Damaged human brain cells do not regenerate because the process that creates brain cells, neurogenesis, ceases before birth for many brain structures and in all but one brain structure by age two, according to BrainFacts.org. Brain cells only regenerate in the hippocampus.
The hippocampus is a brain structure that is heavily involved in learning and memory, BrainFacts.org notes. It's the only brain structure that regenerates cells throughout life. The cerebellum, olfactory bulb and prefrontal cortex all continue to grow new brain cells until age two. All other brain structures cannot regenerate cells after birth.
The human brain and spinal cord contain approximately 100 billion nerve cells. They are the only cells in the human body that do not regenerate. For example, human skin, liver and heart cells regenerate at a high rate. Other animals, such as fish, amphibians and birds, have a high turnover rate of brain cells. Turnover of brain cells in mammals is more limited than other animal groups. For example, only two regions of rodent brains continue to acquire new cells throughout life. Humans are the only mammal known to have regeneration in just one brain structure. BrainFacts.org theorizes that the inability to regenerate brain cells may make human brains more stable and allow for longer-term memory.