No Answers - Is This Unknown? "What Causes New Neurons to Form?"

Last week I asked “What Causes New Neurons to Form?”. There haven’t been any answers offered.

I’m having trouble finding any worthwhile publications on this topic. Given the above does that mean the answer is unknown?

What about synapses? I’m looking for any first principles on stimuli to generate new signal pathways: increasing synapse size/payload, increasing synapses to post-synaptic neighbor, new neuron generation.

Any information or guidance is extremely appreciated.

My previous post, for reference - What Causes New Neurons to Form?

Thank you