Jun's article references are good. Greg Olson has done about the only research on this topic. The nerves are primarily the superficial branch of the radial nerve. You can feel this on some people by stroking a firm object down the radial bone on the thumb side. Some people with feel a tingling when this is done. Apparently, the other nerve is the median depending on which version of the technique is being performed.
Another possibility is pain over the bone due to pressure on the periosteum (outer layer of the bone).