Most of the brain’s cells are formed before birth, but the weight of a newborn’s brain is about 25% of its approximate adult weight. For a few years after birth the brain continues to grow through glia dividing and multiplying; these are the non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for neurons in the brain. By the age of 2 years, the brain is about 80% of the adult size (Dekaban & Sadowsky, 1978). The neurons in the brain make many new connections after birth, but most of the connections among cells are made during infancy and early childhood, as responses to new experiences and learning, which continue throughout life but occur most intensively during early childhood, especially in the first three years of life. By the age of 20-25 years the brain has matured, but some developmental processes, such as axon myelinization, extend into adulthood and continue until 40 years of age (Sowell, Thompson, & Toga, 2004). Then after middle adult age, multiple aging-related changes occur in the brain, which are clearly detectable by
