Comparative psychophysical evaluation in cochlear implantation: electrical and magnetic stimulation

Transtympanic electrical stimulation, either in the form of round window or promontory placement of electrode prior to cochlear implantation is an accepted and commonly used psychophysical tool. Certain response parameters have been identified as predictors of outcome. This study compared the subjective auditory responses generated by promontory electrical stimulation (PES) with those from two noninvasive modalities, namely peritympanic electrical stimulation (PTES) and transcranial magnetic stimulation (TMS). Ten postlingually deafened adult cochlear implant candidates were studied. Standard psychophysical parameters were obtained from patients undergoing PES and PTES. A more subjective form of evaluation was conducted for TMS. Subsequently, nine patients received the multichannel Nucleus (Cochlear Corp., Denver, CO, U.S.A.) implant and one patient a Clarion (Advanced Bionics, Sylmar, CA, U.S.A.) implant. Compared with PES. PTES elicited increased threshold responses with similar dynamic ranges between 50 and 400 Hz of stimulation. The differences were, by and large, insignificant. PTES appeared to be a useful alternative in selected individuals owing to its noninvasiveness. TMS, on the other hand, was incapable of clearly inducing auditory percepts. It also produced concomitant facial and trigeminal stimulation, limiting its potential use as a prognostic tool.