Simon Calder meets people who keep learning new languages not because they have to, but because they want to. What motivates them? Situations like this - an immigrant hotel cleaner who is moved to tears because you speak to her in her native Albanian; A Nepalese Sherpa family that rolls about laughing in disbelief at hearing their foreign guest speak Sherpa. But do polyglots have a different brain from the rest of us? Simon travels to a specialised lab at the Massachusetts Institute of Technology, and undergoes a brain-scan himself, to find out.