Abundant research in psychology, human development, and other fields has shown that events and circumstances early in peoples’ lives influence future decisions, life events, and life circumstances—or what is called the life course trajectory. People who use drugs typically begin doing so during adolescence or young adulthood (see “Adolescent Drug Use”), but the ground may be prepared for drug use much earlier, by circumstances and events that affect the child during the first several years of life and even before birth.
The first, overarching principle drawn from the research reviewed for this resource is that intervening early in childhood can alter the life course trajectory of children in a positive direction.
Early childhood, considered in this resource to include the prenatal period through age 8, includes the following developmental periods:
- Prenatal Period (conception and birth)
- Infancy and Toddlerhood (birth to 3 years)
- Preschool (ages 3 through 5 years)
- Transition to School (ages 6 through 8 years)*
*The transition to school period is actually part of the middle childhood and early adolescence period (6 to 13 years) but is addressed separately in this resource because it is a major and significant transition in the child’s development. The middle childhood period is followed by adolescence (ages 13 to 18). The age range for the interventions that form the basis for the principles of prevention described in this resource is prenatal through 8 years.
- Adolescent Drug Use
Collection of data from the National Survey of Drug Use and Health (NSDUH) on age at first use of illegal drugs across the U.S. begins at age 12 years, with data from 2014 indicating that 3.4 percent of 12- to 13-year-old children have used an illegal drug in the past month (including inappropriate use of prescription drugs), 2.1 percent are current alcohol users, and 1.1 percent are current tobacco users (CBHSQ, 2015). In 2015, NIDA’s annual Monitoring the Future (MTF) survey of adolescent drug use and attitudes showed that, by the time they are seniors, 64 percent of high school students have tried alcohol, almost half have taken an illegal drug, 31 percent have smoked a cigarette, and 18 percent have used a prescription drug for a nonmedical purpose (Johnston et al., 2016).
What does the life course perspective show about risk for drug abuse and how to prevent it?
The period of development covered in this guide is characterized by rapid orderly progressions of normal patterns of physical, cognitive, emotional, and social development. This development is marked by important transitions between developmental periods and the achievement of successive developmental milestones (see “Life Transitions” and “Developmental Milestones”). How successfully or unsuccessfully a child meets the demands and challenges arising from a given transition, and whether the child meets milestones on an appropriate schedule, can affect his or her future course of development, including risk for drug abuse or other mental, emotional, or behavioral problems during adolescence.
A variety of factors, known as risk factors, can interrupt or interfere with unfolding developmental patterns in all of these periods and, especially, in the transitions between them. Prevention interventions designed specifically for early developmental periods can address these risk factors by building on existing strengths of the child and his or her parents (or other caregivers) and by providing skills (e.g., general parenting skills and specific skills like managing aggressive behavior), problem-solving strategies, and support in areas of the child’s life that are underdeveloped or lacking.
Life events or transitions represent points during which the individual is in a period of change, and they are sometimes called sensitive, critical, or vulnerable periods (Brazelton, 1992; Bornstein, 1989). Although vulnerability can occur at many points along the life course, it tends to peak at critical life transitions, which present risks for substance abuse as well as opportunities for intervention. Thus transitions such as pregnancy, birth, or entering preschool or elementary school are prime opportunities to introduce skills, knowledge, and competencies to facilitate development during those transitions. Therefore, interventions are often designed to be implemented around periods of transition.
The life transitions diagram points to life course periods, contexts, and transitions or life events that together contribute to the development of the child from the prenatal period through young adulthood. (The life course continues through to the end of life, but this resource focuses on just the early years.)
- Life Transitions
Vulnerability to the risk factors for problems such as substance abuse can occur throughout the life course, but it tends to peak during critical life transitions. Transitions may be biological, such as puberty, or they may involve entering a new environmental context, such as attending school for the first time. How a child responds and adapts to these events is influenced by his or her cognitive, emotional, and social development at that point in time as well as past history, family relationships, and the surrounding world. Other transitions, such as parental divorce or military deployment of a parent, may not be predictably linked to a child’s development, but these events or circumstances still require the child to adapt successfully (for instance to new people or new contexts). Because of their introduction of new potential risk factors, transitions are sometimes called sensitive, critical, or vulnerable periods, and they are prime opportunities for preventive intervention.
The figure below illustrates the development/life course trajectory from the prenatal period through young adulthood, indicating the periods of transition and life change that could represent both times of risk and periods where intervention could be of greatest benefit
[Text description - Chart illustrating the spheres of influence through the stages of life: early childhood, middle childhood, adolescence, and early adulthood. Also shown are the developmental periods: prenatal, infancy, toddlerhood, and preschool, which all fall within early childhood, and puberty, which goes from the end of middle childhood through part of adolescence. Transition periods include birth, transition to elementary school, dating, leaving home, vocational choice, marriage, early childhood rearing, and parent of child entering school. The spheres of influence include: genes/biology from prenatal through early adulthood; maternal health from prenatal through infancy; family from prenatal through early adulthood; community from prenatal through early adulthood; classroom from preschool to leaving home; peers from preschool through early adulthood; intimate pair/family from the beginning to the end of early adulthood; and work from the beginning to the end of early adulthood.]
