Kocaeli University, School of Medicine, Department of Otolaryngology

Kocaeli, Turkey

Extracranial electromagnetic stimulation (EMS) is recently used in neurology and otolaryngology for non-invasive stimulation of the brain and facial nerve. We performed experimental trials designed to evaluate the utility of a unidirectional EM energy that pass through the otic capsule, on the auditory nerve stimulation. Therefore the purposes of this study were to determine the following: 1. The auditory sensation effects of various frequency, different flux density, and d_B/d_t waveforms of EM energy; 2. Whether the site and depth of a lateral cochlear wall electromagnetic inductor (EMI) affects the pattern of evoked responses; 3. The dynamic range of activation of the auditory pathway with extraluminal EMS; 4. Whether successful activation of the auditory nerve is possible without adventitial stimulation of the facial nerve; 5. The effects of long and short -term EMS on cytoarchitecture of the cochlea.

EMS of the auditory system was assessed in normal and ototoxically deafened rabbit models by using transcranial - transcutaneous EMI and percutaneous implantable EMI contact with otic capsule. We have also investigated the activity of an implantable lateral cochlear wall EMI at the middle and basal turns in animal model, and found successful activation of the auditory nerve at threshold of 60 T/s (peak) for 1.27 kHz sinusoidal magnetic field. Stimulus trials were used to define the dynamic and operating ranges of the lateral wall implant. No adventitial stimulation of the facial nerve was noted within the dynamic range of the axial shielded implantable EMI. Threshold and saturation EM fields, as well as EM energy needed to activate the facial nerve were also recorded. The magnetically induced middle latency responses (MLRs) was compared with the acoustically induced MLRs and electrically induced MLRs, and the curves of the magnetically induced MLRs were identical with the acoustically induced MLRs.

Maximum responsiveness was observed with magnetic implants of the middle turn of the cochlea, an area that is not reliably approached with intrascalar cochlear implants. The response amplitudes for a given EM stimulus were higher at full fenestration when the implants were in contact with the membranous labyrinth. Degeneration was only identified in the cochlea that was stimulated with EM field in high intensity, larger pulsewidth and high frequency, but short pulsewidth EM stimulus prevented stimulus prevented stimulus induced neural damage.