The Bilingual Advantage

"If you have two languages and you use them regularly, the way the brain’s networks work is that every time you speak, both languages pop up and the executive control system has to sort through everything and attend to what’s relevant in the moment. Therefore the bilinguals use that system more, and it’s that regular use that makes that system more efficient. "

http://www.nytimes.com/2011/05/31/science/31conversation.html