Widespread reductions in cortical thickness following severe early-life deprivation: a neurodevelopmental pathway to attention-deficit/hyperactivity disorder

Neurobiological Models of the Impact of Adversity on Education

Poverty and exposure to adversity have been linked with decreased educational success. Various environmental and neurobiological pathways have been proposed for these associations, however, existing models have several clear drawbacks. Here we outline existing models, and propose an alternate model linking exposure to adverse experiences in childhood to education success. Specifically, we propose that measured dimensions of experience (e.g., decreased cognitive enrichment or increased exposure to violence), instead of named exposures (e.g., poverty) impact neurobiology through neurodevelopmental processes of neuroplasticity. Our model results in testable hypotheses and clear intervention strategies. We predict that exposure to trauma will have a distinct neurobiological impact from exposure to a lack of cognitive stimulation and that these distinct exposures will benefit from different interventions. Specificity in this arena is thus likely to better support educational achievement for disadvantaged children.

Childhood abuse and deprivation are associated with distinct sex-dependent differences in brain morphology

Childhood adversity (CA) has been associated with long-term structural brain alterations and an increased risk for psychiatric disorders. Evidence is emerging that subtypes of CA, varying in the dimensions of threat and deprivation, lead to distinct neural and behavioral outcomes. However, these specific associations have yet to be established without potential confounders such as psychopathology. Moreover, differences in neural development and psychopathology necessitate the exploration of sexual dimorphism. Young healthy adult subjects were selected based on history of CA from a large database to assess gray matter (GM) differences associated with specific subtypes of adversity. We compared voxel-based morphometry data of subjects reporting specific childhood exposure to abuse (n=127) or deprivation (n=126) and a similar sized group of controls (n=129) without reported CA. Subjects were matched on age, gender, and educational level. Differences between CA subtypes were found in the fusiform gyrus and middle occipital gyrus, where subjects with a history of deprivation showed reduced GM compared with subjects with a history of abuse. An interaction between sex and CA subtype was found. Women showed less GM in the visual posterior precuneal region after both subtypes of CA than controls. Men had less GM in the postcentral gyrus after childhood deprivation compared with abuse. Our results suggest that even in a healthy population, CA subtypes are related to specific alterations in brain structure, which are modulated by sex. These findings may help understand neurodevelopmental consequences related to CA.

Adolescent neurobiological susceptibility to social context

Adolescence has been characterized as a period of heightened sensitivity to social contexts. However, adolescents vary in how their social contexts affect them. According to neurobiological susceptibility models, endogenous, biological factors confer some individuals, relative to others, with greater susceptibility to environmental influences, whereby more susceptible individuals fare the best or worst of all individuals, depending on the environment encountered (e.g., high vs. low parental warmth). Until recently, research guided by these theoretical frameworks has not incorporated direct measures of brain structure or function to index this sensitivity. Drawing on prevailing models of adolescent neurodevelopment and a growing number of neuroimaging studies on the interrelations among social contexts, the brain, and developmental outcomes, we review research that supports the idea of adolescent neurobiological susceptibility to social context for understanding why and how adolescents differ in development and well-being. We propose that adolescent development is shaped by brain-based individual differences in sensitivity to social contexts - be they positive or negative - such as those created through relationships with parents/caregivers and peers. Ultimately, we recommend that future research measure brain function and structure to operationalize susceptibility factors that moderate the influence of social contexts on developmental outcomes.

The Association Between Socioeconomic Disadvantage and Attention Deficit/Hyperactivity Disorder (ADHD): A Systematic Review

This systematic review examines associations between parental socioeconomic disadvantage and childhood attention deficit/hyperactivity disorder (ADHD). Socioeconomic status (SES) was measured by parental income, education, occupation and marital status. Results were mixed by measure of SES with no one aspect being differentially related to ADHD. 42 studies were included in the review, of which 35 found a significant univariate association between socioeconomic disadvantage and ADHD. Meta-analyses of dimensions of SES and their association with ADHD indicate that children in families of low SES are on average 1.85-2.21 more likely to have ADHD than their peers in high SES families. In spite of substantial between-study heterogeneity, there is evidence for an association between socioeconomic disadvantage and risk of ADHD measured in different ways. This is likely mediated by factors linked to low SES such as parental mental health and maternal smoking during pregnancy.

