Apologies in advance because I am having trouble finding the citation.
Edit: based on some searching, it appears that mental exercise does enhance neurological function among seniors. However, aerobic exercise has an equal or greater impact. I suspect combining both would be the best.
http://www.sciencedaily.com/releases/2001/01/010117074808.ht...
http://www.emaxhealth.com/36/21947.html which references http://www.ncbi.nlm.nih.gov/pubmed/9346168
Here's a reference to a Columbia study: http://www.nytimes.com/2007/08/19/sports/playmagazine/0819pl...
However I'm failing to find the study comparing mental games and aerobic exercise among seniors.
Now, what you are describing may be a case of self-selection. It may be possible (though I do not concede this point) that smarter people tend to gravitate toward the more oddball sports. That doesn't indicate that sprinting does not benefit the brain. Here's a thought experiment:
There are 100 people at the pool and 50 life jackets. People are allowed to choose to use a jacket or not, until all jackets are gone. You may find that better swimmers on average choose not to use a jacket. That does not indicate that the life jacket is not useful for swimming.
Re: the lifejackets I was demonstrating that the effectiveness of the jackets is not effected by who chooses to use them. I was pointing out that saying less intelligent people gravitate towards sprinting does not prove that sprinting has no positive benefits on intelligence.
Oh, perhaps that was pedantry?
"Nerve conduction velocity (NCV) has been shown to increase in response to a period of sprint training." http://www.ingentaconnect.com/content/adis/smd/2001/00000031...
When you sprint, your brain must fire every signal, and process every step so you can keep your balance. Sprinting is, by definition, running as fast as you can, which also means running as fast as your brain can process it. By training it, you train your brain to think at a higher speed than it normally would.
The cited study postulates in the discussion that Tip of Tongue events come from simple reduced frequency of use in any given word stemming from a much larger lexicon. There's no evidence at all suggest that there's actually a neurological disadvantage to bilingualism.
Also, it seems pretty counterintuitive to think that practice in an entirely new cognitive arena, something like a new language, could do anything but improve your ability to process language. If there's a paper out there I'd love to read it.
That hardly makes it the only one that matters. I personally have derived enormous benefits from studying Latin. There have been several times I have wished I spoke Spanish and a few times I had wished I could speak Japanese, Pashtun, Arabic, and Dari.
Knowing more languages is definitely a good thing.
Knowing multiple languages is extremely valuable.