I really cant say if I simply feel that way, or if there is an scientific background to it, but thinking non-fictional feels to happen in the area of my brain that is halfway between eyes and ears, from the spot behind the skullbone until an inch deep in the skull.
Thinking about fictional stuff likes book triggers me more far behind, so more of an area behind my ears, but not directly behind the skull, but more in the middle.
And the way that stuff feels for me, is like a very, very soft sense of tiggling. So as if you were medically numbed, so that you almost cant feel anything, and got poprocks on your tongue, that you only mention very damped.