Neurogenesis appears to play a role in both remembering and forgetting.

Neural stem cells have the potential to generate all neural cell types. They differentiate into neuronal progenitor cells, which give rise to neuron, or glial progenitors, which give rise to glial cells. (Image Credit: NCD Project / CC BY-SA 3.0 via Commons)

Neurogenesis is the process by which new neurons are formed in the brain. Neurogenesis is crucial when an embryo is developing but also continues in certain brain regions after birth and throughout our lifespan.   

The mature brain has many specialised areas of function, and neurons that differ in structure and connections. The hippocampus, for example, which is a brain region that plays an important role in memory and spatial navigation, alone has at least 27 different types of neurons.

The incredible diversity of neurons in the brain results from regulated neurogenesis during embryonic development. During the process, neural stem cells differentiate—that is, they become any one of a number of specialised cell types—at specific times and regions in the brain.

Researchers think neurogenesis helps the brain distinguish between two very similar objects or events, a phenomenon called pattern separation.

According to one hypothesis, new neurons’ excitability in response to novel objects diminishes the response of established neurons in the dentate gyrus to incoming stimuli, helping to create a separate circuit for the new, but similar, memory.

There are different types of neurons being born in the brain throughout life. The problem is their very small cells, they’re very scattered, and they're very few of them. So they’re very tough to see and very tough to study.

Do new neurons appear anywhere else in the brain?

"Many, though not all, neuroscientists agree that there’s ongoing neurogenesis in the hippocampus of most mammals, including humans. In rodents and many other animals, neurogenesis has also been observed in the olfactory bulbs.

Whether newly generated neurons show up anywhere else in the brain is more controversial.

There had been hints of new neurons showing up in the striatum of primates in the early 2000s. In 2005, Heather Cameron of the National Institute of Mental Health and colleagues corroborated those findings, showing evidence of newly made neurons in the rat neocortex, a region of the brain involved in spatial reasoning, language, movement, and cognition, and in the striatum, a region of the brain involved in planning movements and reacting to rewards, as well as self-control and flexible thinking (J Cell Biol, 168:415–27).

Nearly a decade later, using nuclear-bomb-test-derived carbon-14 isotopes to identify when nerve cells were born, Jonas Frisén of the Karolinska Institute in Stockholm and colleagues examined the brains of postmortem adult humans and confirmed that new neurons existed in the striatum."

https://www.ncbi.nlm.nih.gov/pubmed/24561062