There was an old study showing that London taxi drivers develop enlarged hippocampi, the part of the brain used for navigation, to deal with the labyrinthian London streets. The growth continued over several years even in mature adults as they used those navigation and memorization abilities. I’d like to see a study of the brain of an adult prospective language learner over a long period to see if any similar plasticity exists for the brain’s language centers.

(I’ll admit I’m horribly biased. I was exceptional at picking up new languages as a teen, but let that knowledge decay into nothingness as an adult. I’d hate to have wasted such a useful talent.)