It’s not external muscle control, that’s not what a TENS unit does. OP is describing using painful electric shocks to punish a worker for mistakes or for going off-task, i.e. brutalize workers into performing with machine like efficiency.
You still can't just "turn off" your mind, most likely. You'll just be trapped there thinking
It's pretty astonishing how much variation there is in people's inner minds. Some can imagine spatial relationships in great detail. Some can't even imagine a simple stick figure, but can instead remember long lists of information.