Probably only one. There are times when it feels like two are more are going on at the same time, but I think it comes down to another thought quickly creeping in and taking over the lead role. For example, when driving on a familiar road, thoughts stray, and then I suddenly look up and have to refocus on where I am. It isn’t a matter of turning off the thought process of driving safely to the destination; one thought just takes a front seat for a moment. (Is this what you mean?)