Observe Abnormal Potential From the Offending Vessel to the Facial Muscles of HFS Patients

It's hypothesized that at the location where the facial nerve is compressed by an artery, ephaptic cross-transmission takes place between the nude facial nerve fibers and the sympathetic nerve fibers on the arterial surface. Thus action potentials could spread indirectly from one facial nerve fiber to several other facial nerve fibers (via the "bridge" of sympathetic fibers), or directly from the sympathetic fibers to facial nerve fibers. The investigators assume this is the electrophysiological basis of hemifacial spasm and its characteristic sign abnormal muscle response (AMR). If an abnormal potential from the offending artery to the facial muscles similar to AMR can be recorded, the hypothesis will be verified.