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Developmental and Behavioral Theories
The field of pediatrics is dedicated to optimizing the growth and development of each child. Pediatricians require knowledge of normal growth, development, and behavior in order to effectively monitor children's progress, identify delays or abnormalities in development, help obtain needed services, and counsel parents and caretakers. To alter factors that increase or decrease risk, pediatricians need to understand how biologic and social forces interact within the parent–child relationship, within the family, and between the family and the larger society. Growth is an indicator of overall well-being, status of chronic disease, and interpersonal and psychologic stress. By monitoring children and families over time, pediatricians are uniquely situated to observe the interrelationships between physical growth and cognitive, motor, and emotional development. Observation is enhanced by familiarity with developmental and behavioral theories that inform one about typical patterns of development and provide guidance for prevention or intervention for behavior problems. Familiarity with theories of health behavior may assist in guiding patients and families in disease management and wellness care.
Biopsychosocial Model and Ecobiodevelopmental Framework: Models of Development
The medical model presumes that a patient presents with signs and symptoms and a physician focuses on diagnosing and treating diseases of the body. This model neglects the psychologic aspect of a person who exists in the larger realm of the family and society. In the biopsychosocial model , societal and community systems are simultaneously considered along with more proximal systems that make up the person and the person's environment ( Fig. 18.1 ). A patient's symptoms are examined and explained in the context of the patient's existence. This basic model can be used to understand health and both acute and chronic disease.
With the advances in neurology, genomics (including epigenetics), molecular biology, and the social sciences, a more accurate model, the ecobiodevelopmental framework , has emerged. This framework emphasizes how the ecology of childhood (social and physical environments) interacts with biologic processes to determine outcomes and life trajectories. Early influences, particularly those producing toxic levels of stress , affect the individual through modification of gene expression, without change in DNA sequencing. These epigenetic changes , such as DNA methylation and histone acetylation (see Chapter 100 ), are influenced by the early life experiences (the environment). Stress responses may produce alterations in brain structure and function, leading to disruption of later coping mechanisms. These changes will produce long-lasting effects on the health and well-being of the individual and may be passed on to future generations ( Fig. 18.2 ).
Critical to learning and remembering (and therefore development) is neuronal plasticity , which permits the central nervous system to reorganize neuronal networks in response to environmental stimulation, both positive and negative. An overproduction of neuronal precursors eventually leads to about 100 billion neurons in the adult brain. Each neuron develops on average 15,000 synapses by 3 yr of age. During early childhood, synapses in frequently used pathways are preserved, whereas less-used ones atrophy, a process termed “pruning.” Changes in the strength and number of synapses and reorganization of neuronal circuits also play important roles in brain plasticity. Increases or decreases in synaptic activity result in persistent increases or decreases in synaptic strength. Thus experience ( environment ) has a direct effect on the physical and therefore functional properties of the brain. Children with different talents and temperaments (already a combination of genetics and environment) further elicit different stimuli from their (differing) environments.
Periods of rapid development generally correlate with periods of great changes in synaptic numbers in relevant areas of the brain. Accordingly, sensory deprivation during the time when synaptic changes should be occurring has profound effects. For example, the effects of strabismus leading to amblyopia in one eye may occur quickly during early childhood; likewise, patching the eye with good vision to reverse amblyopia in the other eye is less effective in late childhood (see Chapter 641 ). Early experience is particularly important because learning proceeds more efficiently along established synaptic pathways.
Early traumatic experiences modify the expression of stress mediators (in particular the hypothalamic-pituitary-adrenal axis) and neurotransmitters, leading to changes in brain structure and function. These effects may be persistent, leading to alterations and dysfunction in the stress response throughout life. Chronic stress has negative effects on cognitive functions, including memory and emotional regulation. Positive and negative experiences do not determine the ultimate outcome, but shift the probabilities by influencing the child's ability to respond adaptively to future stimuli. The plasticity of the brain continues into adolescence, with further development of the prefrontal cortex, which is important in decision-making, future planning, and emotional control; neurogenesis persists in adulthood in certain areas of the brain.
Biologic Influences
Biologic influences on development include genetics, in utero exposure to teratogens, the long-term negative effects of low birthweight (neonatal morbidities plus increased rates of subsequent adult-onset obesity, coronary heart disease, stroke, hypertension, and type 2 diabetes), postnatal illnesses, exposure to hazardous substances, and maturation. Adoption and twin studies consistently show that heredity accounts for approximately 40% of the variance in IQ and in other personality traits, such as sociability and desire for novelty, whereas shared environment accounts for another 50%. The negative effects on development of prenatal exposure to teratogens, such as mercury and alcohol, and of postnatal insults, such as meningitis and traumatic brain injury, have been extensively studied (see Chapters 115 and 120 ). Any chronic illness can affect growth and development, either directly or through changes in nutrition, parenting, school attendance, or peer interactions.
