Though not entirely surprising, still useful confirmation from William Alexander of the benefits of learning a new language, particularly for adults:
All this means that we adults have to work our brains hard to learn a second language. But that may be all the more reason to try, for my failed French quest yielded an unexpected benefit. After a year of struggling with the language, I retook the cognitive assessment, and the results shocked me. My scores had skyrocketed, placing me above average in seven of 10 categories, and average in the other three. My verbal memory score leapt from the bottom half to the 88th — the 88th! — percentile and my visual memory test shot from the bottom 5th percentile to the 50th. Studying a language had been like drinking from a mental fountain of youth.
Read more here of "The Benefits of Failing French."