Neurodevelopment (page 2)
Concurrently with the developmental changes observed across the motor, language, cognitive, and social domains, underlying neurodevelopmental changes are occurring. In fact, one of the primary reasons for the observed developmental changes seen from birth through the preschool years is associated brain development. Needless to say, it is rapidly developing during this time period and fuels many of the wonderful changes that can be seen in children as they move through the infant, toddler, and preschool years. It is important for the early interventionist to have a working understanding of how the brain contributes to the various behaviors exhibited by a child.
While a review of the neurological development of various brain structures and their associated functions is beyond the scope of this book (see Swaiman, Ashwal, & Ferrier, 2006, for a comprehensive examination of this topic), it is important to note that brain development begins in the womb with an overproduction of neurons. During that time period it is extremely susceptible to negative factors (e.g., maternal illness) but as well as to positive factors (good maternal health and nutrition). At birth, the brain has the neurons in the correct places, in general, and it weighs approximately 25% of its final adult weight. In healthy children, brain volume increases steadily until about age 10 to 12 years, with about 75% of the adult brain weight occurring by 24 months; by age 3 it is closer to its mature size than any other body part (Puckett & Black, 2004); and by age five years it has attained approximately 96% of its adult size and weight (Carmichael, 1990; Pfefferbaum et al., 1994). This brain growth is largely fueled by the rapid branching and increased connections among neurons as well as the increased myelination that occurs on the axons. The myelination process is critical not only to increasing the capacity of brain structures, but also to increasing the rate of speed with which information is communicated along the axons. Conversely, while the brain is growing and maturing, and concomitant behaviors are changing, the brain also is striving to be more efficient. In this regard, the brain also engages in a process called pruning, wherein ineffective and/or inefficient neuronal connections are eliminated. This process begins around age 4 years, but will continue throughout much of childhood and young adulthood (Whitaker, Bub, & Leventer, 1981). Epstein (2001) has noted that many of these changes in neurodevelopment actually seem to coincide with Piaget’s stages of cognitive development.
Suffice it to say that certain aspects of the overall anatomy of very young children make them more vulnerable to the negative effects of neurological insult and injury. For example, with respect to traumatic brain injury (TBI), infants and toddlers have proportionally larger heads than older children and adults. The disproportional distributions of the head, neck, and trunk result in TBI impacting the bodies and brains of very young children differently than older children or adults (Ewings-Cobb et al., 1995; Keenan, Hooper, Wetherington, Nocera, & Runyan, 2007). Neck muscles may not yet be strong enough to protect the head and brain stem from injury as well as they would in older individuals. The developing skulls of infants have soft membranes (i.e., sutures and fontanelles) that differ significantly from the rigid skulls of adults, contributing to the differential impact of a trauma to the brain (Goldsmith & Plunkett, 2004). Other characteristics of the skull and brain that make infants especially susceptible to injury are the skull’s thinness and pliability, the brain’s softness, a lack of a myelin sheath for many axons, a flatter base of the skull, and immature neck muscles (Case, Graham, Corey-Handy, Jentzen, & Monteleone, 2001). These characteristics, in tandem with a subsequent insult or injury, can disrupt the developmental trajectories of a variety of skills and abilities which, in turn, may negatively affect the development of motor, language, cognitive, social-emotional, and adaptive behaviors and learning.
In addition to trauma-induced neurological differences, sometimes neurodevelopment is simply different, but different enough to create problems with attention and behavior (e.g., attention deficit-hyperactivity disorder), language (e.g., specific language disorder), and related learning (e.g., learning disabilities, intellectual disabilities, autism). As we move into the next section, Factors Affecting Development, think about how brain development and function may be a major part of the behaviors that are described in young children. As an exercise, you may want to do some research to see what brain functions might be affected by the various factors that will be discussed. Indeed, there is a rapidly growing body of literature in that regard, one that should be of interest to the early interventionist in increasing understanding of overall child development.
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