Cortical activity evoked by a multichannel cochlear prosthesis.

We have recorded electric potentials and neuromagnetic fields evoked by electric stimulation of the auditory nerve in a totally deaf patient with an implanted multichannel prosthesis. The evoked electric responses were a vertex-negative deflection at about 70 ms after stimulus onset and a vertex-positive deflection at about 180 ms. Evoked magnetic responses coinciding with the vertex potential were found in the right hemisphere, ipsilateral to the stimulated ear. The equivalent source of these responses corresponds to activation of the right auditory cortex. In the left hemisphere, the magnetic responses were considerably smaller and less reliable. These results suggest an abnormality of the central auditory pathways in this patient. In the future, neuromagnetic recordings might be used preoperatively to forecast the effectiveness of the possible implantation.