Predictors and Correlates of Inattentive/Overactive Behaviors in Internationally Adopted Children

Children adopted internationally following deprived early care have an elevated risk for difficulties with inattention/overactivity (Kreppner et al., 2001 ). The current study sought to identify predictors of inattention/overactivity and child and adoptive family challenges that co-occur with inattention/overactivity difficulties in a sample of internationally adopted children. Forty-eight children (mean age at adoption = 57.98 months, SD = 47.7 months) were examined at 3 yearly assessments, which included semistructured interviews, parent ratings, and neuropsychological assessment with children. Results revealed that older age at adoption, longer time in the adoptive home, and smaller family size were associated with greater parent-rated difficulties with inattention/overactivity. Additionally, greater inattention/overactivity difficulties were associated with poorer expressive language and reading performance, poorer child emotional-behavioral outcomes, and poorer adoptive family functioning. Given the increase in difficulties over time in the adoptive home, longer-term follow-up may be helpful to ensure appropriate intervention. Additionally, interventions may need to be more comprehensive given the connection between inattentive/overactive behaviors and other areas of functioning.

Annual Research Review: Enduring neurobiological effects of childhood abuse and neglect

BACKGROUND

Childhood maltreatment is the most important preventable cause of psychopathology accounting for about 45% of the population attributable risk for childhood onset psychiatric disorders. A key breakthrough has been the discovery that maltreatment alters trajectories of brain development.

METHODS

This review aims to synthesize neuroimaging findings in children who experienced caregiver neglect as well as from studies in children, adolescents and adults who experienced physical, sexual and emotional abuse. In doing so, we provide preliminary answers to questions regarding the importance of type and timing of exposure, gender differences, reversibility and the relationship between brain changes and psychopathology. We also discuss whether these changes represent adaptive modifications or stress-induced damage.

RESULTS

Parental verbal abuse, witnessing domestic violence and sexual abuse appear to specifically target brain regions (auditory, visual and somatosensory cortex) and pathways that process and convey the aversive experience. Maltreatment is associated with reliable morphological alterations in anterior cingulate, dorsal lateral prefrontal and orbitofrontal cortex, corpus callosum and adult hippocampus, and with enhanced amygdala response to emotional faces and diminished striatal response to anticipated rewards. Evidence is emerging that these regions and interconnecting pathways have sensitive exposure periods when they are most vulnerable.

CONCLUSIONS

Early deprivation and later abuse may have opposite effects on amygdala volume. Structural and functional abnormalities initially attributed to psychiatric illness may be a more direct consequence of abuse. Childhood maltreatment exerts a prepotent influence on brain development and has been an unrecognized confound in almost all psychiatric neuroimaging studies. These brain changes may be best understood as adaptive responses to facilitate survival and reproduction in the face of adversity. Their relationship to psychopathology is complex as they are discernible in both susceptible and resilient individuals with maltreatment histories. Mechanisms fostering resilience will need to be a primary focus of future studies.

Executive Function in Previously Institutionalized Children

In studies of children adopted from institutions, being raised in an institution has been associated consistently with an increased risk of persistent cognitive, academic, and social-emotional problems. These findings raise questions about the neurocognitive mechanisms that contribute to these negative outcomes. Theory and models based on studies of animals indicate that development of the prefrontal cortex (PFC) and executive function (EF) may be particularly susceptible to environmental influences during early childhood. In this article, we review recent studies of postinstitutionalized children that examined EF components such as inhibitory control, working memory, shifting, and planning. We then describe emerging research on the structure and function of the PFC. Converging evidence suggests both EF difficulties and alterations in development of the PFC following early institutionalization. We conclude by discussing possible explanations for these findings and implications for prevention and intervention, and by offering suggestions for ongoing research.

Brain-derived neurotrophic factor promoter methylation and cortical thickness in recurrent major depressive disorder

Recent studies have reported that methylation of the brain-derived neurotrophic factor (BDNF) gene promoter is associated with major depressive disorder (MDD). This study aimed to investigate the association between cortical thickness and methylation of BDNF promoters as well as serum BDNF levels in MDD. The participants consisted of 65 patients with recurrent MDD and 65 age- and gender-matched healthy controls. Methylation of BDNF promoters and cortical thickness were compared between the groups. The right medial orbitofrontal, right lingual, right lateral occipital, left lateral orbitofrontal, left pars triangularis, and left lingual cortices were thinner in patients with MDD than in healthy controls. Among the MDD group, right pericalcarine, right medical orbitofrontal, right rostral middle frontal, right postcentral, right inferior temporal, right cuneus, right precuneus, left frontal pole, left superior frontal, left superior temporal, left rostral middle frontal and left lingual cortices had inverse correlations with methylation of BDNF promoters. Higher levels of BDNF promoter methylation may be closely associated with the reduced cortical thickness among patients with MDD. Serum BDNF levels were significantly lower in MDD, and showed an inverse relationship with BDNF methylation only in healthy controls. Particularly the prefrontal and occipital cortices seem to indicate key regions in which BDNF methylation has a significant effect on structure.

