There was a pretty decent bit about brain health on last week's edition of Science Friday. The NPR website is not the easiest thing to navigate, so you can use the toolbar below to hear the podcast version.
I'm acquainted with a few people who study the effect of exercise on the brain, though I'm not up on the research myself. As far as I can tell, this is an accurate summary of the field. At the very least, it debunks a lot of the pop psychology associated with maintaining a healthy brain.