Unique neurobiology during the sensitive period for attachment produces distinctive infant trauma processing

Reconsidering the nature of threat in infancy: Integrating animal and human studies on neurobiological effects of infant stress

Early life stress has been associated with elevated risk for later psychopathology. One mechanism that may contribute to such long-term risk is alterations in amygdala development, a brain region critical to stress responsivity. Yet effects of stress on the amygdala during human infancy, a period of particularly rapid brain development, remain largely unstudied. In order to model how early stressors may affect infant amygdala development, several discrepancies across the existing literatures on early life stress among rodents and early threat versus deprivation among older human children and adults need to be reconciled. We briefly review the key findings of each of these literatures. We then consider them in light of emerging findings from studies of human infants regarding relations among maternal caregiving, infant cortisol response, and infant amygdala volume. Finally, we advance a developmental salience model of how early threat may impact the rapidly developing infant brain, a model with the potential to integrate across these divergent literatures. Future work to assess the value of this model is also proposed.

Linking maternal disrupted interaction and infant limbic volumes: The role of infant cortisol output

Despite a large animal literature documenting the role of low maternal nurturance and elevated glucocorticoid production on offspring limbic development, these pathways have not yet been assessed during human infancy. Informed by animal models, the present study examined whether 1) maternal disrupted interaction is related to infant cortisol levels, 2) infant cortisol levels are associated with infant limbic volumes, and 3) infant cortisol levels mediate associations between maternal disrupted interaction and infant limbic volumes. Participants included 57 mother-infant dyads. Infant saliva was measured at one time point before and two time points after the Still-Face Paradigm (SFP) at age 4 months. Five aspects of maternal disrupted interaction were coded during the SFP reunion episode. Between 4 and 25 months (M age = 11.74 months, SD = 6.12), under natural sleep, infants completed an MRI. Amygdala and hippocampal volumes were calculated via automated segmentation. Results indicated that 1) maternal disrupted interaction, and specifically disoriented interaction, with the infant was associated with higher infant salivary cortisol (AUCg) levels during the SFP, 2) higher infant AUCg was related to enlarged bilateral amygdala and hippocampal volumes, and 3) infant AUCg mediated the relation between maternal disrupted interaction and infant amygdala and hippocampal volumes. Findings are consistent with controlled animal studies and provide evidence of a link between increased cortisol levels and enlarged limbic volumes in human infants. Results further suggest that established interventions to decrease maternal disrupted interaction could impact both infant cortisol levels and infant limbic volumes.

Maternal Childhood Abuse Versus Neglect Associated with Differential Patterns of Infant Brain Development

Severity of maternal childhood maltreatment has been associated with lower infant grey matter volume and amygdala volume during the first two years of life. A developing literature argues that effects of threat (abuse) and of deprivation (neglect) should be assessed separately because these distinct aspects of adversity may have different impacts on developmental outcomes. However, distinct effects of threat versus deprivation have not been assessed in relation to intergenerational effects of child maltreatment. The objective of this study was to separately assess the links of maternal childhood abuse and neglect with infant grey matter volume (GMV), white matter volume (WMV), amygdala and hippocampal volume. Participants included 57 mother-infant dyads. Mothers were assessed for childhood abuse and neglect using the Adverse Childhood Experiences (ACE) questionnaire in a sample enriched for childhood maltreatment. Between 4 and 24 months (M age = 12.28 months, SD = 5.99), under natural sleep, infants completed an MRI using a 3.0 T Siemens scanner. GMV, WMV, amygdala and hippocampal volumes were extracted via automated segmentation. Maternal history of neglect, but not abuse, was associated with lower infant GMV. Maternal history of abuse, but not neglect, interacted with age such that abuse was associated with smaller infant amygdala volume at older ages. Results are consistent with a threat versus deprivation framework, in which threat impacts limbic regions central to the stress response, whereas deprivation impacts areas more central to cognitive function. Further studies are needed to identify mechanisms contributing to these differential intergenerational associations of threat versus deprivation.

