Now let's explain. Almost any excercise or dance is a wonderful hobby to pursue well into old age. However, for intellectual benefits, only those which require quick critical thinking have the power to boost our intellectual clarity as well. Quite simply, if our muscle memory has been doing the same thing for years, and we could practically perform on auto-pilot, our brain is not making any new connections - it just follows an old path that is well ingrained. When we do any kind of improvisational dance, our brain constantly has to make snap decisions, and this is what keeps us sharp.
When leading in ATS, we are making many decisions about which move to perform next, based on the music, mood, ability of dancers around us, and probably other factors I'm missing. When we follow it may seem we're in much a more passive role, but in fact we are constantly reading the body language and cues of our leader. Of course we know as well that often the leader hat changes quickly - during turns, fading, etc. All of this quick decision making is what makes improvisational dance stand out from the others in this aspect of health. Not that we needed another reason to keep dancing! ;)
Richard Powers 'Use It or Lose It: Dancing Makes You Smarter'
His website: http://richardpowers.com/