Waveform morphology and amplitude variability in facial-nerve electroneurography

This study assesses the effect of using bipolar recording electrodes in the nasolabial crease versus using monopolar recording electrodes in the crease and on the nasal alae. Seven normal patients had three trials of facial-nerve electroneurography on three separate test days. Peak-to-peak amplitudes of combined motor action potentials were measured; amplitude variability was not affected by the measurement site. A biphasic waveform shape was most consistently obtained by using the nasal alae as the recording point rather than the nasolabial crease. We hypothesize that alar electrodes primarily detect combined motor action potential activity from relatively synchronous, fast-conducting facial-nerve fibers, while the combined motor action potential detected by electrodes in the nasolabial crease reflect a relatively complex summation of both fast and slow fibers.