The brain develops in a predictable sequence, from the most basic functions to the most complex ones. The interaction of genetic inheritance and environment determines how the brain will develop.
There are five basic processes that make up brain development. Many of these processes begin before birth, during the prenatal period. Most are not complete until late adolescence.
- Neurogenesis is the process of forming neurons. This is the first process to occur in brain development, and is completed before a baby is born.
- Neural migration is the process of organizing the brain by moving neurons to specific areas based on the functions these cells will perform. Migration begins prenatally, but continues for at least 8 to 10 months after a baby is born.
- Myelination is the process of coating the axon of each neuron with a fatty coating called myelin, which protects the neuron and helps it conduct signals more efficiently. Myelination begins in the brain stem and cerebellum before birth, but is not completed in the frontal cortex until late in adolescence. Breast feeding contributes to more rapid myelination in the brain.
- Synaptogenesis is the process of forming networks of connections in the brain. Synapses begin forming prenatally, but the process continues throughout life.
- Pruning is the process of weeding out unnecessary connections and strengthening the important ones, based on the child’s experiences. Some pruning begins very early in development, but the most rapid pruning happens between about age 3 and age 16. Different areas of the brain undergo pruning during different sensitive periods.
Pruning is a process that is more important than was once believed. Experiences during infancy and childhood form the connections that shape the development of the brain. Pruning is a key part of brain development because it eliminates the connections that are not used often enough. Pruning provides room for the most important networks of connections to grow and expand, making the brain more efficient.