A study of the evoked electromyography of the superior orbicularis oris muscle in man

A study was made of the impulse conduction speed by moving recording electrodes at 5 mm intervals, successively, after stimulating facial nerves on one side in normal subjects. The findings showed that the speed of the potentials was fast and the amplitude was large, up to a distance of 0.5 cm across the midline. This makes us believe that there is an intermingling, of approximately one cm, of the left and right superior orbicularis oris muscles. Evoked potentials were recorded up to 1.5 to 2.5 cm across the midline--but as the speed reduced abruptly and the amplitude became small, we believe these potentials were conveyed by volume conductors. Six patients with facial palsy were studied, but in none were these findings indicating any reinnervation from the normal side. However, the conduction speed was delayed in them (as compared to normal subjects).