While the vast majority of the brain's cells are formed during prenatal development, there are certain areas of the brain that continue to create new neural cells - a process known as neurogenesis - during infancy. Perhaps even more surprising, there is at least one important area of the brain that continues to create new cells throughout the entire lifespan.

During the 1990s, researchers conducted studies that involved injecting participants with a compound that is taken up into a cell's DNA. The researchers discovered that the hippocampus - a region of the brain associated with memories, learning, and emotions - continues to create new cells well into old age. Today, scientists understand that adult neurogenesis is not only possible, it is a regular occurrence.

Later studies that involved looking at how nuclear fallout impacted human cells allowed researchers to further demonstrate that the human hippocampus generates new cells. Cells in the hippocampus are also continually dying. The formation of new nerve cells allows the hippocampus to maintain a balance, although the number of cells usually does begin to decline with age.

Why is the formation of new brain cells such important news? Researchers believe that it raises the possibility of treating degenerative brain diseases including Alzheimer's and Parkinson's. It may also mean that one day scientists can develop new treatments for brain trauma and injury.

While there have been indications that the brain grows new cells for decades, it wasn't until recently that research has confirmed these suspicions. Why did the idea that the brain was largely set in stone after birth persist for so long? Partly because many experts believed that in order to form lasting memories and store information over a long period of time, it was essential that the brain be relatively stable.