UNKNOWN.
HGH, IGF, all those guys might help. basically, when your body produces these, they also produce NGF - nerve growth factor. it MAY work like testosterone, where if you get an incoming supplement that replaces it, your body produces something different - estrogen. IF, and i say IF, because there is no documentation, proof, or studies, you were to take HGH or IGF, you MAY increase your production of NGF, which would be the targeted hormone.
better to just go through a bio company and get some NGF, since anything else is speculation.
I would tend to believe high amounts of HGH would lead to a higher output in NGF though. look at neurotomy surgery, where you zap and kill the nerve. this procedure has to be done every 7 months to 5 years - depending on..... what is that "depending on", and why would someone recover from that almost 10 times faster than someone else? has to be a hormonal difference - though for all i know, its a naturally high output of NGF. again, pure speculation. harvard did a study on NGF and restoring nerves in 2006 in a pietrie (sp?) dish. as far as i know, no human studies have been done, though i don't really keep up on this.