Future Directions in Childhood Adversity and Youth Psychopathology

Despite long-standing interest in the influence of adverse early experiences on mental health, systematic scientific inquiry into childhood adversity and developmental outcomes has emerged only recently. Existing research has amply demonstrated that exposure to childhood adversity is associated with elevated risk for multiple forms of youth psychopathology. In contrast, knowledge of developmental mechanisms linking childhood adversity to the onset of psychopathology-and whether those mechanisms are general or specific to particular kinds of adversity-remains cursory. Greater understanding of these pathways and identification of protective factors that buffer children from developmental disruptions following exposure to adversity is essential to guide the development of interventions to prevent the onset of psychopathology following adverse childhood experiences. This article provides recommendations for future research in this area. In particular, use of a consistent definition of childhood adversity, integration of studies of typical development with those focused on childhood adversity, and identification of distinct dimensions of environmental experience that differentially influence development are required to uncover mechanisms that explain how childhood adversity is associated with numerous psychopathology outcomes (i.e., multifinality) and identify moderators that shape divergent trajectories following adverse childhood experiences. A transdiagnostic model that highlights disruptions in emotional processing and poor executive functioning as key mechanisms linking childhood adversity with multiple forms of psychopathology is presented as a starting point in this endeavour. Distinguishing between general and specific mechanisms linking childhood adversity with psychopathology is needed to generate empirically informed interventions to prevent the long-term consequences of adverse early environments on children's development.

Disruptions of working memory and inhibition mediate the association between exposure to institutionalization and symptoms of attention deficit hyperactivity disorder

BACKGROUND

Young children raised in institutions are exposed to extreme psychosocial deprivation that is associated with elevated risk for psychopathology and other adverse developmental outcomes. The prevalence of attention deficit hyperactivity disorder (ADHD) is particularly high in previously institutionalized children, yet the mechanisms underlying this association are poorly understood. We investigated whether deficits in executive functioning (EF) explain the link between institutionalization and ADHD.

METHOD

A sample of 136 children (aged 6-30 months) was recruited from institutions in Bucharest, Romania, and 72 never institutionalized community children matched for age and gender were recruited through general practitioners' offices. At 8 years of age, children's performance on a number of EF components (working memory, response inhibition and planning) was evaluated. Teachers completed the Health and Behavior Questionnaire, which assesses two core features of ADHD, inattention and impulsivity.

RESULTS

Children with history of institutionalization had higher inattention and impulsivity than community controls, and exhibited worse performance on working memory, response inhibition and planning tasks. Lower performances on working memory and response inhibition, but not planning, partially mediated the association between early institutionalization and inattention and impulsivity symptom scales at age 8 years.

CONCLUSIONS

Institutionalization was associated with decreased EF performance and increased ADHD symptoms. Deficits in working memory and response inhibition were specific mechanisms leading to ADHD in previously institutionalized children. These findings suggest that interventions that foster the development of EF might reduce risk for psychiatric problems in children exposed to early deprivation.

Early Adverse Experiences and the Developing Brain

Children exposed to various forms of adversity early in life are at increased risk for a broad range of developmental difficulties, affecting both cognitive and emotional adjustment. We review a growing body of evidence suggesting that exposure to adverse circumstances affects the developing brain in ways that increase risk for a myriad of problems. We focus on two forms of adversity, one in which children are exposed to childhood maltreatment in family environments, and another in which children are exposed to extreme psychosocial deprivation in contexts of institutional rearing. We discuss ways in which each of these experiences represent violations of species-expected caregiving conditions, thereby imposing challenges to the developing brain. We also review emerging data pointing to the effectiveness of early intervention in remediating neurodevelopmental consequences associated with maltreatment or institutional rearing. We conclude by discussing implications of this work for public health efforts and highlight important directions for the field.

Early Psychosocial Neglect Adversely Impacts Developmental Trajectories of Brain Oscillations and Their Interactions

