It has been discovered that neurogenesis takes place only on the hippocampus.
Quoting Leonard E. White:
We now agree that the production of new
neurons in the human brain is really
limited to a special set of stem cells
that seem to sit in the basal region of
dentate gyrus of the hippocampus.
So in this subgranular zone, we have a
population of neural stem cells that can
differentiate into interneurons that are
found in the granule cell layer of the
hippocampus.
Also as you said, this production could be modulated through some interventions (e.g. learning)
This genesis of new
neurons in the hippocampus can be
modulated.
By all kinds of different interventions
including pharmacological agents such as
antidepressant medications.
As well as physical interventions, such
as exercise.
Also, this has been mentioned in this ted talk:
https://www.ted.com/talks/sandrine_thuret_you_can_grow_new_brain_cells_here_s_how
In summary, the following activities impact positively on neurogenesis:
- Learning
- Sex
- Running
- Good diet
While these ones impact negatively:
pd: Concerning how memory works, my knowledge there is limited.