Nide--It's a myth that the cns does not grow new nerve cells. Whether "old" ones are regenerating, I don't know, but I do know, for sure, that the brain grows new cells, and that the thing we learned from Christopher Reeves, was that the spinal cord was capable of healing itself in ways we never thought. For instance, in the brain, the antidepressants, the SSRIs, likely work by causing new growth, especially in the hippocampus. It is likely that the way they relieve depression has NOTHING to do with their effect on serotonin, but rather their effect as a nerve growth factor.

I'm sure much more will be learned about this in the future, especially with research relating to our war veterans. The thing that's clear, however, is that if you don't stimulate nerves, they don't regenerate, so even for damaged nerves, the rule is, use it or lose it.