Eamon McCrory

Research Review: The neurobiology and genetics of maltreatment and adversity

The neurobiological mechanisms by which childhood maltreatment heightens vulnerability to psychopathology remain poorly understood. It is likely that a complex interaction between environmental experiences (including poor caregiving) and an individuals genetic make-up influence neurobiological development across infancy and childhood, which in turn sets the stage for a childs psychological and emotional development. This review provides a concise synopsis of those studies investigating the neurobiological and genetic factors associated with childhood maltreatment and adversity. We first provide an overview of the neuroendocrine findings, drawing from animal and human studies. These studies indicate an association between early adversity and atypical development of the hypothalamic-pituitary-adrenal (HPA) axis stress response, which can predispose to psychiatric vulnerability in adulthood. We then review the neuroimaging findings of structural and functional brain differences in children and adults who have experienced childhood maltreatment. These studies offer evidence of several structural differences associated with early stress, most notably in the corpus callosum in children and the hippocampus in adults; functional studies have reported atypical activation of several brain regions, including decreased activity of the prefrontal cortex. Next we consider studies that suggest that the effect of environmental adversity may be conditional on an individuals genotype. We also briefly consider the possible role that epigenetic mechanisms might play in mediating the impact of early adversity. Finally we consider several ways in which the neurobiological and genetic research may be relevant to clinical practice and intervention.

Amygdala Response to Preattentive Masked Fear in Children With Conduct Problems: The Role of Callous-Unemotional Traits

OBJECTIVE In children with conduct problems, high levels of callous-unemotional traits are associated with amygdala hypoactivity to consciously perceived fear, while low levels of callous-unemotional traits may be associated with amygdala hyperactivity. Behavioral data suggest that fear processing deficits in children with high callous-unemotional traits may extend to stimuli presented below conscious awareness (preattentively). The authors investigated the neural basis of this effect. Amygdala involvement was predicted on the basis of its role in preattentive affective processing in healthy adults and its dysfunction in previous studies of conduct problems. METHOD Functional MRI was used to measure neural responses to fearful and calm faces presented preattentively (for 17 ms followed by backward masking) in boys with conduct problems and high callous-unemotional traits (N=15), conduct problems and low callous-unemotional traits (N=15), and typically developing comparison boys (N=16). Amygdala response to fearful and calm faces was predicted to differentiate groups, with the greatest response in boys with conduct problems and low callous-unemotional traits and the lowest in boys with conduct problems and high callous-unemotional traits. RESULTS In the right amygdala, a greater amygdala response was seen in boys with conduct problems and low callous-unemotional traits than in those with high callous-unemotional traits. The findings were not explained by symptom levels of conduct disorder, attention-deficit hyperactivity disorder, anxiety, or depression. CONCLUSIONS These data demonstrate differential amygdala activity to preattentively presented fear in children with conduct problems grouped by callous-unemotional traits, with high levels associated with lower amygdala reactivity. The studys findings complement increasing evidence suggesting that callous-unemotional traits are an important specifier in the classification of children with conduct problems.

The impact of childhood maltreatment: a review of neurobiological and genetic factors.

Childhood maltreatment represents a significant risk factor for psychopathology. Recent research has begun to examine both the functional and structural neurobiological correlates of adverse care-giving experiences, including maltreatment, and how these might impact on a child’s psychological and emotional development. The relationship between such experiences and risk for psychopathology has been shown to vary as a function of genetic factors. In this review we begin by providing a brief overview of neuroendocrine findings, which indicate an association between maltreatment and atypical development of the hypothalamic–pituitary–adrenal axis stress response, which may predispose to psychiatric vulnerability in adulthood. We then selectively review the magnetic resonance imaging (MRI) studies that have investigated possible structural and functional brain differences in children and adults who have experienced childhood maltreatment. Differences in the corpus callosum identified by structural MRI have now been reliably reported in children who have experienced abuse, while differences in the hippocampus have been reported in adults with childhood histories of maltreatment. In addition, there is preliminary evidence from functional MRI studies of adults who have experienced childhood maltreatment of amygdala hyperactivity and atypical activation of frontal regions. These functional differences can be partly understood in the context of the information biases observed in event-related potential and behavioral studies of physically abused children. Finally we consider research that has indicated that the effect of environmental adversity may be moderated by genotype, reviewing pertinent studies pointing to gene by environment interactions. We conclude by exploring the extent to which the growing evidence base in relation to neurobiological and genetic research may be relevant to clinical practice and intervention.