The impact of adversities across the lifespan on psychological symptom profiles in late adulthood: a latent profile analysis

People commonly face adverse circumstances throughout life, which increases risk for psychiatric disorders, such as anxiety, depression, psychosis, and posttraumatic stress disorder (PTSD). Adversities may occur during different periods in life. Especially adversity during early periods has been suggested to put individuals at risk for adverse mental health outcomes. Here, we investigated whether timing of adversity during the prenatal period, childhood, or mid-to-late adulthood differentially impacted classification into late adulthood symptom profiles. We performed sex-stratified Latent Profile Analysis to identify latent profiles regarding anxious, depressive, psychotic, and PTSD symptoms in n = 568 Dutch famine birth cohort members (n = 294 women, n = 274 men, mean age(SD) = 72.9(0.8)). Cross-sectional late adulthood symptomatology, childhood traumatic maltreatment, and adulthood trauma were based on self-report questionnaires. Prenatal adversity was considered present when individuals were prenatally exposed to the 1944-45 Dutch famine. In both men and women we identified one anxious/depressive profile and three profiles with approximately equal severity of all symptom types within each profile, yet differentiating in overall severity (low, mild, high) between profiles. We additionally found a PTSD symptom profile in women. In men, logistic regression models showed significant associations between prenatal, childhood and adulthood adversity, and profile classification, with differential effects depending on timing and most profound effects of child maltreatment. In women, childhood and adulthood adversity significantly increased classification probability into almost all profiles, with no significant effect of prenatal adversity. These findings support a time-dependent and sex-specific impact of adversity during different periods across the lifespan on psychological health, with consequences into late adulthood.

Early life adversity affecting the attachment bond alters ventral tegmental area transcriptomic patterning and behavior almost exclusively in female mice

Early life experiences that affect the attachment bond formation can alter developmental trajectories and result in pathological outcomes in a sex-related manner. However, the molecular basis of sex differences is quite unknown. The dopaminergic system originating from the ventral tegmental area has been proposed to be a key mediator of this process. Here we exploited a murine model of early adversity (Repeated Cross Fostering, RCF) to test how interfering with the attachment bond formation affects the VTA-related functions in a sex-specific manner. Through a comprehensive behavioral screening, within the NiH RDoC framework, and by next-generation RNA-Seq experiments, we analyzed the long-lasting effect of RCF on behavioral and transcriptional profiles related to the VTA, across two different inbred strains of mouse in both sexes. We found that RCF impacted to an extremely greater extent VTA-related behaviors in females than in males and this result mirrored the transcriptional alterations in the VTA that were almost exclusively observed in females. The sexual dimorphism was conserved across two different inbred strains in spite of their divergent long lasting consequences of RCF exposure. Our data suggest that to be female primes a sub-set of genes to respond to early environmental perturbations. This is, to the best of our knowledge, the first evidence of an almost exclusive effect of early life experiences on females, thus mirroring the extremely stronger impact of precocious aversive events reported in clinical studies in women.

How Our Caregivers Shape Who We Are: The Seven Dimensions of Attachment at the Core of Personality

Psychology defines personality as the stable traits of an individual, and cognitive research suggests that a set of core beliefs is at the root of these traits. From this perspective, two major questions remain unanswered: (1) What are the core beliefs that make up personality? (2) How are they acquired? An interesting answer is provided by attachment theory, according to which attachment is at the basis of personality. The current theoretical formulation, however, does not sufficiently clarify the relationship between the two. Adopting a cognitive-clinical approach, we put forward a novel version of attachment theory, arguing that it can better account for the relationship between attachment and personality, thereby providing more convincing answers to questions (1) and (2). In particular, we propose that: (A) attachment information is acquired over seven dimensions; (B) the acquisition of each dimension is induced by a specific caregiving feature and (C) realized through a specific acquisition mechanism - imprinting. In a nutshell, we propose an Attachment-Personality Model (APM) according to which seven attachment dimensions constitute the knowledge core of personality. We finally discuss the significant implications of the model, especially its clinical application in terms of conception, assessment, and treatment of mental disorders. The model can be empirically tested, and we suggest three ways to do that.

