CHAPTER 2 Behavioral Development
A variety of processes are encompassed in growth and development: the formation of tissue; an increase in physical size; the progressive increases in strength and ability to control large and small muscles (gross motor and fine motor development); and the advancement of complexities of thought, problem solving, learning, and verbal skills (cognitive and language development). There is a systematic approach for tracking neurologic development and physical growth in infants, because attainment of milestones is orderly and predictable. However, a wide range exists for normal achievement. The mastering of a particular skill often builds on the achievement of an earlier skill. Delays in one developmental domain may impair development in another (Gessel and Amatruda, 1951). For example, immobility caused by a neuromuscular disorder prevents an infant from exploration of the environment, thus impeding cognitive development. A deficit in one domain might interfere with the ability to assess progress in another area. For example, a child with cerebral palsy who is capable of conceptualizing matching geometric shapes but does not have the gross or fine motor skills necessary to perform the function could erroneously be labeled as developmentally delayed.
Prenatal growth
The most dramatic events in growth and development occur before birth. These changes are overwhelmingly somatic, with the transformation of a single cell into an infant. The first eight weeks of gestation are known as the embryonic period and encompasses the time when the rudiments of all of the major organs are developed. This period denotes a time that the fetus is highly sensitive to teratogens such as alcohol, tobacco, mercury, thalidomide, and antiepileptic drugs. The average embryo weighs 9 g and has a crown-to-rump length of 5 cm. The fetal stage (more than 9 weeks’ gestation) consists of increases in cell number and size and structural remodeling of organ systems (Moore, 1972).
During the third trimester, weight triples and length doubles as body stores of protein, calcium, and fat increase. Low birth weight can result from prematurity, intrauterine growth retardation (small for gestational age, SGA) or both. Large-for-gestational-age (LGA) infants are those whose weight is above the 90th percentile at any gestational age. Deviations from the normal relationship of infant weight gain with increasing gestational age can be multifactorial. Potential causes include maternal diseases (e.g., diabetes, pregnancy-induced hypertension, and seizure disorders), prenatal exposure to toxins (e.g., alcohol, drugs, and tobacco), fetal toxoplasmosis-rubella-cytomegalovirus-herpes simplex-syphilis (TORCHES) infections, genetic abnormalities (e.g., trisomies 13, 18, and 21), fetal congenital malformations (e.g., cardiopulmonary or renal malformations), and maternal malnutrition or placental insufficiency (Kinney and Kumar, 1988).
Postnatal growth
Growth milestones are the most predictable, taking into context each child’s specific genetic and ethnic influences (Johnson and Blasco, 1997). It is essential to plot the child’s growth on gender- and age-appropriate percentile charts. Charts are now available for certain ethnic groups and genetic syndromes such as Trisomy 21 and Turner’s syndrome. Deviation from growth over time across percentiles is of greater significance for a child than a single weight measurement. For example, an infant at the fifth percentile of weight for age may be growing normally, may be failing to grow, or may be recovering from growth failure, depending on the trajectory of the growth curve.
Developmental assessment
Milestones are useful indicators of mental and physical development and possible deviations from normal. It should be emphasized that milestones represent the average for children to attain and that there can be variable rates of mastery that fall into the normal range. An acceptable developmental screening test must be highly sensitive (detect nearly all children with problems); specific (not identify too many children without problems); have content validity, test-retest, and interrater reliability; and be relatively quick and inexpensive to administer. The most widely used developmental screening test is the Denver Developmental Screening Test (DDST), which provides a pass/fail rating in four domains of developmental milestones: gross motor, fine motor, language, and personal-social. The original DDST was criticized for underidentification of children with developmental disabilities, particularity in the area of language. The reissued DDST-II is a better assessment for language delays, which is important because of the strong link between language and overall cognitive development. Table 2-1 lists the prevalence of some common developmental disabilities (Levy and Hyman, 1993).