- Developmental Milestones
Developmental milestones refer to particular physical, cognitive, social, or emotional capabilities that are ordinarily acquired within a certain age range. For example, most infants crawl around 9 months and walk by 12 to 15 months; most toddlers can speak one- and two-word phrases between ages 1 and 2; and so on (see www.cdc.gov/ncbddd/actearly/milestones/index.html). Over the course of development, these emerging capabilities generally trigger changes in other people’s expectations and responses—for instance, upon entering elementary school, teachers will expect children to be able to sit and be attentive. Achieving milestones within the expected time frame is an important signal that development is occurring in the expected manner and timeframe, and offers protection against risk factors for substance abuse and other problems later in development. Failure to achieve important milestones may indicate the need for early intervention.
This does not mean that a child who is well below average on a milestone will not eventually achieve that milestone (or will necessarily develop later problems); milestones can be achieved later in development, albeit with greater difficulty. Part of what makes it possible to achieve a milestone at a later time is the ability of the brain to change, adapt, and reorganize. This type of brain activity is called plasticity, and the brain remains plastic to some degree throughout life (Kellam & Rebok, 1992; Leighton et al., 1963; Weiss, 1949). However, very young children have the greatest neurological flexibility and potential for learning new skills and behaviors; brain structure stabilizes with age and it becomes increasingly difficult to alter (see “The Developing Brain, 0 to 8 Years”).
What are the major influences on a child’s early development?
The changes unfolding throughout a child’s development are influenced by a complex combination of factors. One of them is the genes the child inherits from his or her biological parents. Genetic factors play a substantial role in an individual’s development through the course of life, influencing a person’s abilities, personality, physical health, and vulnerability to risk factors for behavioral problems like substance abuse. But genes are only part of the story.
Another very important factor is the environment, or the contexts into which the child is born and in which the child grows up. The family/home environment is the context that most directly influences the young child’s early development and socialization (see “Socialization”). This includes quality of parenting and other parenting influences such as genetic factors and family functioning. Also, siblings, if present, can influence a child’s development and adjustment (e.g., internalizing and externalizing behaviors and substance use, as well as positive behaviors) (Dunn, 2005; Feinberg et al., 2013; Kramer & Conger, 2009; Pike et al., 2005). These influences may result from shared environmental experiences and interactions with parenting and other family factors (Burt et al., 2010; Neiderhiser et al., 2013). But conditions at home are also influenced by wider physical, social, economic, and historical realities—such as the family’s socio-economic status and the affluence and safety (or lack thereof) of the community in which the family lives. As the child grows older and enters school, these wider environmental contexts influence him or her more directly.
Socialization refers to a process of acquiring and internalizing the behaviors, norms, and beliefs of the individual’s society. It is a process that occurs across the course of development. During the early childhood period, both internal processes (such as learning style, attention, information processing) and the sum total of the child’s social experiences in family, school, and community contexts affect socialization.
What follows is an overview of the developmental influences and changes taking place during specific periods of early childhood development.
The genes, biological capacities, and innate temperament that children are born with inform the way they interact with the environment and people in it. Development is shaped by a combination of genetic and environmental factors (see “The Developing Brain, 0 to 8 Years”).
Even before a child is born, the context or environment plays an important role in development. It has long been known, for example, that if the mother smokes, drinks alcohol, or uses other drugs during her pregnancy, these substances can enter the body of the developing fetus and have significant effects on the development of the body and brain, and these effects may become risk factors for substance use later in the child’s life (see “Risk and Protective Factors” for more information). There is also emerging evidence that both parents’ past histories of substance use may affect their children via changes to gene expression (see “Epigenetics”). Also, poor nutrition during the prenatal period can have adverse effects on the development of the child’s brain (National Research Council and Institute of Medicine, 2000; Prado & Dewey, 2014).
- The Developing Brain, 0 to 8 Years
The brain is a dense network of nerve cells (neurons) and glial cells that support the neurons in various ways. The neurons are organized in circuits that control everything people think and do—from learning and movement to language, sensing, feeling, and exerting control over emotions and behaviors. The brain’s development begins soon after conception, when cells in the embryo begin to form the basic structure of the central nervous system including the brain and spinal cord. How it develops is influenced by genetics, aspects of the environment such as nutrition and social interactions, and life experiences. The relative importance of these influences shifts over the course of life, and at any point they may interact in complex ways. For example, a particular genetic factor might impede the process of a child’s language development; but if the child is born into a family where parents regularly talk or read to the child, it may foster language development and act to offset those genetic influences. Brain development is not simply the growth of new nerve cells and formation of synaptic connections (connections between neurons). Early in life, there is an overproduction of synaptic connections, and over the course of childhood and adolescence a process called pruning reduces the number of those connections. Connections that are used frequently become strengthened; those that are not are eliminated. For example, children are born with the capacity to understand and replicate sounds of all languages; however, over the course of development these abilities become specific to the language or languages to which they are exposed. Thus the neural connections that would allow further language development diminish in the middle childhood years.