Elevated infant cortisol is necessary but not sufficient for transmission of environmental risk to infant social development: Cross-species evidence of mother-infant physiological social transmission

Environmental adversity increases child susceptibility to disrupted developmental outcomes, but the mechanisms by which adversity can shape development remain unclear. A translational cross-species approach was used to examine stress-mediated pathways by which poverty-related adversity can influence infant social development. Findings from a longitudinal sample of low-income mother-infant dyads indicated that infant cortisol (CORT) on its own did not mediate relations between early-life scarcity-adversity exposure and later infant behavior in a mother-child interaction task. However, maternal CORT through infant CORT served as a mediating pathway, even when controlling for parenting behavior. Findings using a rodent "scarcity-adversity" model indicated that pharmacologically blocking pup corticosterone (CORT, rodent equivalent to cortisol) in the presence of a stressed mother causally prevented social transmission of scarcity-adversity effects on pup social behavior. Furthermore, pharmacologically increasing pup CORT without the mother present was not sufficient to disrupt pup social behavior. Integration of our cross-species results suggests that elevated infant CORT may be necessary, but without elevated caregiver CORT, may not be sufficient in mediating the effects of environmental adversity on development. These findings underscore the importance of considering infant stress physiology in relation to the broader social context, including caregiver stress physiology, in research and interventional efforts.

Defining Immediate Effects of Sensitive Periods on Infant Neurobehavioral Function

During a sensitive period associated with attachment, the infant brain has unique circuitry that enables the specialized adaptive behaviors required for survival in infancy. This infant brain is not an immature version of the adult brain. Within the attachment relationship, the infant remains close (proximity seeking) to the caregiver for nurturing and survival needs, but the caregiver also provides the immature infant with the physiological regulation interaction needed before self-regulation matures. Here we provide examples from the human and animal literature that illustrate some of these regulatory functions during sensitive periods, recent advances demonstrating the supporting transient neural mechanisms, and how these systems go awry in the absence of species-expected caregiving.

Observed Progression of Parents' Understanding of Preterm Infants' Behavioral Signs at 33 to 35 Weeks Corrected Age

BACKGROUND

Interventions aimed at improving parental understanding of preterm infants' behavioral signs have drawn increased attention in recent years. However, there are limited data regarding parents' actual perceptions of infants' behavior during parent-infant interactions while infants are in a light-sleep state.

PURPOSES

(1) To describe parental perceptions of infants' behavior at 33 to 35 weeks' corrected age during light-sleep and (2) to identify changes in parental perceptions of preterm infants' behavior over time.

METHODS

This study used a qualitative, longitudinal design based on observations and interviews. Three sets of parents and their infants born between 29 and 30 weeks' gestational age were observed up to 3 times during light sleep states when the infants were 33 to 35 weeks' corrected age. Parents were interviewed regarding their perceptions of infant behavior/growth once at the time of observation and once more within 2 weeks of the final observation. The findings are based on the observation of parents' perception-driven interactions with infants.

RESULTS

Four themes emerged describing the transition of parental perception that progresses to gain a better understanding of their infant's behavior through repeated interaction.

IMPLICATIONS FOR PRACTICE

The findings of this study inform caregivers in neonatal intensive care units regarding the unique experience of parent-infant dyads. This knowledge can help promote family-centered developmental care efforts in neonatal intensive care units.

IMPLICATIONS FOR RESEARCH

Further research should focus on studying a larger sample group to confirm the findings and refining strategies to incorporate the findings to enhance neonatal intensive care unit care.

An Animal Model for Mammalian Attachment: Infant Titi Monkey (Plecturocebus cupreus) Attachment Behavior Is Associated With Their Social Behavior as Adults

Close social bonds are integral for good health and longevity in humans and non-human primates (NHPs), yet we have very little understanding of the neurobiological differences between healthy and unhealthy relationships. Our current understanding of social bonding is grounded in Bowlby’s theory of attachment. Work done with human infants and adult couples has suggested that attachment behavior developed in infancy remains stable through development into adulthood. Unfortunately, knowledge of the neurobiological correlates of attachment behavior has been limited due to a lack of animal models with both infant and adult attachments similar to humans. To address this, we measured behavioral responses to separation from their primary attachment figure in infant and adult titi monkeys (Plecturocebus cupreus). In Experiment 1, we tested for a linear relationship between the subject’s response to separation as an infant and their response to separation as an adult. We found greater decreases in infant locomotor behavior in the presence, as opposed to absence, of their primary attachment figure to be indicative of decreased anxiety-like behavior in the presence, as opposed to absence, of their adult pair mates during a novelty response task. In Experiment 2, we increased our sample size, accounted for adverse early experience, and tested a different outcome measure, adult affiliative behavior. We hypothesized that the level of intensity of an infant’s response to separation would explain affiliative behavior with their mate as an adult, but adverse early experience could change this relationship. When we compared infant response to separation to adult affiliative behavior during the first 6 months of their first adult pair bond, we observed a linear relationship for infants with typical early experience, but not for infants with adverse early experience. Infants with a greater change in locomotive behavior between the father and alone conditions were more affiliative with their first adult pair mate. These data support the use of titi monkeys as an appropriate animal model for further investigation of the neurobiology underlying attachment behavior.