Most children follow similar motor developmental sequences; the age at which children walk independently is similar around the world, despite great variability in child-rearing practices. The attainment of other skills, such as the use of complex sentences, is less tightly bound to a maturational schedule. Maturational changes also generate behavioral challenges at predictable times. Decrements in growth rate and sleep requirements around 2 yr of age often generate concern about poor appetite and refusal to nap. Although it is possible to accelerate many developmental milestones (toilet-training a 12 mo old or teaching a 3 yr old to read), the long-term benefits of such precocious accomplishments are questionable.
In addition to physical changes in size, body proportions, and strength, maturation brings about hormonal changes. Sexual differentiation, both somatic and neurologic, begins in utero. Both stress and reproductive hormones affect brain development as well as behavior throughout development. Steroid production by the fetal gonads leads to differences in brain structures between males and females.
Temperament describes the stable, early-appearing individual variations in behavioral dimensions, including emotionality (crying, laughing, sulking), activity level, attention, sociability, and persistence. The classic theory proposes 9 dimensions of temperament ( Table 18.1 ). These characteristics lead to 3 common constellations: (1) the easy, highly adaptable child, who has regular biologic cycles; (2) the difficult child, who is inflexible, moody, and easily frustrated; and (3) the slow-to-warm-up child, who needs extra time to adapt to new circumstances. Various combinations of these clusters also occur. Temperament has long been described as biologic or “inherited.” Monozygotic twins are rated by their parents as temperamentally similar more often than are dizygotic twins. Estimates of heritability suggest that genetic differences account for approximately 20–60% of the variability of temperament within a population. The remainder of the variance is attributed to the child's environment. Maternal prenatal stress and anxiety is associated with child temperament, possibly through stress hormones. However, certain polymorphisms of specific genes moderate the influence of maternal stress on infant temperament. Children who are easily frustrated, fearful, or irritable may elicit negative parental reactions, making these children even more susceptible to negative parenting behaviors and to poor adjustment to adversity. Longitudinal twin studies of adult personality indicate that changes in personality over time largely result from nonshared environmental influences, whereas stability of temperament appears to result from genetic factors.
Table 18.1
Temperamental Characteristics: Descriptions and Examples
Based on data from Chess S, Thomas A: Temperament in clinical practice, New York, 1986, Guilford.
| CHARACTERISTIC | DESCRIPTION | EXAMPLES * |
|---|---|---|
| Activity level | Amount of gross motor movement | “She's constantly on the move.” “He would rather sit still than run around.” |
| Rhythmicity | Regularity of biologic cycles | “He's never hungry at the same time each day.” “You could set a watch by her nap.” |
| Approach and withdrawal | Initial response to new stimuli | “She rejects every new food at first.” “He sleeps well in any place.” |
| Adaptability | Ease of adaptation to novel stimulus | “Changes upset him.” “She adjusts to new people quickly.” |
| Threshold of responsiveness | Intensity of stimuli needed to evoke a response (e.g., touch, sound, light) | “He notices all the lumps in his food and objects to them.” “She will eat anything, wear anything, do anything.” |
| Intensity of reaction | Energy level of response | “She shouts when she is happy and wails when she is sad.” “He never cries much.” |
| Quality of mood | Usual disposition (e.g., pleasant, glum) | “He does not laugh much.” “It seems like she is always happy.” |
| Distractibility | How easily diverted from ongoing activity | “She is distracted at mealtime when other children are nearby.” “He doesn't even hear me when he is playing.” |
| Attention span and persistence | How long a child pays attention and sticks with difficult tasks | “He goes from toy to toy every minute.” “She will keep at a puzzle until she has mastered it.” |
* Typical statements of parents, reflecting the range for each characteristic from very little to very much.
The concept of temperament can help parents understand and accept the characteristics of their children without feeling responsible for having caused them. Children who have difficulty adjusting to change may have behavior problems when a new baby arrives or at the time of school entry. In addition, pointing out the child's temperament may allow for adjustment in parenting styles. Behavioral and emotional problems may develop when the temperamental characteristics of children and parents are in conflict. For example, if parents who keep an irregular schedule have a child who is not readily adaptable, behavioral difficulties are more likely than if the child has parents who have predictable routines.
Psychologic Influences: Attachment and Contingency
The influence of the child-rearing environment dominates most current models of development. Infants in hospitals and orphanages, devoid of opportunities for attachment, have severe developmental deficits. Attachment refers to a biologically determined tendency of a young child to seek proximity to the parent during times of stress and also to the relationship that allows securely attached children to use their parents to reestablish a sense of well-being after a stressful experience. Insecure attachment may be predictive of later behavioral and learning problems.
At all stages of development, children progress optimally when they have adult caregivers who pay attention to their verbal and nonverbal cues and respond accordingly. In early infancy, such contingent responsiveness to signs of overarousal or underarousal helps maintain infants in a state of quiet alertness and fosters autonomic self-regulation. Contingent responses (reinforcement depending on the behavior of the other) to nonverbal gestures create the groundwork for the shared attention and reciprocity that are critical for later language and social development. Children learn best when new challenges are just slightly more difficult than what they have already mastered, a degree of difficulty dubbed the “zone of proximal development.” Psychologic forces, such as attention problems (see Chapter 49 ) or mood disorders (see Chapter 39 ), will have profound effects on many aspects of an older child's life.
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