Across childhood and adolescence, the cortex (the outer layer of the brain) matures at different speeds, as measured by its overall volume, its thickness, its surface area, and other characteristics that correspond to its functioning. Generally, areas at the back and sides of the brain that process sensory information (e.g., vision, hearing, and all types of body sensations) finish developing earliest, during childhood; frontal cortical areas, which handle emotional and behavioral control and other higher order executive functions, are the last to finish developing—only reaching maturity in early adulthood. Boys’ and girls’ brains differ in their pattern of brain maturation, with peak changes in cortical volume and surface area typically occurring later in boys (around age 10) than in girls (around age 8) (Raznahan et al., 2011).
The proportional genetic and environmental influences on various aspects of brain development are not the same across all brain regions. Recent twin studies have shown, for example, that variations in the thickness of the frontal cortex are more attributable to genetic factors than thickness of other areas of the cortex (Schmitt et al., 2014). Also, the relative influence of environmental and genetic factors in brain development shifts across the first three decades of life: The environment exerts its greatest proportional impact in early childhood and gradually lessens, relative to genetic influences, across later childhood and adolescence. This provides an important genetic and neurobiological rationale for intervening in early childhood, when changes in the individual’s environment can have the greatest long-term impact.
Recent research in the emerging field of epigenetics, or the study of environmental influences on the way genes are expressed, suggests that both the mother’s and father’s past history of substance use, even before conception, may influence the health of their children. Studies in experimental animals have shown that substance use may cause changes in gene expression in a father’s sperm and a mother’s egg cells, which could then affect the growth and brain development of offspring, influencing their response to substances of abuse (Novikova et al., 2008; Vassoler et al., 2013; Szutorisz et al., 2014). Future studies will determine if this also occurs in humans.
Infancy and Toddlerhood
Once the child is born, factors that contribute to the child’s development include the quality of the nutrition and health care provided by the mother and other caregivers, the personality fit between infant and caregivers, and the ability of the caregivers to provide warmth and support. The child also plays a more active role in shaping his or her environmental context (see “Influence is not Just a One-Way Street, below”).
Influence is not Just a One-Way Street
Within moments after birth, the infant’s personality and overall health can influence the parent-child relationship and physical environment in significant ways. As the child grows older, his or her unfolding personality and needs influence the family environment, school environment, and wider social contexts, which in turn exert an influence on the child and others in the same surroundings.
Over the months following birth, the child adapts to and integrates into the surrounding world as he or she makes further developmental gains, including ongoing brain development. Through practice, the child ideally becomes proficient at basic skills using limited but growing sensory, motor, cognitive, and social capacities, meeting basic milestones along the way. As the infant learns to distinguish self from others, he or she instinctively focuses attention on the primary caregiver(s), usually parents.
For optimal positive development to occur, the primary caregiver(s) must consistently meet the child’s needs, be nurturing, provide a predictable schedule, and provide developmentally appropriate stimulation. The closeness of the parent-child relationship during this early period provides a context for the child’s development and his or her expectations about the world as well as for secure attachment to his or her caregiver(s). Secure attachment is one of the most crucial factors leading to healthy socialization and self-regulation, which are major protective factors against drug use and other behavioral problems.
Throughout early childhood, even when the child enters preschool or attends day care, the family remains the most important context for development. Parents play a number of roles in the development of a young child’s social, emotional, and cognitive competence, including establishing the structure and routines for parent-child interactions; maintaining a sensitive, warm, and responsive relationship style; and providing instructional practices and experiences that help the child acquire necessary developmental skills. Development of motor abilities and language skills are important in the preschool period, influencing the child’s growing independence.
When a nurturing, responsive relationship does not exist, elevated levels of stress hormones can impede a child’s healthy brain development (Debellis & Zisk, 2014; Thompson, 2014). Moreover, when a caregiver cannot provide attention and nurturing because of a history of trauma, chronic stress, and/or mental health problems, the child is more likely to develop behavioral, social, emotional, or cognitive problems (Madigan et al., 2012; Delker et al., 2014). Likewise, impaired judgment related to substance use can reduce a parent’s ability to create a warm, supportive environment for the child (Barnard & McKeganey, 2004; Lam et al., 2007). Child abuse and neglect, social isolation due to illness or disability, and lack of constancy in the primary caregiver (as in the case of a child in institutionalized care) are also linked to growth (including brain growth and neuronal connectivity), cognitive, motor, social, and emotional problems (see for example, Behen et al., 2009; Martins et al., 2013; McCall, 2013; Koss et al., 2014). Many of the prevention interventions discussed in this guide are aimed at facilitating constant, nurturing, responsive caregiving to reduce risk and prevent child behavior problems.
Transition to School
As the child grows older, new transitions and associated challenges occur. A major transition for young children is beginning elementary school. Even children who attended preschool or had been in day care can find the rules for behavior and academic requirements associated with elementary school difficult to adapt to and achieve. Readiness for school is something that occurs over time with experience and practice. Early intervention can help parents and schools assist children through this transition. Once in elementary school, teachers can help children to adjust by providing positive classroom management.
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