What evidence is there that the adult brain can produce new neurons? At school I was taught that the adult brain did not produce new neurons. That we had the maximum number of neurons and this would only diminish over time due to events, like head injuries, drinking excessive quantities of alcohol, various other processes, not to mention the general atrophy the body experiences through the process of aging.

I remember sitting through a Neuroscience lecture (about 15 years ago), and learning, that studies had shown that whilst exercising enabled the brain to produce new neurons.

What is the latest evidence that the adult brain can produce new neurons?



Please note the link is not to the lecture I refer to.
For a comprehensive review, see:

Berg, D.A., Belnoue, L.,Song,H., Simon A. (2013) Neurotransmitter-mediated control of neurogenesis in the adult vertebrate brain.  Development, 140(12), 2548-2561. [DOI].

Briefly,


  active adult neurogenesis is confined to two distinct
  locations: the subventricular zone (SVZ) of the lateral ventricles in
  the forebrain; and the subgranular zone (SGZ) of the dentate gyrus
  (DG) in the hippocampus


These areas contain radial glial-like cells, which act as neural stem cells, and the growth of which is modulated by the respective neurotransmitters.  For example, cells which are GABAnergic will be modulated (enhanced in the SVZ and inhibited in the DG) via GABA that has diffused out of the synapses of neighboring cells


  GABA is released from parvalbumin-expressing interneurons in the adult dentate gyrus
  (DG) and inhibits the activation of quiescent RGLs through activation of the γ 2-subunit-containing GABA A
  receptor.
  
  In the SVZ, GABA also signals to and depolarizes neural
  progenitor cells, but the mechanism of release is different from that
  in the DG (Wang et al., 2003; Liu et al., 2005). Migrating
  neuroblasts release GABA in a non-synaptic, non-vesicular fashion,
  which tonically activates signaling in progenitor cells.  


There are mechanisms through which the progenitor cells are stimulated that rely on neurotransmitters, but are not specific to cell subtype:


  Neurotransmitters control neurogenesis without subtype specificity. If NSCs have restricted potential, transmitters could act on both NSCs and/or amplifying populations.


It's still a complicated story, but the long and short of it is, in specific regions of the brain, adult neurogenesis is known to be possible and some of the neurotransmitter-based growth factors are now being elucidated.