You've just posted on a favorite subject of mine.
I've never hunted down any scholarly articles in particular, but over the years I've definitely noticed them here and there - articles that make the connection between the 'play' brainstate and learning.
I would go so far as to say only a few ways of 'learning' actually exist, and different types of learning. 'Play' seems the best for innovation and discovery (one kind of learning). Adrenylated experiences (fear, excitement, anger, intense love) seem the best ways of encouraging or discouraging behaviors.
My favorite: combining adrenylated experiences with play-states creates the most whacked out intense learning.
Martial-artists who lose the sense of 'play' but acquire an adrenylated-state during drills and sparring quickly start sucking. However, to have drilled in a 'play' state means that when confronted with the 'real' scenario, with its rush of adrenyline, one tends to learn some really intense things that one never forgets, and survive to retain it.
Play does not mean 'goofing off', although it can involve 'goofing-off'.
I own all this as my own perspectives on play and learning - I don't know that it appears in this form in any scientific article.
We've just started having role-playing game days to drill story-telling skills (if you haven't read my blog). I see these having a huge potential.
In any case, the old paradigm of "exercises" that "teach" you things sucks, I think. Either play games, or do the real thing, but no more 'exercises', I say.