I'm not quite sure exactly what I'm doing; it feels a bit like tensing a muscle, but that muscle feels like it's in the middle of my head, a bit toward the back. Obviously there are no actual muscles there, so I'm not sure what's actually happening.
If you try raising one eyebrow or wiggling one ear (assuming you can't already do that), you might find that you're briefly activating lots of little muscles around the target as your body tries to figure out where that's mapped in your brain. Once you get the right muscle, you can relax the other false positives, and eventually just have the single muscle isolated. It's similar in my "brain flow" thing: usually a couple random muscles in my head want to join in, but I can intentionally relax them and keep the "flow" going. A common one is the tensor tympani -- the two "muscles" seem to be closely mapped together. If you can rumble your ears (manually activating the tensor tympani), try initiating a rumble, and then "move" the activation in between your ears, right to your mid-back brain. (Again: I know there's no actual muscle there, so /shrug).
I sorta get what you're saying, and tbh I've always found it hard to single out a single muscle from all the other tiny muscles around it. I can already raise one eyebrow alone, and I don't remember when I learned to do it so I don't remember the experience, but I do feel that 'single muscle vs many muscles' when I do that.
With the "muscle" in the mid-back of your brain, I understand that much more. If you respond well to meditation and get a sensation from asmr for instance, if we're speaking on the same area, that area gets sensations if the person is more prone to stress.
When I sort of make myself hotheaded, or have any drug, or even really relax, I feel sensations at that area. I wonder if you're the same.
If you try raising one eyebrow or wiggling one ear (assuming you can't already do that), you might find that you're briefly activating lots of little muscles around the target as your body tries to figure out where that's mapped in your brain. Once you get the right muscle, you can relax the other false positives, and eventually just have the single muscle isolated. It's similar in my "brain flow" thing: usually a couple random muscles in my head want to join in, but I can intentionally relax them and keep the "flow" going. A common one is the tensor tympani -- the two "muscles" seem to be closely mapped together. If you can rumble your ears (manually activating the tensor tympani), try initiating a rumble, and then "move" the activation in between your ears, right to your mid-back brain. (Again: I know there's no actual muscle there, so /shrug).