Antidromically evoked facial nerve responses in guinea pigs: a basis for clinical applications in patients with facial palsy

Summary

We investigated the differences in wave form in antidromically evoked facial nerve responses in guinea pigs with and without facial nerve dysfunction. The antidromic facial nerve responses were evoked with alternative stimulation of positive and negative square-wave pulses of 0.1 ms duration and recorded at the bony fallopian canal near the geniculate ganglion. One hundred responses were summed by a signal processor. The application of alternative stimulations made it possible to eliminate stimulus artifacts and to analyze precisely the waves with latencies shorter than 0.5 ms in the test animals. Normal antidromic facial nerve responses showed a triphasic wave form with two positive and one negative peaks. A blockade of the nerve between the recording and stimulating sites resulted in transformation of the wave into a monophasic one. A proximal blockade to the recording site changed the wave form to a biphasic shape. These findings suggest that the site of an intratemporal facial nerve lesion can be predicted from the wave forms evoked by antidromic facial nerve responses.