Читать книгу Lifespan Development - Tara L. Kuther - Страница 210

The brain comprises different structures with differing functions, located across four lobes. The various parts of the brain work together, but as shown in Figure 4.5, each lobe is specialized to a certain extent. In addition, the brain comprises two hemispheres that are joined by a thick band of neural fibers known as the corpus collosum. Although all four lobes appear on both hemispheres, the hemispheres are not identical. The right and left hemispheres are specialized for different functions, known as lateralization. For most people, language is governed by the left hemisphere. Each hemisphere of the brain (and the parts of the brain that comprise each hemisphere) is specialized for particular functions and becomes more specialized with experience. This process of the hemispheres becoming specialized to carry out different functions is called lateralization (Duboc, Dufourcq, Blader, & Roussigné, 2015).

Lateralization (“of the side” in Latin) begins before birth and is influenced both by genes and by early experiences (Young, 2016). For example, in the womb, most fetuses face toward the left, freeing the right side of the body, which permits more movement on that side and the development of greater control over the right side of the body (Previc, 1991). In newborns, the left hemisphere tends to have greater structural connectivity and efficiency than the right—more connections and pathways suggesting that they are better able to control the right side of their bodies (Ratnarajah et al., 2013). Newborns tend to have slightly better hearing from their right ear (Ari-Even Roth, Hildesheimer, Roziner, & Henkin, 2016). Infants generally display a hand preference, usually right, and their subsequent activity makes the hand more dominant because experience strengthens the hand and neural connections and improves agility. In this way, one hemisphere becomes stronger and more adept, a process known as hemispheric dominance. Most adults experience hemispheric dominance, usually with the left hemisphere dominating over the right, making about 90% of adults in Western countries right-handed (Duboc et al., 2015).

Although the left and right hemispheres are implicated for different functions, some researchers note that a strict right/spatial and left/language dichotomy is overly simplistic (Vilasboas, Herbet, & Duffau, 2017). Despite lateralization, the two hemispheres interact in a great many complex ways to enable us to think, move, create, and exercise our senses (Efron, 1990; Richmond, Johnson, Seal, Allen, & Whittle, 2016; Springer & Deutsch, 1998). Complex activities such as thinking and problem solving involve communication between both hemispheres of the brain (Turner, Marinsek, Ryhal, & Miller, 2015). The corpus callosum, a collection of 250 to 800 million neural fibers, connects the left and right hemispheres of the brain, permitting them to communicate and coordinate processing (Banich & Heller, 1998). During early childhood, the corpus callosum grows and begins to myelinate, permitting the two halves of the brain to communicate in more sophisticated and efficient ways and to act as one, enabling the child to execute large and fine motor activities such as catching and throwing a ball or tying shoelaces (Banich, 1998; Brown & Jernigan, 2012).

The brain develops in response to experiences that are unique to each individual, such as playing with specific toys or participating in social interactions.

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