing support (Reference Dollar and StifterDollar & Stifter, 2012). In addition, parenting moderates the relation of fear or inhibition in early childhood to later peer withdrawal, with sensitive or less overcontrolling parenting mitigating the association (Reference Sanson, Hemphill, Yagmurlu, McClowry, Smith and HartSanson et al., 2011). Similarly, the interaction between parenting and difficult temperament predicts social competence, such that when parental emotional and autonomy support are low, children with difficult temperament are rated by teachers as having lower social competence, but not when parenting quality is high (Reference Straight, Gallagher and KelleyStraight et al., 2008).

The quality of the relationship between teachers and children moderates and mediates the relations of temperament with peer interactions (Reference Rudasill, Niehaus, Buhs and WhiteRudasill et al., 2013). One study found that children’s difficult temperament was related to less close relationships and more conflict with teachers. Teacher–child closeness was positively related to children’s prosocial behaviors, and teacher–child conflict was related to high levels of aggression, victimization, and fewer prosocial interactions, with teacher–child conflict mediating the association between difficult temperament and peer behaviors (Reference Rudasill, Niehaus, Buhs and WhiteRudasill et al., 2013). Another study found that teacher sensitivity and responsiveness in first grade, with children aged 6–7, moderated the association of infant temperament with children’s first-grade peer relationships. Having a sensitive teacher buffered the disruptive effects of low approach, adaptability, and high negative affect on peer interactions (Reference Frohn, Acar, Rudasill, Buhs and Pérez-GonzálezFrohn et al., 2021).

5.2.6 School and Academics

Peer relationships and teacher–child relationships are key pathways through which temperament shapes children’s academic achievement and school adaptation. In addition, researchers have examined children’s classroom engagement, liking school, and learning-related behaviors (e.g., study skills) as mediators in relations between temperament and academic achievement. For example, using a school-based sample of 2nd to 6th graders aged 6–12 years in Spain, Reference Sánchez-Pérez, Fuentes, Eisenberg and González-SalinasSánchez-Pérrez et al. (2018) found that children with high effortful control had better study skills, which in turn were associated with higher academic achievement and positive social adaptations at school. Furthermore, Reference Valiente, Swanson and Lemery‐ChalfantValiente et al. (2012) found that kindergartners in the United States who were high on temperamental shyness, anger, or impulsivity and low on effortful control displayed lower school liking and classroom participation, but effortful control buffered children from the deleterious effects of impulsivity and anger on school-related outcomes. In addition, researchers have found bidirectional relations between temperament and academic achievement. For example, effortful control shows bidirectional and positive relations with children’s math achievement in school-aged children 5–9 years old from Chinese-American immigrant families (Reference Mauer, Zhou and UchikoshiMauer et al., 2021). Together, these studies highlight the complex pathways through which temperament shapes children’s learning experience and adaptations in the school context.

5.3.1 Change in Temperament

Brain development that occurs during adolescence implies that both reactivity and regulatory components of temperament change during this period (Reference Caspi, Roberts and ShinerCaspi et al., 2005). Facets of positive emotional reactivity increase during adolescence, with evidence of increases in behavioral approach, reward sensitivity, and high intensity pleasure (e.g., Reference Colder, Hawk, Lengua, Wiezcorek, Eiden and ReadColder et al., 2013; Reference Pagliaccio, Luking, Anokhin, Gotlib, Hayden, Olino and … & BarchPagliaccio et al., 2016; Reference Zohar, Zwir, Wang, Cloninger and AnokhinZohar et al., 2019). Conversely, negative emotional reactivity appears to decline during adolescence, although the literature is limited. Reference Colder, Hawk, Lengua, Wiezcorek, Eiden and ReadColder et al (2013) found that sensitivity to punishment, assessed using a laboratory task, declined from early to middle adolescence. This is consistent with evidence that parent-reported fear, frustration, and shyness declined in early to middle adolescence (Reference Laceulle, Nederhof, Karreman, Ormel and van AkenLaceulle et al., 2012) and that self-reported sensitivity to punishment declined during middle adolescence (Reference Balle, Fiol-Veny, de la Torre-Luque, Llabres and BornasBalle et al., 2022).

