Acoustic middle ear muscle reflex protection against magnetic coil impulse noise

Electromagnetic stimulation (EMS) of the brain and the intracranial portion of the facial nerve has become a widely used clinical technique. The high intensity impulse noise acoustic artifact generated by some magnetic coils used in EMS has been shown to cause severe cochlear damage in experimental animals. This damage results in permanent threshold shifts throughout the auditory spectrum of the rabbit. As with other impulse and impact noise signals, the duration of the coil impulse noise is too short to be influenced by the normally protective acoustic middle ear muscle reflex. Artificially activating the acoustic reflex with a contralateral broad band noise during exposure to the intense coil artifact reduced the compound threshold shift (CTS) significantly, and the permanent threshold shifts (PTS) to near zero at each tone frequency and noise band tested. The results demonstrate the effectiveness of a suprathreshold sound in activating the acoustic middle ear muscle reflex and protecting against impulse noise-induced hearing loss caused by high frequency magnetic coil acoustic impulses.