Those of us who run in part to stave off the slobbering advances of the Black Dog; there's a really interesting episode of All In The Mind on iplayer here bbc.co.uk/programmes/b08v09y4 - one of the researchers explains that 'neurogenisis' (growing new brain cells in the hippocampus) is inhibited in depressed brains, and that antidepressants only work when neurogenisis is happening. And guess what increases neurogenisis in rodents, by up to 50%? Running.
I'm extrapolating that information to decide that we're all getting bigger brains by getting out there π - but seriously, super interesting.