Effortful control is expected to improve during adolescence as neural structures supporting cognitive control mature; however, this may depend on the specific dimensions assessed and on the measurement method. Reference Ferguson, Brunsdon and BradfordFerguson et al. (2021) found that task-assessed planning ability, working memory, and inhibitory control improved during adolescence, but measures of cognitive flexibility did not change. Reference Fosco, Hawk, Colder, Meisel and LenguaFosco et al. (2019) used a laboratory task and parent-report questionnaire to assess inhibitory control and, consistent with Reference Ferguson, Brunsdon and BradfordFergusson et al. (2021), found that task-assessed inhibitory control improved from early to middle adolescence. However, no change was evident for parent-reported inhibitory control. Impulsivity is often construed as an aspect of effortful control. However, it is a heterogenous construct that also often includes reward reactivity and approach motivation (Reference Dawe, Gullo and LoxtonDawe et al., 2004). Impulsivity seems to increase during early adolescence, with a peak around age fifteen, and then it declines (Reference Quinn and HardenQuin & Harden, 2013; Reference Shulman, Harden, Chein and SteinbergShulman et al., 2015). These patterns might suggest that cognitive control is initially overwhelmed by rapid development in reward reactivity and approach motivation, and that with maturity of relevant neural structures adolescents are better able to modulate positive emotional reactivity.

5.3.2 Psychopathology and Substance Use

Vulnerability models suggest that temperament can increase risk for poor adjustment and psychopathology (Reference De Bolle, Beyers, De Clercq and De FruytDe Bolle et al., 2012). Poor effortful control and high negative emotional reactivity are cross-sectionally and prospectively associated with adolescent internalizing symptoms (Reference Colder and O’ConnorColder & O’Connor, 2004; Reference de la Torre-Luque, Fiol-Veny, Balle, Nelemans and Bornasde la Torre-Luque et al., 2020; Reference Hoffmann, Pan, Manfro, de Jesus Mari, Miguel, Bressan and … & SalumHoffmann et al., 2019; Reference Snyder, Gulley, Bijttebier, Hartman, Oldehinkel, Mezulis and … & HankinSnyder et al., 2015). Reference Lawson, Kellerman, Kleiman, Bleidorn, Hopwood and RobinsLawson et al. (2022) found that high levels of effortful control decreased the probability of adolescents experiencing the onset of suicidal ideation, plans, and attempts (a cluster of symptoms associated with depression), whereas high levels of negative emotional reactivity increased the probability of experiencing the onset of these symptoms. Poor effortful control and high positive emotional reactivity are associated with externalizing symptoms, including substance use (Reference Colder and O’ConnorColder & O’Connor, 2004; Reference Colder, Hawk, Lengua, Wiezcorek, Eiden and ReadColder et al., 2013; Reference Fosco, Hawk, Colder, Meisel and LenguaFosco et al., 2019; Reference Hoffmann, Pan, Manfro, de Jesus Mari, Miguel, Bressan and … & SalumHoffmann et al., 2019; Reference Snyder, Gulley, Bijttebier, Hartman, Oldehinkel, Mezulis and … & HankinSnyder et al., 2015).

In a seven-year longitudinal study that spanned the ages 12–19 years, Reference Dolcini-Catania, Byrne, Whittle, Schwartz, Simmons and AllenDolcini-Catania et al. (2020) tested a mediational model whereby temperament at age twelve predicted mental health symptoms in early adolescence, which in turn predicted major depressive symptoms in late adolescence. Low surgency, high negative emotional reactivity, and low effortful control predicted internalizing, which in turn predicted symptoms of major depression. There was also support for an externalizing pathway that involved low effortful control that predicted externalizing problems, which in turn predicted symptoms of major depression. This study is notable because it suggests a cascading effect of temperament that increases vulnerability for psychopathology many years later and demonstrates that temperament impacts adjustment through multiple complex pathways consistent with the idea of equifinality (multiple pathways can lead to the same outcome).

