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3 How Environment "Gets Under the Skin": The Continuous Interplay Between Biology and Environment
Pages 77-94

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From page 77...
... Chief among these is the emergence of the science of epigenetics, which synthesizes research findings from the social and biological sciences to understand the seamless and ongoing interaction between genes and the environment, with particular interest in cataloging the numerous environmental mechanisms comprising the nongenetic influ ­ ences of gene expression. In this context, "environment" encompasses all exposures or influences that can affect well-being or increase or limit oppor­ tunity, such as supportive parenting and stress.
From page 78...
... Adolescents exhibit heightened brain plasticity, making adolescence a sensitive period of development during which life-course trajectories can be changed for better or for worse. Because of the interactions between the brain, the body, and the environment and the plasticity of the adolescent brain, interventions to change developmental trajectories may be particularly effective during adolescence.
From page 79...
... Contrary to the traditional view that heredity is unchanging, current studies of gene-­ nvironment e interaction and epigenetics show that the ways in which heredity is expressed in behavior depends on environmental influences. The emerging field of epigenetics, therefore, studies biological processes not as primary causes of social outcomes but rather as mechanisms with contingent effects that depend on social structures, relationships, and interactions (McEwen and McEwen, 2017)
From page 80...
... can tag DNA and activate or repress genes. HISTONE TAIL GENE HISTONE TAIL DNA accessible, gene active Histone modification The binding of epigenetic factors to histone "tails" Histones are proteins around which HISTONE alters the extent to which DNA is wrapped around DNA can wind for compaction and DNA inaccessible, gene inactive histones and the availability of genes in the DNA gene regulation.
From page 81...
... . Rather, they are likely to be in a constant state of flux, determined by the various influences occurring at different times throughout the life course (Halfon et al., 2014, p.
From page 82...
... . Box 3-1 discusses the importance of sleep for adolescents and the ways in which environmental influences affect sleep and development.
From page 83...
... . Research suggests a neurobiological account for the observed connection between poor sleep quality and greater risk taking and delinquent behavior in ado lescence (Peach and Gaultney, 2013; Telzer et al., 2013)
From page 84...
... Even the social and biological transitions that occur during adulthood offer opportunities for plasticity to be exploited, so that interventions may be effective beyond the early childhood and adolescent years. RECIPROCAL INTERACTIONS BETWEEN BRAIN, BODY, AND ENVIRONMENT As discussed in the previous chapter, adolescence is a sensitive period of brain development, during which adolescents exhibit key developmental changes (Casey et al., 2008; Davidow et al., 2016; Steinberg, 2008)
From page 85...
... The hippocampal formation consists of three distinct parts: the dentate gyrus, the hippocampus proper, and the subiculum. • The dentate gyrus mediates memory processing of spatially based infor mation (Kesner, 2018)
From page 86...
... (In the example here we examine the effect of experiencing stress during adolescence; the pathways by which toxic stress in early childhood compromises the developing brain and body are discussed in Box 3-3.) The body and brain respond to environmental stressors through the biological stress response.
From page 87...
... . Insulin resistance is also associated over the life course with a subtype of major depression and is a risk factor for Alzheimer's disease (Rasgon and McEwen, 2016)
From page 88...
... This occurs when an individual is exposed to non-normative experiences that present greater adversity or threat than positive stress events do, such as a serious illness or injury or a parent's contentious divorce. These stressful events can result in tolerable stress when "protective adult relationships facilitate the child's adaptive coping and sense of control, reducing the physiologic stress response and promoting a return to baseline status" (Shonkoff and Garner, 2012, p.
From page 89...
... In the absence of preventative interventions to promote positive, adaptive neuroplasticity and health-promoting behavior and physiology, stressinduced changes in the brain are likely to increase a person's vulnerability to toxic stress and resulting allostatic overload (Eckenrode et al., 2017; Shonkoff et al., 2009)
From page 90...
... Although exposure to physical abuse and sexual abuse typically oc curs in childhood (with the median age at onset of child sexual abuse being 7.5 years of age (Tricket et al., 2011) , adolescence is a particularly vulnerable age for exposure to potentially traumatic events such as interpersonal violence, including dating violence, rape and sexual assault, and exposure to community violence.
From page 91...
... AMELIORATING EARLY LIFE ADVERSITIES IN ADOLESCENCE As discussed above and in Chapter 2, the heightened plasticity of the adolescent brain suggests that adolescence is a particularly sensitive period in which environmental influences may affect developmental trajectories, both positively and negatively, through a multitude of reciprocal interactions. In addition, this heightened sensitivity and responsiveness to environmental influences suggests that adolescence is a period when interventions can redirect and remediate maladaptation in brain structure and behavior that may have accumulated from earlier developmental periods.5 While preventing early life adversities is ideal,6 research shows that ameliorating and redirecting an unhealthy developmental trajectory remains possible during adolescence and later developmental periods.
From page 92...
... to examine young adults' whole hippocampal region as well as amygdala volume. Both the control population and the participants in the SAAF Program were largely from backgrounds of low socioeconomic status, with 46.3 percent living below poverty thresholds, a situation that normally forecasts diminishment in the volume of the left dentate gyrus, the CA3 hippocampal subfields, and the left ­ mygdala.
From page 93...
... Neurobiological processes can best be understood not as the cause of societal outcomes, but rather as mechanisms through which social structures, relationships, and interactions, t ­ogether with other environmental influences, effect changes in the individual person. In this way, environment can be said to "get under the skin." Because of the heightened plasticity of the adolescent brain and the interplay between genes and the environment, adolescence is a particularly sensitive period in which environmental influences may positively or negatively shape developmental trajectories through reciprocal interactions between the brain, the body, and the environment.
From page 94...
... Moreover, because environments and experiences interact with fundamental neurobiological developments, and because pubertal, neuro­ biological, cognitive, and psychosocial changes are occurring, adolescence represents a critical period of opportunity for the shaping of developmental trajectories. Adolescents are growing and learning within their environments, and each experience is an opportunity for adolescents to flourish and thrive.


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