A method for the direct electrical stimulation of the auditory system in deaf subjects: a functional magnetic resonance imaging study

Abstract

Purpose: To develop a safe functional magnetic resonance imaging (fMRI) procedure for auditory assessment of deaf subjects.

Materials and methods: A gold-plated tungsten electrode has been developed which has zero magnetic susceptibility. Used with carbon leads and a carbon reference pad, it enables safe, distortion-free fMRI studies of deaf subjects following direct electrical stimulation of the acoustic nerve. Minor pickup of the radio frequency (RF) pulses by the electrode assembly is difficult to eliminate, and a SPARSE acquisition sequence is used to avoid any effects of unintentional auditory nerve stimulation.

Results: The procedure is demonstrated in a deaf volunteer. Activation is observed in the contralateral but not the ipsilateral primary auditory cortex. This is in sharp contrast to studies of auditory processing in hearing subjects, but consistent with the small number of previous positron emission tomography (PET) and MR studies on adult deaf subjects.

Conclusion: The fMRI procedure is able to demonstrate whether the auditory pathway is fully intact, and may provide a useful method for preoperative assessment of candidates for cochlear implantation.