Temperament is also related to health outcomes in adolescence. For example, Reference Nelson, Byrne, Simmons, Whittle, Schwartz, O’Brien-Simpson and AllenNelson et al. (2018) examined the association of adolescent temperament with C-reactive protein (CRP), which is believed to index inflammation and immune system functioning. This is of interest because high levels of CRP are linked to poor physical and mental health. Findings suggested that effortful control was associated with low levels of CRP, whereas negative emotional reactivity was associated with high levels of CRP. Reference Brody, Yu, Miller and ChenBrody et al. (2023) similarly found that high levels of negative emotional reactivity and poor attentional control in adolescence were associated with worsening inflammation in young adulthood. These studies suggest a potential biological pathway whereby immune functioning as measured by indicators of inflammation may mediate links between temperament and mental and physical health outcomes.

An intriguing model that might account for linkages between temperament and adjustment is the scar model, initially proposed by Reference Lewinsohn, Steinmetz, Larson and FranklinLewinsohn and colleagues (1981). The model posits that experiencing intense psychopathology symptoms leaves a lasting impact on temperament, which could manifest as temporary (i.e., scab effect) (Reference Li and ZinbargLi & Zinbarg, 2007) or long-lasting (i.e., scar effect) changes in temperament. Along with the vulnerability model, this suggests potential reciprocal associations between temperament and adjustment. In one of the few tests of this idea with a longitudinal adolescent sample, Reference Ramer, Perhamus and ColderRamer et al. (2024) found that sensitivity to reward was reciprocally associated with oppositional defiant symptoms in early and middle adolescence, such that high sensitivity to reward predicted subsequent oppositional defiant symptoms (vulnerability) and high levels of oppositional defiant symptoms predicted subsequent sensitivity to reward (scar).

Temperament influences learning, including the degree to which positive and negative reinforcement and punishment shape behavior (Reference Shiner, Caspi, Zentner and ShinerShiner & Caspi, 2012), and temperament differences elicit different reactions from the environment (Reference Bates, Schermerhorn, Petersen, Lewis and RudolphBates et al., 2014). Hence, linkages between temperament and adjustment likely depend on features of the environment. In their review, Reference Rioux, Castellanos-Ryan, Parent and SéguinRioux et al. (2016) concluded that there was consistent evidence that high levels of substance use and externalizing behaviors in adolescence were most evident when more adverse family environments were combined with an “adventuresome temperament” (a combination of activity level and reward motivation, and low levels of effortful control, negative affect, fearfulness, and shyness). Poor regulation and strong emotional reactivity seem to leave children vulnerable to the effects of adverse family environments. Using a large longitudinal sample, Reference Kapetanovic, Zietz, Lansford, Bacchini, Bornstein, Chang and Al-HassanKapetanovic et al. (2023) found evidence for moderated mediational pathways predicting adolescent substance use. Positive parenting and harsh discipline were associated with adolescent substance use indirectly through sensation-seeking, and these indirect effects were moderated by adolescent temperament. The authors concluded that the study provided evidence for differential susceptibility, such that a temperament characteristic could be a liability in one parenting and family context, but protective in another. For example, poor activation control was a liability for adolescents in the context of low positive parental practices, but these adolescents were more resilient to harsh discipline.

