Transcranial magnetic stimulation (TMS) applied to the motor cortex can inhibit upper motor neurons, preventing voluntary movement.

“It was placed over my motor cortex, which generates voluntary action and it was a coil that at that time could only inhibit neurons and so what I was doing as I was moving objects around on a table, just like I am now, it was actually a pencil, not a pen and I was tapping the pencil and then the TMS coil was turned on and for the life of me, I could not move that pencil, okay? Because it was inhibiting my upper motor neurons in the portion of my cortex that controls voluntary activity.”