Rhythmicity is a fundamental property of neural activity at multiple spatiotemporal scales, and associated oscillations represent a critical mechanism for communication and transmission of information across brain regions. During development, these oscillations evolve dynamically as a function of neural maturation and may be modulated by early experiences, positive and/or negative. This study investigated the impact of psychosocial deprivation associated with institutional rearing in early life and the effects of subsequent foster care intervention on developmental trajectories of neural oscillations and their cross-frequency correlations. Longitudinally acquired nontask EEGs from three cohorts of children from the Bucharest Early Intervention Project were analyzed. These included abandoned children initially reared in institutions and subsequently randomized to be placed in foster care or receive care as usual (prolonged institutional rearing) and a group of never-institutionalized children. Oscillation trajectories were estimated from 42 to 96 months, that is, 1-3 years after all children in the intervention arm of the study had been placed in foster care. Significant differences between groups were estimated for the amplitude trajectories of cognitive-related gamma, beta, alpha, and theta oscillations. Similar differences were identified as a function of time spent in institutions, suggesting that increased time spent in psychosocial neglect may have profound and widespread effects on brain activity. Significant group differences in cross-frequency coupling were estimated longitudinally between gamma and lower frequencies as well as alpha and lower frequencies. Lower cross-gamma coupling was estimated at 96 months in the group of children that remained in institutions at that age compared to the other two groups, suggesting potentially impaired communication between local and long-distance brain networks in these children. In contrast, higher cross-alpha coupling was estimated in this group compared to the other two groups at 96 months, suggesting impaired suppression of alpha-theta and alpha-delta activity, which has been associated with neuropsychiatric disorders. Age at foster care placement had a significant positive modulatory effect on alpha and beta trajectories and their mutual coupling, although by 96 months these trajectories remained distinct from those of never-institutionalized children. Overall, these findings suggest that early psychosocial neglect may profoundly impact neural maturation, particularly the evolution of neural oscillations and their interactions across a broad frequency range. These differences may result in widespread deficits across multiple cognitive domains.

Early deprivation and autonomic nervous system functioning in post-institutionalized children

The relations between early deprivation and the development of the neuroendocrine and central components of the mammalian stress response have been examined frequently. However, little is known about the impact of early deprivation on the developmental trajectories of autonomic function. Children adopted between 15-36 months from institutional care were examined during their first 16 months post-adoption (N = 60). Comparison groups included same-aged peers reared in their birth families (N = 50) and children adopted internationally from overseas foster care (N = 46). The present study examined trajectories of baseline autonomic nervous system function longitudinally following entry into adopted families. Post-institutionalized children had higher sympathetic tone, measured by pre-ejection period (PEP). Individual differences in PEP soon after adoption served as a mediator between early deprivation and parent-reported behavioral problems 2 years post-adoption. There were no group differences in parasympathetic function, indexed by respiratory sinus arrhythmia. All three groups showed similar trajectories of ANS function across the 16 month period.

Dorsal Anterior Cingulate Thickness Is Related to Alexithymia in Childhood Trauma-Related PTSD

Alexithymia, or “no words for feelings”, is highly prevalent in samples with childhood maltreatment and posttraumatic stress disorder (PTSD). The dorsal anterior cingulate cortex (dACC) has been identified as a key region involved in alexithymia, early life trauma, and PTSD. Functional alterations in the dACC also have been associated with alexithymia in PTSD. This study examined whether dACC morphology is a neural correlate of alexithymia in child maltreatment-related PTSD. Sixteen adults with PTSD and a history of childhood sexual abuse, physical abuse, or exposure to domestic violence, and 24 healthy controls (HC) completed the Toronto Alexithymia Scale 20 (TAS–20) and underwent magnetic resonance imaging. Cortical thickness of the dACC was measured using FreeSurfer, and values were correlated with TAS–20 scores, controlling for sex and age, in both groups. Average TAS–20 score was significantly higher in the PTSD than the HC group. TAS–20 scores were significantly positively associated with dACC thickness only in the PTSD group. This association was strongest in the left hemisphere and for TAS–20 subscales that assess difficulty identifying and describing feelings. We found that increasing dACC gray matter thickness is a neural correlate of greater alexithymia in the context of PTSD with childhood maltreatment. While findings are correlational, they motivate further inquiry into the relationships between childhood adversity, emotional awareness and expression, and dACC morphologic development in trauma-related psychopathology.

Recent advances in understanding the neurobiology of childhood socioeconomic disadvantage

PURPOSE OF REVIEW

To provide an update of recent research regarding neural mechanisms of socioeconomic disadvantage.

RECENT FINDINGS

The studies reviewed provide convincing evidence of the detrimental effects of early adversities on brain structure and function. The effects of socioeconomic disadvantage and related environmental risks, such as childhood adversity and smoking during pregnancy, while affecting distributed networks of brain regions, have decreased prefrontal activity and volume as a common feature.

SUMMARY

Recent work suggests that socioeconomic disadvantage and related risk factors may account for a significant proportion of variance in measures of brain structure and function, which may mediate the increased risk of psychopathology. Impaired prefrontal control may be a convergent mechanism underlying early exposure to socioeconomic risk factors in humans. Environmental imaging, that is, the impact which environmental adversity may have on brain structure and function, has only recently moved into the focus of interest. This is surprising because the link to psychopathology has long since been acknowledged and socioeconomic risk factors are modifiable, meaning that understanding their mechanism may point toward prevention and early intervention mechanisms. In future work, the interplay between different environmental risk factors, their potential epigenetic mechanisms, and their interaction with genetic risk should be studied.

