Part of the Brain: The Inside Story exhibition.

Of all the organs in your body, the brain takes longest to mature. It grows dramatically when you are very young and continues to develop at a slower pace until you become an adult. What changes take place in the brain as you grow up?

How it Works

Before Birth

Before a child comes into the world, the brain grows very rapidly. On average, 500,000 neurons form every minute during the first five months in the womb. These neurons soon specialize, move to their proper positions, and form the connections needed for sensing, moving, and thinking. Not long before birth, layers of a fatty material called myelin start forming around the axons. Like coating on an electric wire, myelin acts as a kind of insulation, helping electrical signals travel faster from neuron to neuron. By the time a baby is a few months old, almost all the neurons are in place, but millions of new connections will continue to form.


During childhood, neurons grow by sprouting branches called dendrites, making more connections than the brain will ever need. As a child grows up, connections that are used often are reinforced, while others are stripped away. This process, known as pruning, helps control the flow of signals so the brain works smoothly and efficiently. A child's brain is still taking shape, so it is especially flexible. Motor skills and abstract thinking develop steadily during this time.


By the teenage years, the only unfinished part of the brain is the outer layer, the cortex. Neural connections multiply in the prefrontal cortex until age 11 or 12. In the teenage brain, this area thins out as unused connections are pruned away and more active connections are strengthened. A teenager's brain is supple and open to change, and skills learned at this age are likely to last a lifetime. And risky habits picked up during the teenage years, such as alcohol and drug abuse, are especially hard to shake.