The link between child abuse and psychopathology: A review of neurobiological and genetic research

Childhood abuse is associated with later psychopathology, including conduct disorder, antisocial personality disorder, anxiety and depression as well as a heightened risk of health and social problems. However, the neurobiological mechanisms by which childhood adversity increases vulnerability to psychopathology remain poorly understood. There is likely to be a complex interaction between environmental experiences (such as abuse) and individual differences in risk versus protective genes, which influences the neurobiological circuitry underpinning psychological and emotional development. Neuroendocrine studies indicate an association between early adversity and atypical development of the hypothalamic-pituitary-adrenal (HPA) axis stress response, which may predispose to psychiatric vulnerability in adulthood. Brain imaging research in children and adults is providing evidence of several structural and functional brain differences associated with early adversity. Structural differences have been reported in the corpus callosum, cerebellum and prefrontal cortex. Functional differences have been reported in regions implicated in emotional and behavioural regulation, including the amygdala and anterior cingulate cortex. These differences at the neurobiological level may represent adaptations to early experiences of heightened stress that lead to an increased risk of psychopathology. We also consider the clinical implications of future neurobiological and genetic research.

Association of Callous Traits with Reduced Neural Response to Others’ Pain in Children with Conduct Problems

Summary Children with conduct problems (CP) persistently violate others’ rights and represent a considerable societal cost [1]. These children also display atypical empathic responses to others’ distress [2], which may partly account for their violent and antisocial behavior. Callous traits index lack of empathy in these children and confer risk for adult psychopathy [3]. Investigating neural responses to others’ pain is an ecologically valid method to probe empathic processing [4], but studies in children with CP have been inconclusive [5, 6]. Using functional magnetic resonance imaging (fMRI), we measured neural responses to pictures of others in pain (versus no pain) in a large sample of children with CP and matched controls. Relative to controls, children with CP showed reduced blood oxygen level-dependent responses to others’ pain in bilateral anterior insula (AI), anterior cingulate cortex (ACC), and inferior frontal gyrus, regions associated with empathy for pain in previous studies [7, 8]. In the CP group, callous traits were negatively associated with responses to others’ pain in AI and ACC. We conclude that children with CP have atypical neural responses to others’ pain. The negative association between callous traits and AI/ACC response could reflect an early neurobiological marker indexing risk for empathic deficits seen in adult psychopathy.

Genetic and neurocognitive contributions to the development of psychopathy.

An overview is provided of recent twin, molecular genetic, and magnetic resonance imaging studies that are helping to inform a model of developmental vulnerability to adult psychopathy. Although the current evidence base suggests that children with high levels of callous-unemotional traits are genetically and neurocognitively vulnerable to developing psychopathic and antisocial behaviors, existing research also clearly indicates that environmental influences play an important role. One potential implication is that interventions for children with antisocial behavior and callous-unemotional traits may need to be tailored to take into account their distinct pattern of neurocognitive vulnerability, as revealed by developmental neuroimaging studies. Specifically, interventions that pursue punishment-oriented or explicit empathy induction strategies may be less effective with this group of antisocial children. By contrast, preliminary evidence suggests that enhancing positive parenting and parental involvement, as well as applying consistent rewards may represent more promising intervention approaches.

Cortical thickness, surface area, and gyrification abnormalities in children exposed to maltreatment: neural markers of vulnerability?

BACKGROUND Childhood maltreatment has been shown to significantly elevate the risk of psychiatric disorder. Previous neuroimaging studies of children exposed to maltreatment have reported atypical neural structure in several regions, including the prefrontal cortex and temporal lobes. These studies have exclusively investigated volumetric differences rather than focusing on genetically and developmentally distinct indices of brain structure. METHODS Here we used surface-based methods to examine cortical thickness, surface area, and local gyrification in a community sample of children with documented experiences of abuse (n = 22) and a group of carefully matched nonmaltreated peers (n = 21). RESULTS Reduced cortical thickness in the maltreated compared with the nonmaltreated group was observed in an extended cluster that incorporated the anterior cingulate, superior frontal gyrus, and orbitofrontal cortex. In addition, reduced cortical surface area was observed within the parcellated regions of the left middle temporal area and lingual gyrus. Local gyrification deficits within the maltreated group were located within two clusters, the lingual gyrus and the insula extending into pars opercularis. CONCLUSIONS This is the first time structural abnormalities in the anterior cingulate and lingual gyrus have been detected in children exposed to maltreatment. Surface-based methods seem to capture subtle, previously undetected, morphological abnormalities associated with maltreatment. We suggest that these approaches detect developmental precursors of brain volume differences seen in adults with histories of abuse. Because the reported regions are implicated in several clinical disorders, they might constitute biological markers of vulnerability, linking exposure to early adversity and psychiatric risk.