The association between youth violence exposure and attention-deficit/hyperactivity disorder (ADHD) symptoms in a sample of fifth-graders

The purpose of the current study was to examine the association between violence exposures (no exposure, witness or victim only, and both witness and victim) and attention-deficit/hyperactivity disorder (ADHD) symptoms, as well as the potential moderating role of gender. Data from 4,745 5th graders and their primary caregivers were drawn from the Healthy Passages study of adolescent health. Parent respondents completed the DISC Predictive Scales for ADHD, and youth provided information about exposure to violence. Results indicated that youth who reported both witnessing and victimization had more parent-reported ADHD symptoms and were more likely to meet predictive criteria for ADHD. Among those with both exposures, girls exhibited a steeper increase in ADHD symptoms and higher probability of meeting predictive criteria than did boys. Findings indicate that being both victim-of and witness-to violence is significantly associated with ADHD symptoms particularly among girls.

The relationship between early adversities and attention-deficit/hyperactivity disorder

This study examined whether retrospectively reported childhood physical abuse, childhood sexual abuse and/or exposure to parental domestic violence were associated with self-report of a health-professional diagnosis of attention-deficit/hyperactivity disorder (ADHD) among adults. We analyzed nationally representative data from the 2012 Canadian Community Health Survey-Mental Health using gender-specific bivariate and logistic regression analyses (n=10,496 men; n=12,877 women). For both men and women, childhood physical abuse was associated with significantly higher odds of reporting ADHD (men odds ratio [OR]=1.66, p<.001; women OR=1.95, p<.001). For both genders, childhood sexual abuse was also significantly related to higher odds of ADHD (men OR=2.57, p<.001; women OR=2.55, p<.001); however, exposure to parental domestic violence was only associated with elevated odds of ADHD among women (men OR=0.89, p=.60; women OR=1.54, p=.03). The results demonstrate a link between childhood physical and sexual abuse and ADHD for both men and women. Future prospective studies are required to further understand this interesting relationship.

Childhood adversity and neural development: deprivation and threat as distinct dimensions of early experience

A growing body of research has examined the impact of childhood adversity on neural structure and function. Advances in our understanding of the neurodevelopmental consequences of adverse early environments require the identification of dimensions of environmental experience that influence neural development differently and mechanisms other than the frequently-invoked stress pathways. We propose a novel conceptual framework that differentiates between deprivation (absence of expected environmental inputs and complexity) and threat (presence of experiences that represent a threat to one's physical integrity) and make predictions grounded in basic neuroscience principles about their distinct effects on neural development. We review animal research on fear learning and sensory deprivation as well as human research on childhood adversity and neural development to support these predictions. We argue that these previously undifferentiated dimensions of experience exert strong and distinct influences on neural development that cannot be fully explained by prevailing models focusing only on stress pathways. Our aim is not to exhaustively review existing evidence on childhood adversity and neural development, but to provide a novel framework to guide future research.

Psychological Consequences of Early Global Deprivation

The English & Romanian Adoptees (ERA) study follows children who spent their first years of life in extremely depriving Romanian institutions before they were adopted by families in the UK. The ERA study constitutes a “natural experiment” that allows the examination of the effects of radical environmental change from a profoundly depriving institutional environment to an adoptive family home. The cohort has been assessed at ages 4, 6, 11, and 15 years, and has provided seminal insights into the effects of early global deprivation. The current paper focuses on the long-term psychological sequelae associated with deprivation experiences. These deprivation-specific problems (DSPs) constitute a striking pattern of behavioral impairments, in its core characterized by deficits in social cognition and behavior, as well as quasi-autistic features, often accompanied by cognitive impairment and symptoms of attention-deficit/hyperactivity disorder (ADHD). Possible moderating influences, including variations in family environment, pre-adoption characteristics, and genetic variation, will be discussed to answer the question why some individuals have prospered while others have struggled. Apart from findings on the moderating effect of variation in genes associated with serotonergic and dopaminergic signaling involving specific phenotypes, heterogeneity in outcome is largely unexplained. The review concludes with an outlook on currently ongoing and future research of the ERA study cohort, which involves the investigation of neurobiological and epigenetic mechanisms as possible mediators of the long-term effects of institutional deprivation.

