http://www.cal.org/earlylang/benefits/marcos.html

https://www.researchgate.net/profile/Gregory_Yelland/publication/231845167_The_metalinguistic_benefits_of_limited_contact_with_a_second_language/links/54bd88ce0cf218da9391b381.pdf

http://bebrainfit.com/brain-benefits-learning-second-language/

http://www.medicaldaily.com/bilingual-benefits-how-learning-another-language-keeps-your-mind-sharp-no-matter-your-310308