A comparison of magnetic and electrical stimulation of facial nerve at the cerebello-pontine angle in the dog.

Magnetic stimulation is a painless, non-invasive technique which allows an alternative method for testing cranial nerves which were previously inaccessible. We compared the latency of muscle responses obtained by electrical stimulation of the facial nerve at the cerebello-pontine angle (CPA) to high intensity transcranial magnetic stimulation (TMS) in 6 dogs. Evoked muscle response from the levator nasolabialis during electrical stimulation had a mean latency of 6.24 +/- 0.42 msec, compared with a mean of latency of 6.13 +/- 0.50 msec obtained by magnetic stimulation. Orbicularis oculi had a mean latency of 3.65 +/- 0.34 msec compared with a mean latency of 3.53 +/- 0.36 msec for magnetic stimulation. This suggests that high intensity TMS results in direct activation of the facial nerve as it exits the brain-stem in dogs. This observation is in accord with previous clinical studies that magnetic stimulation results in activation of the intracranial segment of the facial nerve in man.