Although most of the cells in the human body renew themselves periodically, the majority of the neurons in the brain are produced before birth in a process called neurogenesis, and serve humans for their entire lives. Some portions of the brain, however, add new cells during infancy, and one part in particular, the hippocampus, adds cells throughout an individual's lifetime.
There are approximately 100 billion neurons in the human brain and spinal column, and most of these are already in place by the time humans are born. However, shortly after birth, a number of new cells are added to several areas of the brain, including the cerebellum, the olfactory bulb, the prefrontal cortex and the hippocampus. Except for the hippocampus, an area of the brain dedicated to learning and memory, any new production of cells ceases at around age 2.