Harvard University: Brain Architecture

Brains are built over time, from the bottom up. The basic architecture of the brain is constructed through an ongoing process that begins before birth and continues into adulthood. Simpler neural connections and skills form first, followed by more complex circuits and skills. In the first few years of life, more than 1 million new neural connections form every second.* After this period of rapid proliferation, connections are reduced through a process called pruning, which allows brain circuits to become more efficient.