5.3.3 Peer and Romantic Relationships

As noted, peer relationships become increasingly important in adolescence, and successful adaptation in this domain has both short- and long-term implications for a variety of psychosocial outcomes. There is evidence that temperament plays an important role in social adaptation in adolescents. Adolescent effortful control is associated with social competence, and this association is partly mediated by empathy and perspective-taking (Reference Zorza, Marino, Lemus and MesasZorza et al., 2013; Reference Murphy, Shepard, Eisenberg, Fabes and GuthrieMurphy et al., 1999, Reference Murphy, Shepard, Eisenberg and Fabes2004). A small number of studies have considered the role of temperament in youth that affiliate with deviant peers who support and encourage problem behavior. Findings suggest that poor effortful control, high intensity pleasure (an aspect of positive emotional reactivity related to novelty/sensation-seeking), and negative emotional reactivity influence selection into deviant peer groups and friendships, which in turn predict engagement in substance use and antisocial behavior (e.g., Reference Clark, Durbin, Heitzeg, Iacono, McGue and HicksClark et al., 2023; Reference Creemers, Dijkstra, Vollebergh, Ormel, Verhulst and HuizinkCreemers et al., 2010). Temperament is also likely to influence selection into prosocial peer groups and friendships, but this has been less studied and remains an important direction for future research.

Temperament might also moderate the influence of peers on adjustment outcomes. For example, affiliating with peers engaging in deviant behavior is strongly associated with antisocial behavior such as delinquency and aggression, and this relationship is particularly strong for youth characterized by poor effortful control (Reference Mrug, Molina, Hoza, Gerdes, Hinshaw, Hechtman and ArnoldMrug et al., 2012). Reference Scalco, Evans and ColderScalco et al. (2021) found that high surgency and low effortful control in conjunction with peer alcohol use were associated with heavy drinking in middle adolescence, which in turn was associated with alcohol-use disorder symptoms in late adolescence. Reference Scalco and ColderScalco and Colder (2017) found that perceived peer norms about alcohol and drug use were most strongly associated with increases in cannabis use among youth who were high in surgency. One study considered internalizing symptoms and found that peer rejection was associated with increases in adolescent depression, and this association was strongest at high levels of negative emotional reactivity (Reference Brendgen, Wanner, Morin and VitaroBrengden et al., 2005). Overall, these studies suggest that temperament leaves some youth particularly vulnerable to negative peer contexts.

Romantic relationships represent a domain of peer relationships that first emerge in adolescence. A small number of studies have found that temperament influences the nature and quality of adolescent romantic relationships. For example, poor effortful control in early adolescence is associated with bullying perpetration, which in turn predicted having many dating partners and dating aggression in late adolescence (Reference Farrell and VaillancourtFarrell & Vaillencourt, 2019). Low effortful control and high negative emotional reactivity at age seventeen was associated with problematic romantic relationships in young adulthood (Reference Samek, Hicks, Iacono and McGueSemak et al., 2020). Given that early romantic relationships help set the stage for adult romantic relationships, additional studies that consider adolescent temperament would be an important direction for research, including studies that consider the potential mechanisms of these associations.

5.3.4 Neighborhood

Neighborhoods influence child adjustment, and as youth enter adolescence they may be more susceptible to neighborhood contexts, as they are likely to venture out without adult supervision. Several studies have considered temperament within the neighborhood context. A large literature suggests that neighborhood disadvantage (neighborhoods characterized by poverty, low social cohesion, and danger) is associated with adolescent externalizing behavior and internalizing behavior. Reference Trentacosta, Hyde, Shaw and CheongTrentacosta et al. (2009) considered the moderating effect of sensation-seeking in a sample of boys and found that neighborhood danger was associated with adolescent externalizing symptoms at high levels of sensation-seeking (referred to as “daring” by the authors). Reference Andreas and WatsonAndreas and Watson (2016) similarly found that neighborhood disadvantage was associated with increased drug use for adolescents high in sensation-seeking (also see Reference Neumann, Barker, Koot and MaughanNeumann et al., 2010). In one of the few studies of neighborhood to consider temperament and internalizing symptoms, Reference Rabinowitz, Drabick and ReynoldsRabinowitz et al. (2016) found that behavioral withdrawal (an individual difference that overlaps with behavioral inhibition and negative emotional reactivity) was associated with internalizing symptoms for youth living in neighborhoods characterized by low social cohesion. Overall, these studies support the idea of a diathesis–stress model wherein temperament leaves some youth particularly vulnerable to risky contexts, but the number of studies is relatively few.