Facial Nerve Antidromic Evoked Potentials
Recording facial nerve potentials generally involves peripheral stimulation of the extratemporal facial nerve and recording a combined electrical potential representing: (1) the peripheral facial muscular response (EMG) and (2) a small proximal antidromic response. In most cases, the very small antidromic facial nerve potential cannot be differentiated from the much larger EMG muscular response. The antidromic response occurs from a progressive depolarization along the intratemporal portion of the nerve into the facial motor nucleus. The spatial orientation of the motor cells within the facial nerve nucleus may account for some of the difficulty in recording this potential. Antidromic responses of the facial nerve are affected by pathologic injury to the facial nerve, i.e., nerve compression. Experimental results in animals with recording of the antidromic evoked potential along the facial nerve and within the facial nerve nucleus are presented. Suggestions for improved recordings in humans are discussed.