Prenatal Alcohol Exposure is Associated with Regionally Thinner Cortex During the Preadolescent Period

Children with fetal alcohol spectrum disorders (FASD) may exhibit craniofacial dysmorphology, neurobehavioral deficits, and reduced brain volume. Studies of cortical thickness in FASD have yielded contradictory findings, with 3 reporting thicker cerebral cortex in frontal and temporal brain regions and 2 showing thinner cortex across multiple regions. All 5 studies included subjects spanning a broad age range, and none have examined continuous measures of prenatal alcohol exposure. We investigated the relation of extent of in utero alcohol exposure to cortical thickness in 78 preadolescent children with FASD and controls within a narrow age range. A whole-brain analysis using FreeSurfer revealed no significant clusters where cortical thickness differed by FASD diagnostic group. However, alcohol dose/occasion during pregnancy was inversely related to cortical thickness in 3 regions-right cuneus/pericalcarine/superior parietal lobe, fusiform/lingual gyrus, and supramarginal/postcentral gyrus. The effect of prenatal alcohol exposure on IQ was mediated by cortical thickness in the right occipitotemporal region. It is noteworthy that a continuous measure of maternal alcohol consumption during pregnancy was more sensitive than FASD diagnosis and that the effect on cortical thickness was most evident in relation to a measure of maternal binge drinking.

Psychostimulants and atomoxetine alter the electrophysiological activity of prefrontal cortex neurons, interaction with catecholamine and glutamate NMDA receptors

RATIONALE

Attention-deficit hyperactivity disorder (ADHD) is the most frequently diagnosed neuropsychiatric disorder in childhood. Currently available ADHD drugs include the psychostimulants methylphenidate (MPH) and D-amphetamine (D-AMP), acting on norepinephrine and dopamine transporters/release, and atomoxetine (ATX), a selective norepinephrine uptake inhibitor. Recent evidence suggests an involvement of glutamate neurotransmission in the pathology and treatment of ADHD, via mechanisms to be clarified.

OBJECTIVE

We have investigated how ADHD drugs could modulate, through interaction with catecholamine receptors, basal and glutamate-induced excitability of pyramidal neurons in the prefrontal cortex (PFC), a region which plays a major role in control of attention and impulsivity.

METHODS

We have used the technique of extracellular single-unit recording in anaesthetised rats coupled with microiontophoresis.

RESULTS

Both MPH (1-3 mg/kg) and D-AMP (1-9 mg/kg) increased the firing activity of PFC neurons in a dopamine D1 receptor-dependent manner. ATX administration (1-6 mg/kg) also increased the firing of neurons, but this effect is not significantly reversed by D1 (SCH 23390) or alpha1 (prazosin) receptor antagonists but potentiated by alpha2 antagonist (yohimbine). All drugs induced a clear potentiation of the excitatory response of PFC neurons to the microiontophoretic application of the glutamate agonist N-methyl-D-aspartate (NMDA), but not to the glutamate agonist α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA). The potentiating effect of D-AMP on NMDA-induced activation of PFC neurons was partially reversed or prevented by dopamine D1 receptor blockade.

CONCLUSION

Our data shows that increase in excitability of PFC neurons in basal conditions and via NMDA receptor activation may be involved in the therapeutic response to ADHD drugs.

ADHD symptomatology is best conceptualized as a spectrum: a dimensional versus unitary approach to diagnosis

The aim of this paper is to build a case for the utility of conceptualizing ADHD, not as a unitary disorder that contains several subtypes, but rather as a marker of impairment in attention and/or impulsivity that can be used to identify one of several disorders belonging to a spectrum. The literature will be reviewed to provide an overview of what is known about ADHD in terms of heterogeneity in symptomatology, neuropsychology, neurobiology, as well as comorbidity with other diseases and treatment options. The data from these areas of research will be critically analyzed to support the construct of a spectrum of disorders that can capture the great variability that exists between individuals with ADHD and can discriminate between separate disorders that manifest similar symptoms. The symptoms associated with ADHD can be viewed as dimensional markers that point to a spectrum of related disorders that have as part of their characteristics impairments of attention and impulsivity. The spectrum can accommodate symmetrically and asymmetrically comorbid psychiatric disorders associated with ADHD as well as the wide heterogeneity known to be a part of the ADHD disorder. Individuals presenting with impairments associated with ADHD should be treated as having a positive marker for a spectrum disorder that has as part of its characteristics impairments of attention and/or impulsivity. The identification of impairment in attention and/or impulsivity should be a starting point for further testing rather than being an endpoint of diagnosis that results in pharmacological treatment that may or may not be the optimal therapy. Rather than continuing to attribute a large amount of heterogeneity in symptom presentation as well as a high degree of symmetric and asymmetric comorbidity to a single disorder, clinical evaluation should turn to the diagnosis of the type of attentional deficit and/or impulsivity an individual has in order to colocate the individual's disorder on a spectrum that captures the heterogeneity in symptomatology, the symmetrical and asymmetrical comorbidity, as well as subthreshold presentation and other variants often worked into the disorder of ADHD. The spectrum model can accommodate not only the psychophysiological profiles of patients, but is also consistent with what is known about the functional heterogeneity of the prefrontal cortex as well as the construct that cognitive processes are supported by overlapping and collaborative networks.

