Plasticity

     The basic architecture of the brain is constructed through a process that begins early in life and continues into adulthood. Simpler circuits come first and more complex brain circuits build on them later. Genes provide the basic blueprint, but experiences influence how or whether genes are expressed. Together, they shape the quality of brain architecture and establish either a sturdy or a fragile foundation for all of the learning, health, and behavior that follow. Plasticity, or the ability for the brain to reorganize and adapt, is greatest in the first years of life and decreases with age.

   Some areas of the brain, such as those which help us see clearly, become less "plastic" or changeable when the pruning is over. This has led to tremendous concern about providing what the brain needs to prune and organize itself correctly before the "windows of opportunity" close. For example, surgeons now remove congenital cataracts as early in infancy as possible, because they know that if they wait until the child is older, the neural connections between his eyes and his brain will fail to develop properly, and he will never be able to see.

   Our brains shape and reshape themselves in ways that depend on what we use them for throughout our lives. Learning language is an example of how experiences contribute to each person’s unique pattern of brain development.  However, which language a child learns to speak depends on the language he experiences, and his brain will adapt to this specific language. When an infant is 3 months old, his brain can distinguish several hundred different spoken sounds, many more than are present in his native language. Over the next several months, however, his brain will organize itself more efficiently so that it only recognizes those spoken sounds that are part of the language that he regularly hears. After about age 10, however, plasticity for this function is greatly diminished; therefore, most people find it difficult to learn to speak a foreign language as well as a native speaker if they only begin to learn it in adolescence or adulthood. Early experiences can determine how proficient a child becomes in his or her native language. Researchers found that when mothers frequently spoke to their infants, their children learned almost 300 more words by age 2 than did their peers whose mothers rarely spoke to them.