To observe neuron generation we label a scattering of cells inside the developing nervous system. We do this in the chicken embryo, which is easily accessible inside the egg. We study this in the forming spinal cord, as this is simplest region of the neural tube. Cells divide to expand the pool of neural progenitors and some of these cells then stop dividing and differentiate into neurons. We follow the first neurons to be born. These are the easiest to see and they become the scaffold upon which later-born neurons navigate to their targets
New neurons are also generated in adult brains. A key site for this is a region called the hippocampus, which is involved in memory and learning. There is growing evidence that adult neurogenesis is required for memory and learning.
Reviews of recent research:
C. Anacker, R. Hen ( 2017) Adult hippocampal neurogenesis and cognitive flexibility - linking memory and mood. Nat. Rev. Neurosci. 18, 335–346.
S. Yun, R. P. Reynolds, I. Masiulis, A. J. Eisch, Re-evaluating the link between neuropsychiatric disorders and dysregulated adult neurogenesis Nat. Med. 22, 1239–1247.
J. T. Gonçalves, S. T. Schafer, F. H. Gage, ( 2016) Adult Neurogenesis in the Hippocampus: From Stem Cells to Behavior. Cell 167, 897–914
Recent advance uncovering patterns of proliferation in adult mouse hippocampus and integration of new born neurons into neuronal circuits.
Pilz GA, Bottes S, Betizeau M, Jörg DJ, Carta S, Simons BD, Helmchen F, Jessberger S (2018) Live imaging of neurogenesis in the adult mouse hippocampus Science. 2018 Feb 9;359(6376):658-662
There is also some controversy about the extent of neurogenesis in the adult human brain. This is an area of active research.
Some data suggest that this is not maintained in adult life:
Sorrells et al 2018 in the journal Nature
And other evidence indicates that it is:
Boldrini et al 2018 in the journal Cell Stem Cell