Institutional care and iron deficiency increase ADHD symptomology and lower IQ 2.5-5 years post-adoption

Increased ADHD symptomology and lower IQ have been reported in internationally adopted (IA) children compared to non-adopted peers (Hostinar, Stellern, Schaefer, Carlson & Gunnar, 2012; Kreppner, O'Connor & Rutter, 2001). However, it is unclear whether these outcomes are due to institutional deprivation specifically or to co-occurring micronutrient deficiencies that disrupt brain development (Fuglestad, Rao & Georgieff, 2008b). In this study, IA children were compared to children raised in their biological families to examine differences in ADHD symptomology and IQ 2.5-5 years post-adoption and to assess the contributions of iron deficiency (ID) and duration of deprivation to these cognitive outcomes. ADHD symptoms (parent- and experimenter-reported) and IQ were evaluated in 88 IA (M = 62.1 months, SD = 2.4) and 35 non-adopted children (M = 61.4 months, SD = 1.6). IA children were assessed 29-64 months post-adoption (M = 41.9 months, SD = 10.2). ID was assessed during the initial post-adoption medical visit in 69 children, and children were classified into four groups by iron status, ranging from normal to ID anemia (most severe). IA children had greater ADHD symptomology, p < .01, and lower IQ, p = .001, than non-adopted children. Within the IA group, children with more severe ID at adoption had greater ADHD symptomology, r(69) = 0.40, p = .001, and lower IQ, r(68) = -0.28, p < .05. Duration of institutional care was positively correlated with ADHD symptoms, r(86) = .28, p < .01, but not IQ, r(85) = -.08, p = .52. Longitudinal results indicate improvement in IQ from 12 months post-adoption to age 5 for children with greater ID severity at adoption and longer duration of institutional care but no improvement in ADHD symptoms. These results signify continuing effects of early deprivation and ID on ADHD symptoms and IQ years after adoption. A video abstract of this article can be viewed at http://www.youtube.com/watch?v=vUFDAS3DD1c.

Effect of early institutionalization and foster care on long-term white matter development: a randomized clinical trial

IMPORTANCE

Severe neglect in early life is associated with compromises in brain development and associated behavioral functioning. Although early intervention has been shown to support more normative trajectories of brain development, specific improvements in the white matter pathways that underlie emotional and cognitive development are unknown.

OBJECTIVE

To examine associations among neglect in early life, early intervention, and the microstructural integrity of white matter pathways in middle childhood.

DESIGN, SETTING, AND PARTICIPANTS

The Bucharest Early Intervention Project is a randomized clinical trial of high-quality foster care as an intervention for institutionally reared children in Bucharest, Romania, from 2000 through the present. During infancy, children were randomly selected to remain in an institution or to be placed in foster care. Those who remained in institutions experienced neglect, including social, emotional, linguistic, and cognitive impoverishment. Developmental trajectories of these children were compared with a group of sociodemographically matched children reared in biological families at baseline and several points throughout development. At approximately 8 years of age, 69 of the original 136 children underwent structural magnetic resonance imaging scans.

MAIN OUTCOMES AND MEASURES

Four estimates of white matter integrity (fractional anisotropy [FA] and mean [MD], radial [RD], and axial [AD] diffusivity) for 48 white matter tracts throughout the brain were obtained through diffusion tensor imaging.

RESULTS

Significant associations emerged between neglect in early life and microstructural integrity of the body of the corpus callosum (FA, β = 0.01 [P = .01]; RD, β = -0.02 [P = .005]; MD, β = -0.01 [P = .02]) and tracts involved in limbic circuitry (fornix crus [AD, β = 0.02 (P = .046)] and cingulum [RD, β = -0.01 (P = .02); MD, β = -0.01 (P = .049)]), frontostriatal circuitry (anterior [AD, β = -0.01 (P = .02)] and superior [AD, β = -0.02 (P = .02); MD, β = -0.01 (P = .03)] corona radiata and external capsule [right FA, β = 0.01 (P = .03); left FA, β = 0.01 (P = .03); RD, β = -0.01 (P = .01); MD, β = -0.01 (P = .03)]), and sensory processing (medial lemniscus [AD, β = -0.02 (P = .045); MD, β = -0.01 (P = .04)] and retrolenticular internal capsule [FA, β = -0.01 (P = .002); RD, β = 0.01 (P = .003); MD, β = 0.01 (P = .04)]). Follow-up analyses revealed that early intervention promoted more normative white matter development among previously neglected children who entered foster care.

CONCLUSIONS AND RELEVANCE

Results suggest that removal from conditions of neglect in early life and entry into a high-quality family environment can support more normative trajectories of white matter growth. Our findings have implications for public health and policy efforts designed to promote normative brain development among vulnerable children.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00747396.

