Yesterday I mentioned the syndrome of "Heifetz Face" - the directing of energy into the music rather than into emoting or histrionics. It doesn't mean the performer demonstrates nothing at all of his/her ongoing musical response, just that he/she keeps it to a minimum and the music speaks for itself - often rather well. Here are a few examples of it.
Heifetz himself, of course:
And here is the opposite.
Lots of different ways of doing things, of course. It's all part of life's rich tapestry.