Most neurons in the human brain last a lifetime, and for good reason. Intricate, long-term information is preserved in the complex structural relationships between their synapses. To lose the neurons would be to lose that critical information — that is, to forget.
Intriguingly, some new neurons are still produced in the adult brain by a population of cells called neural stem cells. As brains age, however, they become less and less adept at making these new neurons, a trend that can have devastating neurological consequences, not just for memory, but also for degenerative brain diseases such as Alzheimer’s and Parkinson’s and for recovery from stroke or other brain injury.