Attachment insecurity accounts for the relationship between maternal and paternal maltreatment and adolescent health

OBJECTIVES

Maltreatment is linked with poor health outcomes. Attachment and affect regulation may mitigate the long-term impact of these adverse experiences on health outcomes. Little is known about the relative impact of maternal versus paternal maltreatment and interparental violence (IPV) on general health status of female and male youth.

METHOD

The present study examined the impact of exposure to maternal and paternal emotional and physical maltreatment, neglect, IPV, and cumulative maltreatment exposure in adolescence on general physical health problems reported five years later. High-risk youth (N = 179; Mage = 15.34, SD = 1.53; 46.4% female) self-reported maltreatment experiences, attachment insecurity, and affect dysregulation at Time 1; and affect dysregulation and physical health five years later at Time 2.

RESULTS

Attachment insecurity accounted for the effect of maternal and paternal emotional maltreatment, and maternal and paternal cumulative maltreatment exposure, on physical health. Additionally, attachment insecurity accounted for the effect of paternal neglect on physical health. Further sex differences were found with regard to maltreatment type and are discussed.

CONCLUSION

Both maternal and paternal maltreatment in adolescence predicted poor general health five years later via attachment insecurity. Youth who lack a secure attachment with their parents are most vulnerable to these impacts.

Development of Threat Expression Following Infant Maltreatment: Infant and Adult Enhancement but Adolescent Attenuation

Early life maltreatment by the caregiver constitutes a major risk factor for the development of later-life psychopathologies, including fear-related pathologies. Here, we used an animal model of early life maltreatment induced by the Scarcity-Adversity Model of low bedding (LB) where the mother is given insufficient bedding for nest building while rat pups were postnatal days (PN) 8-12. To assess effects of maltreatment on the expression of threat-elicited defensive behaviors, animals underwent odor-shock threat conditioning at three developmental stages: late infancy (PN18), adolescence (PN45) or adulthood (>PN75) and tested the next day with odor only presentations (cue test). Results showed that in typically developing rats, the response to threat increases with maturation, although experience with maltreatment in early infancy produced enhanced responding to threat in infancy and adulthood, but a decrease in maltreated adolescents. To better understand the unique features of this decreased threat responding in adolescence, c-Fos expression was assessed within the amygdala and ventromedial prefrontal cortex (vmPFC) associated with the cued expression of threat learning. Fos counts across amygdala subregions were lower in LB rats compared to controls, while enhanced c-Fos expression was observed in the vmPFC prelimbic cortex (PL). Correlational analysis between freezing behavior and Fos revealed freezing levels were correlated with CeA in controls, although more global correlations were detected in LB-reared rats, including the BA, LA, and CeA. Functional connectivity analysis between brain regions showed that LB reared rats exhibited more diffuse interconnectivity across amygdala subnuclei, compared the more heterogeneous patterns observed in controls. In addition, functional connectivity between the IL and LA switched from positive to negative in abused adolescents. Overall, these results suggest that in adolescence, the unique developmental decrease in fear expression following trauma is associated with distinct changes in regional function and long-range connectivity, reminiscent of pathological brain function. These results suggest that early life maltreatment from the caregiver perturbs the developmental trajectory of threat-elicited behavior. Indeed, it is possible that this form of trauma, where the infant's safety signal or "safe haven" (the caregiver) is actually the source of the threat, produces distinct outcomes across development.

