Lol, scanning player's brains... That just sounds so wrong.
Even though it's a very logical thing to do, especially from a money-making perspective. If you want to make games people enjoy/etc., you'd want to see how they react to certain things instead of just guessing.
Same how they measure your heart rate/etc. when testing a new energy drink, right? They don't just release it and see how well it sells, and then adjust.
Btw, brain scanning for purposes of finding out more about (abnormal) patterns of sleep is a very common and acceptable practice. Nothing wrong with that.
But when you say you'll be doing it for games, that just kinda sounds a little off.