Effects of stressful life events on human brain structure: a longitudinal voxel-based morphometry study.

Although stressful life events (SLEs) have been associated with an increased risk of illness and mental disorder, their impact on brain anatomy remains poorly understood. Using a longitudinal design, we tested the hypothesis that SLEs are significantly associated with changes in gray matter volume (GMV) in brain regions previously implicated in post-traumatic stress disorder (PTSD) in a group of clinically healthy adults. Magnetic resonance imaging was used to acquire an anatomical scan from 26 subjects (13 males and 13 females; mean age ± SD: 25.2 ± 4.3 years), with no psychiatric diagnosis, at two time points with a 3-month interval. Voxel-based morphometry was used to examine an association between SLEs and gray matter changes during this period. The number of SLEs was associated with a decrease in GMV in the anterior cingulate, hippocampus, and parahippocampal gyrus (p < 0.001). In contrast, there were no areas where the number of SLEs was associated with an increase in GMV. These results provide evidence that, in adults with no formal psychiatric diagnosis, SLEs are associated with GMV decreases in a subset of regions implicated in PTSD, and that these alterations can be observed within a period as short as 3 months.

Abnormal Functional Activation During a Simple Word Repetition Task: A PET Study of Adult Dyslexics

Eight dyslexic subjects, impaired on a range of tasks requiring phonological processing, were matched for age and general ability with six control subjects. Participants were scanned using positron emission tomography (PET) during three conditions: repeating real words, repeating pseudowords, and rest. In both groups, speech repetition relative to rest elicited widespread bilateral activation in areas associated with auditory processing of speech; there were no significant differences between words and pseudowords. However, irrespective of word type, the dyslexic group showed less activation than the control group in the right superior temporal and right post-central gyri and also in the left cerebellum. Notably, the right anterior superior temporal cortex (Brodmanns area 22 [BA 22]) was less activated in each of the eight dyslexic subjects, compared to each of the six control subjects. This deficit appears to be specific to auditory repetition as it was not detected in a previous study of reading which used the same sets of stimuli (Brunswick, N., McCrory, E., Price, C., Frith, C.D., & Frith, U. [1999]. Explicit and implicit processing of words and pseudowords by adult developmental dyslexics: A search for Wernickes Wortschatz? Brain, 122, 1901-1917). This implies that the observed neural manifestation of developmental dyslexia is task-specific (i.e., functional rather than structural). Other studies of normal subjects indicate that attending to the phonetic structure of speech leads to a decrease in right-hemisphere processing. Lower right hemisphere activation in the dyslexic group may therefore indicate less processing of non-phonetic aspects of speech, allowing greater salience to be accorded to phonological aspects of attended speech.

The theory of latent vulnerability: Reconceptualizing the link between childhood maltreatment and psychiatric disorder.

Maltreatment in childhood is associated with a significantly increased likelihood of psychiatric disorder that endures across the life span. If disorders emerge they tend to be more severe and less responsive to treatment. We introduce the concept of latent vulnerability as a way of conceptualizing the nature of this psychiatric risk. We argue that vulnerability to mental health problems can be understood as changes in a suite of neurocognitive systems that reflect adaptation or altered calibration to early neglectful or maltreating environments. Altered threat processing is presented as one exemplar candidate system. Heightened neurocognitive vigilance to threat is argued to reflect a calibration to an early at-risk environment that becomes maladaptive (and instantiates vulnerability) in the longer term. Other neurocognitive domains, including reward and memory processing, represent equally promising candidates for indexing latent vulnerability and warrant future enquiry. We suggest that the operationalization of latent vulnerability has the potential to guide a preventative psychiatry approach. Intervention currently occurs at two stages when maltreatment is confirmed: first, by addressing issues of risk; and second, by providing clinical intervention if a child meets criteria for psychiatric disorder. We argue that indexing latent vulnerability represents a third intervention opportunity, with the potential to target an indicated prevention approach for the most vulnerable children, offsetting risk trajectories before psychiatric disorders emerge.