Infant Trauma Alters Social Buffering of Threat Learning: Emerging Role of Prefrontal Cortex in Preadolescence

Within the infant-caregiver attachment system, the primary caregiver holds potent reward value to the infant, exhibited by infants' strong preference for approach responses and proximity-seeking towards the mother. A less well-understood feature of the attachment figure is the caregiver's ability to reduce fear via social buffering, commonly associated with the notion of a "safe haven" in the developmental literature. Evidence suggests this infant system overlaps with the neural network supporting social buffering (attenuation) of fear in the adults of many species, a network known to involve the prefrontal cortex (PFC). Here, using odor-shock conditioning in young developing rats, we assessed when the infant system transitions to the adult-like PFC-dependent social buffering of threat system. Rat pups were odor-shock conditioned (0.55 mA-0.6 mA) at either postnatal day (PN18; dependent on mother) or 28 (newly independent, weaned at PN23). Within each age group, the mother was present or absent during conditioning, with PFC assessment following acquisition using 14C 2-DG autoradiography and cue testing the following day. Since the human literature suggests poor attachment attenuates the mother's ability to socially buffer the infants, half of the pups at each age were reared with an abusive mother from PN8-12. The results showed that for typical control rearing, the mother attenuated fear in both PN18 and PN28 pups, although the PFC [infralimbic (IL) and ventral prelimbic (vPL) cortices] was only engaged at PN28. Abuse rearing completely disrupted social buffering of pups by the mother at PN18. The results from PN28 pups showed that while the mother modulated learning in both control and abuse-reared pups, the behavioral and PFC effects were attenuated after maltreatment. Our data suggest that pups transition to the adult-like PFC social support circuit after independence from the mother (PN28), and this circuit remains functional after early-life trauma, although its effectiveness appears reduced. This is in sharp contrast to the effects of early life trauma during infancy, where social buffering of the infant is more robustly impacted. We suggest that the infant social buffering circuit is disengaged by early-life trauma, while the adolescent PFC-dependent social buffering circuit may use a safety signal with unreliable safety value.

Using a Developmental Ecology Framework to Align Fear Neurobiology Across Species

Children's development is largely dependent on caregiving; when caregiving is disrupted, children are at increased risk for numerous poor outcomes, in particular psychopathology. Therefore, determining how caregivers regulate children's affective neurobiology is essential for understanding psychopathology etiology and prevention. Much of the research on affective functioning uses fear learning to map maturation trajectories, with both rodent and human studies contributing knowledge. Nonetheless, as no standard framework exists through which to interpret developmental effects across species, research often remains siloed, thus contributing to the current therapeutic impasse. Here, we propose a developmental ecology framework that attempts to understand fear in the ecological context of the child: their relationship with their parent. By referring to developmental goals that are shared across species (to attach to, then, ultimately, separate from the parent), this framework provides a common grounding from which fear systems and their dysfunction can be understood, thus advancing research on psychopathologies and their treatment.

Psychobiology of Attachment and Trauma-Some General Remarks From a Clinical Perspective

Attachment refers to a psychobiological principle that is deeply rooted in evolutionary development; it is thought to contribute a major advantage in the survival of the social group. Within individual development it indicates a primary motivational system that guides the initial transactions between mother and baby and furthermore mediates affective attunement and regulation. Psychosocial learning, in close interaction with genetics and epigenetics, also develops a decisive foundation for further brain development of the infant. Finally, the attachment pattern established forms an enduring, relational context for later affective, cognitive, and social development of the child. As an unconsciously active matrix for future personal relationships it has a particular impact on the comprehensive psychological functions of empathy and mentalization. Early adverse and traumatic experiences or major emotional neglect may lead to different levels of security versus insecurity or disorientation-disorganization of the attachment pattern that corresponds to characteristic features of neurobiological regulation.

Early life adversity during the infant sensitive period for attachment: Programming of behavioral neurobiology of threat processing and social behavior

Animals, including humans, require a highly coordinated and flexible system of social behavior and threat evaluation. However, trauma can disrupt this system, with the amygdala implicated as a mediator of these impairments in behavior. Recent evidence has further highlighted the context of infant trauma as a critical variable in determining its immediate and enduring consequences, with trauma experienced from an attachment figure, such as occurs in cases of caregiver-child maltreatment, as particularly detrimental. This review focuses on the unique role of caregiver presence during early-life trauma in programming deficits in social behavior and threat processing. Using data primarily from rodent models, we describe the interaction between trauma and attachment during a sensitive period in early life, which highlights the role of the caregiver's presence in engagement of attachment brain circuitry and suppressing threat processing by the amygdala. These data suggest that trauma experienced directly from an abusive caregiver and trauma experienced in the presence of caregiver cues produce similar neurobehavioral deficits, which are unique from those resulting from trauma alone. We go on to integrate this information into social experience throughout the lifespan, including consequences for complex scenarios, such as dominance hierarchy formation and maintenance.