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3 The Interaction of Biology and Environment
Pages 57-84

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From page 57...
... . These ­ remarkable developmental events contribute to the entire, elaborate ­ rraya of individual life attributes and trajectories, from personality, intelligence, and individual achievement to lifelong risks for disease, disorder, and criminality.
From page 58...
... proved a pivotal moment in the integration and dissemination of the insights gained from new knowledge of developmental processes. That report assembles and compellingly presents the evidence that early child development is critically dependent upon relationships with caring and teaching adults, that individual biology and social experiences are equally influential in determining developmental outcomes, and that infants are born able and ready to learn.
From page 59...
... Fourth, inquiry into the sources of special vulnerability and resilience with respect to early adversity has led to the discovery of substantial individual differences in children's susceptibilities to both negative and positive environmental exposures. This discovery has reinforced the unique character of each child's responses to the physical and social worlds, has offered perspectives on why some children thrive within environments of great adversity, and has illuminated seemingly contradictory findings about how social conditions affect health and development.
From page 60...
... Over the remaining weeks of gestation, primitive cells differentiate into specialized cells and brain regions with distinctive forms and functions. Precursor neural cells differentiate into neurons and glia cells; the former appear at 5 to 25 weeks of gestation and play key roles in the execution of brain functions, while the latter appear later in prenatal development and have key structural and functional supportive functions in the brain and nervous system.
From page 61...
... Many of the psychotropic medications currently used for disorders such as depression and anxiety act upon the molecular mechanisms involved in synaptic communication. The rate of formation of both new neurons and new synapses during prenatal brain development is staggering.
From page 62...
... 62 Developmental Phase Early Early Emerging Prenatal Birth Infancy Childhood Childhood Adolescence Adolescence Adulthood Gestation (weeks) 4 8 12 16 20 24 28 32 Neurulation Neuronal Proliferation Neuronal Differentiation Neuronal Migration Synapse Formation Programmed Cell Death Synaptic Pruning Myelination FIGURE 3-2  Developmental phases of neural development.
From page 63...
... For example, growing evidence points to the specialized dominance of the right side of the brain in processing social and emotional information, including nonverbal information, which are the foundation of important functions such as interpreting social stimuli, understanding the emotions and intentions of others, and engaging in social interactions, including the important development of attachment in very young children (De Pisapia et al., 2014; Decety and Lamm, 2007; Hecht, 2014; Schore, 2014; SemrudClikeman et al., 2011)
From page 64...
... Prenatally, such disturbances can include, for example, deficiencies in folate in the maternal diet, which can result in severely disordered formation of the brain and spine, and infection with such organisms as toxoplasmosis or cytomegalovirus, which can produce severe forms of psychopathology such as schizophrenia or autism. In early childhood, one perturbation that occurs with great prevalence in human populations is the developing brain's exposure, directly or indirectly through the parents' experiences, to substantial psychosocial adversity and stress, such as abuse or neglect, the death of a parent, or exposure to violence in the home or neighborhood.
From page 65...
... The second, GxE, describes genetic or environmental effects that are conditional upon each other -- for example, the effects of genetic variation that become apparent only in the presence of specific environmental conditions, or the effects of social contexts that are more or less potent depending on the under­ lying genotype of the individual who experiences them. Third, epigenetic processes that stem from environmental exposures modify chromatin -- the structural packaging of the genome -- through the chemical "tagging" of DNA or the histone proteins around which it is wound.
From page 66...
... . How GxE interaction exerts effects on developmental and behavioral outcomes has been explained in part by studies showing how variations in DNA sequence are linked to connectivity in specific brain regions (Thompson et al., 2010)
From page 67...
... , allows or disallows access to gene coding regions by RNA polymerase, the enzyme that decodes DNA sequences. Which chromatin conformation exists at a given time depends on epigenetic processes of chemical modification or "marking" that modifies either the DNA itself or the histone proteins around which the DNA is wrapped.
From page 68...
... Thus, a single set of molecular processes serve both stability and change -- an "epigenetic paradox" of the same molecular mechanisms providing for contrasting cellular needs. Paradoxical though they may be, the uses and functions of epigenetic processes play critically important roles in the successful emergence of social, educational, and biological capacities.
From page 69...
... Laboratory investigation of this GxE interaction revealed that the effect is mediated through epigenetic changes in a cortisol response element in the gene. This observation shows how chromatin modification and epigenetic marks may be a molecular mechanism for GxE interactions.
From page 70...
... . The developing brain is also especially vulnerable to the effects of physical and social environmental exposures during early developmental periods.
From page 71...
... Chapter 4 places those biological consequences in the context of broader considerations and consequences having to do with chronic stress and adversity, focusing in particular on the stressors associated with economic adversity; social buffering of stress; and the relationships among stress, learning, and mental health. Importantly, children experience stress -- and the biological dysregulation that can occur -- not only as a result of the active stressors of chronic threat or danger but also because of the unavailability of nurturing, supportive care on which children rely, especially early in life.
From page 72...
... Over time, however, chronic stress and repeated exposures to adversity can alter the brain centers and neuroendocrine circuitry that underlie the regulation of stress responses and change the functioning of the HPA axis (Ulrich-Lai and Herman, 2009)
From page 73...
... There is growing evidence that the biological embedding of chronic stress begins prenatally because fetal development is affected by the hormonal, autonomic, and other physiologic correlates of maternal stress. Prenatal exposure to cortisol, for example, can have profound influences on the developing brain, as some portion of maternally secreted cortisol moves through the placenta and affects the fetus's neurodevelopment.
From page 74...
... In other words, in addition to other disadvantages they experience, one reason children in stressful circumstances fall behind academically is that the biological effects of stress impair their capacities for concentrated attention, memory, cognitive self-regulation, language, and focused thinking. One of the reasons these children experience social difficulties, such as peer conflict or poor compliance with teachers, is that the biological effects of stress enhance their emotional reactivity, heighten their threat vigilance, and undermine their emotion regulation and impulse control.
From page 75...
... They also found that heightened cortisol was associated with decreases in the expression of the glucocorticoid receptor gene in the infants. Changes in gene expression in the child helped account, in other words, for the enduring influence of prenatal maternal stress.
From page 76...
... Together, these findings indicate that while all children exhibit responsiveness to environmental influences, a subset of children show an exaggerated susceptibility to the character of their social environments -- heightened risk for morbidity and developmental deviation when reared in harsh, unsupportive conditions but higher levels of health and positive development if reared in environments characterized by nurturance and support. Such children almost certainly contribute substantially to the uneven distribution of ill health, learning difficulties, and troubled development found within childhood populations.
From page 77...
... 2012. Child development in the context of adversity: Experiential canalization of brain and behavior.
From page 78...
... An evolutionary developmental theory of the origins and functions of stress reactivity. Development and Psychopathology 17(2)
From page 79...
... Journal of Child Psychology and Psychiatry and Allied Disciplines 46(11)
From page 80...
... 2009. Socioeconomic status and the developing brain.
From page 81...
... 2009. Epigenetic regulation of the glucocorticoid receptor in human brain associates with childhood abuse.
From page 82...
... 2008. Prenatal exposure to maternal depression, neonatal methylation of human glucocorticoid receptor gene (NR3C1)
From page 83...
... 2004. Early environmental regulation of hippocampal glucocorticoid receptor gene expression: Characterization of intracellular mediators and potential genomic target sites.


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