Behavioral problems after early life stress: contributions of the hippocampus and amygdala

BACKGROUND

Early life stress (ELS) can compromise development, with higher amounts of adversity linked to behavioral problems. To understand this linkage, a growing body of research has examined two brain regions involved with socioemotional functioning-amygdala and hippocampus. Yet empirical studies have reported increases, decreases, and no differences within human and nonhuman animal samples exposed to different forms of ELS. This divergence in findings may stem from methodological factors, nonlinear effects of ELS, or both.

METHODS

We completed rigorous hand-tracing of the amygdala and hippocampus in three samples of children who experienced different forms of ELS (i.e., physical abuse, early neglect, or low socioeconomic status). Interviews were also conducted with children and their parents or guardians to collect data about cumulative life stress. The same data were also collected in a fourth sample of comparison children who had not experienced any of these forms of ELS.

RESULTS

Smaller amygdala volumes were found for children exposed to these different forms of ELS. Smaller hippocampal volumes were also noted for children who were physically abused or from low socioeconomic status households. Smaller amygdala and hippocampal volumes were also associated with greater cumulative stress exposure and behavioral problems. Hippocampal volumes partially mediated the relationship between ELS and greater behavioral problems.

CONCLUSIONS

This study suggests ELS may shape the development of brain areas involved with emotion processing and regulation in similar ways. Differences in the amygdala and hippocampus may be a shared diathesis for later negative outcomes related to ELS.

Deviations from the expectable environment in early childhood and emerging psychopathology

Current frameworks for understanding the link between early adverse childhood experiences and later negative life outcomes, including psychopathology, focus on the mediating negative impact on brain and biological systems in the developing child resulting broadly from stress and trauma. Although this approach is useful, we argue that the framework could be functionally extended by distinguishing the effects of two different types of abnormal input, both deviations from the expectable environment in early childhood. Specifically, we review the consequences of inadequate input (eg, neglect/deprivation) and harmful input (eg, abuse/trauma) on brain and biological development. We then review evidence on the differential links between each type of abnormal input to four selected domains of psychopathology (indiscriminate social behavior, posttraumatic stress disorder, attention-deficit/hyperactivity disorder, and conduct problems), and consider potential mechanisms for inadequate and harmful input to lead to these outcomes. We conclude that the careful consideration of the type of deviation from the expected environment, while acknowledging the practical difficulties in assessing this, is likely to lead to clearer understanding of the mechanism of risk for psychopathology, and that tailored approaches to prevention and intervention may be informed by considering the unique consequences of inadequate and harmful input when experienced in early childhood.

Beyond a means of exposure: a new view of the mother in toxicology research

Toxicological studies generally view pregnant animals as a conduit through which gestational exposure of offspring to chemicals can be achieved, allowing for the study of developmental toxicity.

Duration of early adversity and structural brain development in post-institutionalized adolescents

For children reared in institutions for orphaned or abandoned children, multiple aspects of the early environment deviate from species-typical experiences, which may lead to alterations in neurobehavioral development. Although the effects of early deprivation and early life stress have been studied extensively in animal models, less is known about implications for human brain development. This structural neuroimaging study examined the long-term neural correlates of early adverse rearing environments in a large sample of 12-14 year old children (N = 110) who were internationally adopted from institutional care as young children (median age at adoption = 12 months) relative to a same age, comparison group reared with their biological families in the United States. History of institutional rearing was associated with broad changes in cortical volume even after controlling for variability in head size. Results suggested that prefrontal cortex was especially susceptible to early adversity, with significant reductions in volume (driven primarily by differences in surface area rather than cortical thickness) in post-institutionalized youth. Hippocampal volumes showed an association with duration of institutional care, with later-adopted children showing the smallest volumes relative to non-adopted controls. Larger amygdala volumes were not detected in this sample of post-institutionalized children. These data suggest that this temporally discrete period of early deprivation is associated with persisting alterations in brain morphology even years after exposure. Furthermore, these alterations are not completely ameliorated by subsequent environmental enrichment by early adolescence.

Dimensions of early experience and neural development: deprivation and threat

Over the past decade, a growing area of research has focused on adverse childhood experiences (ACEs) and their impacts on neural and developmental outcomes. Work in the field to-date has generally conceptualized ACEs in terms of exposure to stress while overlooking the underlying dimensions of environmental experience that may distinctly impact neural development. Here, we propose a novel framework that differentiates between deprivation (absence of expected cognitive and social input) and threat (presence of a threat to one's physical integrity). We draw support for the neural basis of this distinction from studies on fear learning and sensory deprivation in animals to highlight potential mechanisms through which experiences of threat and deprivation could affect neural structure and function in humans.