Fascinating Australian Broadcasting Co science piece on the latest research in neuron production:
we do know a couple of things that stimulate brain cell production. One of them, of course is anti-depressants, which we now know probably the key molecule by which this acts, because we've been able to purify these cells that make neurons and we know what are the receptors that bind molecules. And one of these receptors turn out to be a receptor for a neurotrophine, a molecule that keeps nerve cells alive traditionally. But we know that anti-depressants raise the molecule that binds to this receptor and we now know that this is the factor that can stimulate the production of new nerve cells. So we think we've made the connection between anti-depressants and production of new nerve cells. But there are many other ways of stimulating the production and some of them are pretty damned interesting. One is if you put an animal on a wheel and let it run ad libitum and they run up to about 10 kilometres overnight, they make about twice as many neurones.
The other thing is that certain molecules produced during sex also appear to be highly stimulatory of neuronal production. Prolactin levels, which pregnant women have enormous amounts of, also stimulate large amounts (of neurons).
(Thanks, Adrian!)