Читать книгу Lifespan Development - Tara L. Kuther - Страница 350

Early childhood is a period of rapid brain growth. The increase in synapses and connections among brain regions helps the brain to reach 90% of its adult weight by age 5 (Dubois et al., 2013). In early childhood, the greatest increases in cortical surface area are in the frontal and temporal cortex, which play a role in thinking, memory, language, and planning (Gilmore, Knickmeyer, & Gao, 2018). Children’s brains tend to grow in spurts, with very rapid periods of growth followed by little growth or even reductions in volume with synaptic pruning (see Chapter 4) (Jernigan & Stiles, 2017). Little-used synapses are pruned in response to experience, an important part of neurological development that leads to more efficient thought.

The natural forming and pruning of synapses enables the human brain to demonstrate plasticity, the ability of the brain to change its organization and function in response to experience (Stiles, 2017). Young children who were given training in music demonstrated structural brain changes over a period of 15 months that correspond with increases in music and auditory skills (Hyde et al., 2009). Plasticity enables the young child’s brain to reorganize itself in response to injury in ways that the adult’s brain cannot. Adults who suffered brain injuries during infancy or early childhood often have fewer cognitive difficulties than do adults who were injured later in life.

Yet the immature young brain, while offering opportunities for plasticity, is also uniquely sensitive to injury. If a part of the brain is damaged at a critical point in development, functions linked to that region will be irreversibly impaired. Generally speaking, plasticity is greatest when neurons are forming many synapses, and it declines with pruning (Stiles, 2017). However, brain injuries sustained before age 2 and, in some cases, 3 can result in more global, severe, and long-lasting deficits than do those sustained later in childhood (V. A. Anderson et al., 2014), suggesting that a reserve of neurons is needed for the brain to show plasticity. Overall, the degree to which individuals recover from an injury depends on the injury, its nature and severity, age, experiences after the injury, and contextual factors supporting recovery, such as interventions (Bryck & Fisher, 2012).

Lateralization, the process of the hemispheres becoming specialized to carry out different functions, continues through early childhood and is associated with children’s development (Duboc, Dufourcq, Blader, & Roussigné, 2015). For example, language tends to be lateralized to the left hemisphere in adults, and lateralization predicts children’s language skills. Young children who show better performance on language tasks use more pathways in the left hemisphere and fewer in the right than those who are less skilled in language tasks (M. Walton, Dewey, & Lebel, 2018).

Myelination contributes to many of the changes that we see in children’s capacities. As the neuron’s axons become coated with fatty myelin, children’s thinking becomes faster, more coordinated, and complex. Myelination aids quick, complex communication between neurons and makes coordinated behaviors possible (Chevalier et al., 2015). Patterns of myelination correspond with the onset and refinement of cognitive functions and behaviors (Dean et al., 2014). Myelination proceeds most rapidly from birth to age 4, first in the sensory and motor cortex, and then spreads to other cortical areas through childhood into adolescence and early adulthood (Qiu, Mori, & Miller, 2015).