TABLE 2-1 Prevalence of Developmental Disabilities
| Condition | Prevalence per 1000 |
| Cerebral palsy | 2-3 |
| Visual impairment | 0.3-0.6 |
| Hearing impairment | 0.8-2 |
| Mental retardation | 25 |
| Learning disability | 75 |
| Attention deficit hyperactivity disorder | 150 |
| Behavioral disorders | 60-130 |
| Autism | 9-10 |
Motor development
Primitive Reflexes
The earliest motor neuromaturational markers are primitive reflexes that development during uterine life and generally disappear between the third and sixth months after birth. Newborn movements are largely uncontrolled, with the exception of eye gaze, head turning, and sucking. Development of the infant’s central nervous system involves strengthening of the higher cortical center that gradually takes over function of the primitive reflexes. Postural reflexes replace primitive reflexes between three and six months of age as a result of this development (Schott and Rossor, 2003). These reactions allow children to maintain a stable posture even if they are rapidly moved or jolted (Box 2-1).
Box 2-1 Definitions of Primitive Reflexes
Postural reflexes support control of balance, posture, and movement in a gravity-based environment. The protective equilibrium response can be elicited in a sitting infant by abruptly pushing the infant laterally. The infant will extend the arm on the contralateral side and flex the trunk toward the side of the force to regain the center of gravity (Fig. 2-1). The parachute response develops around 9 months and is a response to a free-fall motion, where the infant extends the extremities in an outward motion to distribute weight over a broader area. Postural reactions are markedly slow in appearance in the infant who has central nervous system damage. Children who fail to gain postural control continue to display traces of primitive reflexes. They also have difficulty with control of movement affecting coordination, fine and gross motor development, and other associated aspects of learning, including reading and writing. Table 2-2 is a list of the average times of appearance and disappearance of the more common primitive reflexes.
| Reflex | Present by (Months) | Gone by (Months) |
| Automatic stepping | Birth | 2 |
| Crossed extension | Birth | 2 |
| Galant | Birth | 2 |
| Moro | Birth | 3-6 |
| Palmar | Birth | 4-6 |
| Asymmetric tonic neck (“fencing”) | 1 | 4-6 |
| Landau | 3 | 12-24 |
| Derotational head righting | 4 | Persists |
| Protective equilibrium | 4-6 | Persists |
| Parachute | 8-9 | Persists |
Gross Motor Skills
One principle in neuromaturational development during infancy is that it proceeds from cephalad to caudad and proximal to distal. Thus, arm movement comes before leg movement (Feldman, 2007). The upper extremity attains increasing accuracy in reaching, grasping, transferring, and manipulating objects. Gross motor development in the prone position begins with the infant tightly flexing the upper and lower extremities and evolves to hip extension while lifting the head and shoulders from a table surface around 4 to 6 months of age. When pulled to a sitting position, the newborn has significant head lag, whereas the 6-month-old baby, because of development of muscle tone in the neck, raises the head in anticipation of being pulled up.
Rolling movements start from front to back at approximately 4 months of age as the muscles of the lower extremities strengthen. An infant begins to roll from back to front at about 5 months. The abilities to sit unsupported (about 6 months old) and to pivot while sitting (around 9 to 10 month of age) provide increasing opportunities to manipulate several objects at a time (Needleman, 1996). Once thoracolumbar control is achieved and the sitting position mastered, the child focuses motor development on ambulation and more complex skills. Locomotion begins with commando-style crawling, advances to creeping on hands and knees, and eventually reaches pulling to stand around 9 months of age, with further advancement to cruising around furniture or toys. Standing alone and walking independently occur around the first birthday. Advanced motor achievements correlate with increasing myelinization and cerebellum growth. Walking several steps alone has one of the widest ranges for mastery of all of the gross motor milestones and occurs between 9 and 17 months of age. Milestones of gross motor development are presented in Table 2-3 and Figure 2-2. The accomplishment of locomotion not only expands the infant’s exploratory range and offers new opportunities for cognitive and motor growth, but it also increases the potential for physical dangers (Vaughan, 1992).
TABLE 2-3 Cognitive and Language Communication Skills Development
| Average Age of Attainment (Months) | Cognitive | Language Communication |
| 2 | Stares briefly at area when object is removed | Smiles in response to face or voice |
| 4 | Stares at own hand | Monosyllabic babble |
| 8 |
