If it helps, I'm reasonably sure it's the soft palate muscles. To cause the effect you're describing, I visualize tensing a muscle that runs directly from one e

If it helps, I'm reasonably sure it's the soft palate muscles. To cause the effect you're describing, I visualize tensing a muscle that runs directly from one ear to the other, through the middle of my skull. It's one of those things where trying to describe it to someone who physically can't do it or doesn't know how to may make them question your judgment and/or sanity.