Possible explanations for talented language learning fall into two general areas. One view says: What matters is a person's sense of mission and dedication to language learning. You don't need to describe high performers as biologically exceptional, because what they do is a product of practice. Anyone can become a foreign-language expert - even an adult. (...) The other view says: Something neurological is going on. We may not know exactly what the mechanisms are, but we can't explain exceptional outcomes fully through training or motivation.

Babel No More: The Search for the World's Most Extraordinary Language Learners