Читать книгу Infants and Children in Context - Tara L. Kuther - Страница 214

The wrinkled and folded outermost layer of the brain is known as the cortex. The cortex comprises about 85% of the brain’s mass and develops throughout childhood and some parts mature into early adulthood.

The cortex is composed of different structures with differing functions, located across four lobes. The various parts of the brain work together; however, as shown in Figure 4.9, each lobe is specialized to a certain extent. The four lobes progress on different developmental timetables. The sensory and motor areas tend to develop first (for example, the visual cortex regions of the occipital lobe). The frontal lobe, specifically a part called the prefrontal cortex, develops throughout infancy, childhood, and adolescence, maturing into early adulthood (Hodel, 2018; Tamnes et al., 2017). The prefrontal cortex is the part of the brain responsible for higher thought, such as planning, goal setting, controlling impulses, and using cognitive skills and memory to solve problems.

In addition, the cortex is composed of 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. Over childhood, the right and left hemispheres become specialized to carry out different functions, a process known as lateralization (Duboc, Dufourcq, Blader, & Roussigné, 2015). 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.

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Figure 4.9 The Human Brain

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 over the course of childhood, 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).